The Danish National Birth Cohort--its background, structure and aim

Combined associations of prepregnancy body mass index and gestational weight gain with the outcome of pregnancy

BACKGROUND

Although both maternal prepregnancy body mass index (BMI) and gestational weight gain (GWG) may affect birth weight, their separate and joint associations with complications of pregnancy and delivery and with postpartum weight retention are unclear.

OBJECTIVES

We aimed to investigate the combined associations of prepregnancy BMI and GWG with pregnancy outcomes and to evaluate the trade-offs between mother and infant for different weight gains.

DESIGN

Data for 60892 term pregnancies in the Danish National Birth Cohort were linked to birth and hospital discharge registers. Self-reported total GWG was categorized as low (<10 kg), medium (10-15 kg), high (16-19 kg), or very high (>or=20 kg). Adjusted associations of prepregnancy BMI and GWG with outcomes of interest were estimated by logistic regression analyses.

RESULTS

High and very high GWG added to the associations of high prepregnancy BMI with cesarean delivery and were strongly associated with high postpartum weight retention. Moreover, greater weight gains and high maternal BMI decreased the risk of growth restriction and increased the risk of the infant's being born large-for-gestational-age or with a low Apgar score. Generally, low GWG was advantageous for the mother, but it increased the risk of having a small baby, particularly for underweight women.

CONCLUSIONS

Heavier women may benefit from avoiding high and very high GWG, which brings only a slight increase in the risk of growth restriction for the infant. High weight gain in underweight women does not appear to have deleterious consequences for them or their infants, but they may want to avoid low GWG to prevent having a small baby.

Prenatal exposure to maternal infections and epilepsy in childhood: a population-based cohort study

OBJECTIVE

We estimated the association between prenatal exposure to maternal infections and the subsequent risk for epilepsy in childhood.

METHODS

We included 90,619 singletons who were born between September 1997 and June 2003 in the Danish National Birth Cohort and followed them up to December 2005. Information on maternal infections during pregnancy (cystitis, pyelonephritis, diarrhea, coughs lasting >1 week, vaginal yeast infection, genital herpes, venereal warts, and herpes labialis) was prospectively reported by mothers in 2 computer-assisted telephone interviews in early and midgestation; information on maternal cystitis and pyelonephritis during late period of pregnancy was also collected in a third interview after birth. Children who received a diagnosis of epilepsy as inpatients or outpatients were retrieved from the Danish National Hospital Register. We identified 646 children with a diagnosis of epilepsy during up to 8 years of follow-up time. Cox proportional hazards regression models were used to estimate incidence rate ratio and 95% confidence interval.

RESULTS

Children who were exposed to maternal cystitis, pyelonephritis, diarrhea, coughs, and/or vaginal yeast infection some maternal infections in prenatal life had an increased risk for epilepsy. Coughs lasting >1 week were associated with an increased risk for epilepsy only in the first year of life, as was vaginal yeast infection only in children who were born preterm. These associations remained unchanged for children without cerebral palsy, congenital malformation, or a low Apgar score at 5 minutes.

CONCLUSIONS

Prenatal exposure to some maternal infections was associated with an increased risk for epilepsy in childhood.

Binge drinking in pregnancy and risk of fetal death

OBJECTIVE

To examine whether the frequency and timing of binge drinking episodes (intake of five or more drinks on one occasion) during the first 16 weeks of pregnancy increase the risk of fetal death.

METHODS

The study is based upon data from 89,201 women who were enrolled in the Danish National Birth Cohort from 1996 to 2002 and participated in an interview that took place in midpregnancy (n=86,752) or after a fetal loss (n=2,449). In total, 3,714 pregnancies resulted in fetal death. Data were analyzed by means of Cox regression models.

RESULTS

Neither the frequency nor the timing of binge episodes was related to the risk of early (at or before 12 completed weeks) or late (13-21 completed weeks) spontaneous abortion. However, three or more binge episodes showed an adjusted hazard ratio of 1.56 (95% confidence interval 1.01-2.40) for stillbirth (22 or more completed weeks) relative to nonbinge drinkers. Women with an average intake of three or more drinks per week and two or more binge drinking episodes had a hazard ratio of 2.20 (95% confidence interval 1.73-2.80) compared with women with no average intake and no binge drinking.

CONCLUSION

Binge drinking three or more times during pregnancy is associated with an increased risk of stillbirth, but neither frequency nor timing of binge drinking was associated with an increased risk of spontaneous abortion in clinically recognized pregnancies.

Pre-natal exposure to paracetamol and risk of wheezing and asthma in children: a birth cohort study

BACKGROUND

Paracetamol use has been associated with increased prevalence of asthma in children and adults, and one study reported an association between pre-natal exposure to paracetamol and asthma in early childhood.

METHODS

To examine if pre-natal exposure to paracetamol is associated with the risk of asthma or wheezing in early childhood, we selected 66 445 women from the Danish National Birth Cohort for whom we had information on paracetamol use during pregnancy and who participated in an interview when their children were 18-months-old and 12 733 women whose children had reached the age of 7 and estimated the prevalence of physician-diagnosed asthma and wheezing at the ages of 18 months and 7 years. We also linked our population to the Danish National Hospital Registry to record all hospitalizations due to asthma up to age of 18 months.

RESULTS

Paracetamol use during any time of pregnancy was associated with a small but statistically significant increased risk of physician-diagnosed asthma or bronchitis among children at 18 months [relative risk (RR) = 1.17, 1.13-1.23)], hospitalizations due to asthma up to 18 months (hazard ratio = 1.24, 1.11-1.38) and physician-diagnosed asthma at 7 years (RR = 1.15, 1.02-1.29). The highest risks were observed for paracetamol use during the first trimester of pregnancy and persistent wheezing (wheezing at both 18 months and 7 years) (RR = 1.45, 1.13-1.85).

CONCLUSION

Paracetamol use during pregnancy was associated with an increased risk of asthma and wheezing in childhood. If this association is causal, we may need to revisit the clinical practice on use of paracetamol during pregnancy.

Physical exercise during pregnancy and the risk of preterm birth: a study within the Danish National Birth Cohort

According to many national recommendations, women should be physically active during pregnancy, but empirical evidence to support this recommendation is sparse. The authors' aim in this study was to examine the relation between physical exercise during pregnancy and the risk of preterm birth. Self-reported data on physical exercise during pregnancy were collected prospectively for 87,232 singleton pregnancies included in the Danish National Birth Cohort between 1996 and 2002. Hazard ratios for preterm birth according to hours of exercise per week, type of exercise, and metabolic equivalent-hours per week, respectively, were calculated using Cox regression analysis. Results showed a reduced risk of preterm birth among the almost 40% of women who engaged in some kind of exercise during pregnancy in comparison with nonexercisers (hazard ratio = 0.82, 95% confidence interval: 0.76, 0.88), but no dose-response relation was seen. The association was not affected by the type of exercise, and the results were not altered when the degree of preterm birth was taken into account. These findings do not indicate any adverse effects of exercise on the risk of preterm birth and therefore do not contradict current recommendations.

Methodological challenges when monitoring the diet of pregnant women in a large study: experiences from the Norwegian Mother and Child Cohort Study (MoBa)

The aim of this article is to describe the main methodological challenges in the monitoring of dietary intake in the Norwegian Mother and Child Cohort Study (MoBa), a pregnancy cohort aiming to include 100 000 participants. The overall challenge was to record dietary patterns in sufficient detail to support future testing of a broad range of hypotheses, while at the same time limiting the burden on the participants. The main questions to be answered were: which dietary method to choose, when in pregnancy to ask, which time period should the questions cover, which diet questions to include, how to perform a validation study, and how to handle uncertainties in the reporting. Our decisions were as follows: using a semi-quantitative food frequency questionnaire (FFQ) (in use from 1 March 2002), letting the participants answer in mid-pregnancy, and asking the mother what she has eaten since she became pregnant. The questions make it possible to estimate intake of food supplements, antioxidants and environmental contaminants in the future. Misreporting is handled by consistency checks. Reports with a calculated daily energy intake of <4.5 and >20 MJ day(-1) are excluded, about 1% in each end of the scale. A validation study confirmed that the included intakes are realistic. The outcome of our methodological choices indicates that our FFQ strikes a reasonable balance between conflicting methodological and scientific interests, and that our approach therefore may be of use to others planning to monitor diet in pregnancy cohorts.

Belated concerns and latent effects: the example of schizophrenia

In this issue of Epidemiology, Stalberg and colleagues report the lack of an association between prenatal ultrasound and risk of schizophrenia in adulthood. These findings contribute to the search for unintended effects of an intervention designed to improve prenatal care. Although no adverse effect of ultrasound was reported, other gestational exposures have been associated with increased risk of schizophrenia. By extending the causal time frame to include long-term latent effects we are confronted with a potential paradox: interventions beneficial in early life may have undetected adverse consequences in adulthood.

Acetaminophen use during pregnancy: effects on risk for congenital abnormalities

OBJECTIVE

We evaluated if acetaminophen, one of the most frequently used drugs among pregnant women is associated with an increased prevalence of congenital abnormalities.

STUDY DESIGN

We selected 88,142 pregnant women and their liveborn singletons from the Danish National Birth Cohort who had information on acetaminophen use during the first trimester of pregnancy. We used the National Hospital Registry to identify 3784 (4.3%) children from the cohort diagnosed with 5847 congenital abnormalities.

RESULTS

Children exposed to acetaminophen during the first trimester of pregnancy (n = 26,424) did not have an increased prevalence of congenital abnormalities (hazard ratio = 1.01, 0.93-1.08) compared with nonexposed children (n = 61,718). No association was found between congenital abnormalities and duration of use during the first trimester. Increased prevalence was not observed for specific abnormalities, except for "medial cysts, fistula, sinus" (congenital abnormalities of the ear, face, and neck, ICD-10 code Q18.8, n = 43) with an adjusted hazard ratio of 2.15 (1.17-3.95).

CONCLUSION

Acetaminophen is not associated with an increased prevalence of congenital abnormalities overall or with any specific group of major abnormalities.

Examination of US puberty-timing data from 1940 to 1994 for secular trends: panel findings

Whether children, especially girls, are entering and progressing through puberty earlier today than in the mid-1900s has been debated. Secular trend analysis, based on available data, is limited by data comparability among studies in different populations, in different periods of time, and using different methods. As a result, conclusions from data comparisons have not been consistent. An expert panel was asked to evaluate the weight of evidence for whether the data, collected from 1940 to 1994, are sufficient to suggest or establish a secular trend in the timing of puberty markers in US boys or girls. A majority of the panelists agreed that data are sufficient to suggest a trend toward an earlier breast development onset and menarche in girls but not for other female pubertal markers. A minority of panelists concluded that the current data on girls' puberty timing for any marker are insufficient. Almost all panelists concluded, on the basis of few studies and reliability issues of some male puberty markers, that current data for boys are insufficient to evaluate secular trends in male pubertal development. The panel agreed that altered puberty timing should be considered an adverse effect, although the magnitude of change considered adverse was not assessed. The panel recommended (1) additional analyses of existing puberty-timing data to examine secular trends and trends in the temporal sequence of pubertal events; (2) the development of biomarkers for pubertal timing and methods to discriminate fat versus breast tissue, and (3) establishment of cohorts to examine pubertal markers longitudinally within the same individuals.

The Generation R Study Biobank: a resource for epidemiological studies in children and their parents

The Generation R Study is a population-based prospective cohort study from fetal life until young adulthood. The study is designed to identify early environmental and genetic causes of normal and abnormal growth, development and health from fetal life until young adulthood. In total, 9,778 mothers were enrolled in the study. Prenatal and postnatal data collection is conducted by physical examinations, questionnaires, interviews, ultrasound examinations and biological samples. Major efforts have been conducted for collecting biological specimens including DNA, blood for phenotypes and urine samples. In this paper, the collection, processing and storage of these biological specimens are described. Together with detailed phenotype measurements, these biological specimens form a unique resource for epidemiological studies focused on environmental exposures, genetic determinants and their interactions in relation to growth, health and development from fetal life onwards.

Infertility, infertility treatment, and fetal growth restriction

OBJECTIVE

To examine the association between infertility, with or without treatment, and fetal growth, as well as perinatal and infant mortality.

METHODS

From the Danish National Birth Cohort (1997-2003), we identified 51,041 singletons born of fertile couples (time to pregnancy 12 months or less), 5,787 born of infertile couples conceiving naturally (time to pregnancy more than 12 months), and 4,317 born after treatment. We defined small for gestational age (SGA) as the lowest 5% of birth weight by sex and gestational age.

RESULTS

Crude estimates suggested an increased risk of perinatal mortality and SGA among infertile couples (treated and untreated), but the odds ratios (ORs) of perinatal mortality among infertile couples were attenuated after adjustment for maternal age and body mass index (1.32, 95% confidence interval [CI] 0.95-1.84 among untreated and 1.26, 95% CI 0.86-1.85 among treated couples). The elevated risk of SGA among infertile couples persisted after adjustment for maternal age, parity, and smoking (OR 1.24, 95% CI 1.10-1.40 among untreated, and OR 1.40, 95% CI 1.23-1.60 among treated). The risk of SGA increased with time to pregnancy, and a longer time to pregnancy was associated with a small reduction in birth weight across the whole distribution.

CONCLUSION

The increased risk of SGA observed among infertile couples with or without infertility treatment suggests that infertility may be a risk factor for intrauterine growth restriction. Treatment per se may have little effect on fetal growth. A small-to-moderate increased risk of perinatal mortality in infertile couples cannot be ruled out due to the small number of cases.

LEVEL OF EVIDENCE

II.

Perfluorinated chemicals and fetal growth: a study within the Danish National Birth Cohort

BACKGROUND

Perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) are man-made, persistent organic pollutants widely spread throughout the environment and human populations. They have been found to interfere with fetal growth in some animal models, but whether a similar effect is seen in humans is uncertain.

OBJECTIVES

We investigated the association between plasma levels of PFOS and PFOA in pregnant women and their infants' birth weight and length of gestation.

METHODS

We randomly selected 1,400 women and their infants from the Danish National Birth Cohort among those who completed all four computer-assisted telephone interviews, provided the first blood samples between gestational weeks 4 and 14, and who gave birth to a single live-born child without congenital malformation. PFOS and PFOA were measured by high performance liquid chromatography-tandem mass spectrometer.

RESULTS

PFOS and PFOA levels in maternal plasma were on average 35.3 and 5.6 ng/mL, respectively. Only PFOA levels were inversely associated with birth weight (adjusted beta = -10.63 g; 95% confidence interval, -20.79 to -0.47 g). Neither maternal PFOS nor PFOA levels were consistently associated with the risk for preterm birth or low birth weight. We observed no adverse effects for maternal PFOS or PFOA levels on small for gestational age.

CONCLUSION

Our nationwide cohort data suggest an inverse association between maternal plasma PFOA levels and birth weight. Because of widespread exposure to these chemicals, our findings may be of potential public health concern.

Maternal and fetal variation in genes of cholesterol metabolism is associated with preterm delivery

OBJECTIVE

To examine the contribution of variants in fetal and maternal cholesterol metabolism genes in preterm delivery (PTD).

STUDY DESIGN

A total of 40 single-nucleotide polymorphisms (SNPs) in 16 genes related to cholesterol metabolism were examined for 414 preterm infants (gestational ages 22 to 36 weeks; comprising 305 singletons and 109 twins) and at least 1 parent. Fetal effects were assessed using the transmission disequilibrium test (TDT) for each SNP, followed by a log linear model-based approach to utilize families with missing parental genotypes for those SNPs showing significance under TDT. Genetic variant effects were examined for a role in PTD, gestational age and birth weight. Maternal effects were estimated using a log linear model-based approach.

RESULT

Among singleton gestations, suggestive association (P<0.01 without adjusting for multiple comparisons) was found between birth weight and fetal DHCR7 gene/SNP combinations (rs1630498, P=0.002 and rs2002064, P=0.003). Among all gestations, suggestive associations were found between PTD and fetal HMGCR (rs2303152, P=0.002) and APOA1 (rs 5070, P=0.004). The result for HMGCR was further supported by the log linear model-based test in the single births (P=0.007) and in all births (P=0.006). New associations (APOE and ABCA1) were observed when birth weight was normalized for gestational age suggesting independent effects of variants on birth weight separate from effects on PTD. Testing for maternally mediated genetic effects has identified suggestive association between ABCA1 (rs4149313, P=0.004) and decreased gestational age.

CONCLUSION

Variants in maternal and fetal genes for cholesterol metabolism were associated with PTD and decreased birth weight or gestational age in this study. Genetic markers may serve as one mechanism to identify high-risk mothers and fetuses for targeted nutritional treatment and/or prevention of low birth weight or PTD.

Milk consumption during pregnancy is associated with increased infant size at birth: prospective cohort study

BACKGROUND

Cow milk contains many potentially growth-promoting factors.

OBJECTIVE

The objective was to examine whether milk consumption during pregnancy is associated with greater infant size at birth.

DESIGN

During 1996-2002, the Danish National Birth Cohort collected data on midpregnancy diet through questionnaires and on covariates through telephone interviews and ascertained birth outcomes through registry linkages. Findings were adjusted for mother's parity, age, height, prepregnant BMI, gestational weight gain, smoking status, and total energy intake; father's height; and family's socioeconomic status The analyses included data from 50,117 mother-infant pairs.

RESULTS

Mean (+/-SD) consumption of milk was 3.1 +/- 2.0 glasses/d. Milk consumption was inversely associated with the risk of small-for gestational age (SGA) birth and directly with both large-for-gestational age (LGA) birth and mean birth weight (P for trend < 0.001). In a comparison of women drinking >or=6 glasses/d with those drinking 0 glasses/d, the odds ratio for SGA was 0.51 (95% CI: 0.39, 0.65) and for LGA was 1.59 (1.16, 2.16); the increment in mean birth weight was 108 g (74, 143 g). We also found graded relations (P < 0.001) for abdominal circumference (0.52 cm; 0.35, 0.69 cm), placental weight (26 g; 15, 38 g), birth length (increment: 0.31 cm; 0.15, 0.46 cm), and head circumference (0.13 cm; 0.04, 0.25 cm). Birth weight was related to intake of protein, but not of fat, derived from milk.

CONCLUSION

Milk intake in pregnancy was associated with higher birth weight for gestational age, lower risk of SGA, and higher risk of LGA.

Leisure time physical exercise during pregnancy and the risk of miscarriage: a study within the Danish National Birth Cohort

OBJECTIVE

To examine the association between leisure time physical exercise during pregnancy and the risk of miscarriage.

DESIGN

Prospective study with elements of retrospective data collection.

SETTING

Denmark 1996-2002.

POPULATION

A total of 92,671 pregnant women enrolled in the Danish National Birth Cohort and interviewed subsequently.

METHODS

Data on exercise during pregnancy and potential confounders were obtained through computer-assisted telephone interviews either during pregnancy or after an early miscarriage. Outcome of pregnancy was identified by register linkage. Using Cox regression analysis, we estimated the hazard ratio (HR) of miscarriage according to weekly amount of exercise and the type of exercise. The HR was estimated for <11, 11-14, 15-18, and 19-22 weeks of gestation, respectively.

MAIN OUTCOME MEASURES

Miscarriage, defined as fetal loss before 22 completed weeks of gestation.

RESULTS

A stepwise increasing relation was found between amount of exercise and risk of miscarriage, where risk of miscarriage increased by amount of exercise up to HR = 3.7 (95% CI 2.9-4.7) for women who exercised more than 7 hours per week compared with nonexercisers. Particularly 'high-impact exercise' was associated with an increased risk of miscarriage. No association was seen between exercise and risk of miscarriage after 18 weeks of gestation.

CONCLUSIONS

This study suggests that exercise early in pregnancy is associated with an increased risk of miscarriage. The results should, however, be interpreted cautiously as potential bias arising from retrospective data collection may explain part of the association.

Examining life-course influences on chronic disease: the importance of birth cohort studies from low- and middle- income countries. An overview

The objectives of this overview are to describe the past and potential contributions of birth cohorts to understanding chronic disease aetiology; advance a justification for the maintenance of birth cohorts from low- and middle-income countries (LMIC); provide an audit of birth cohorts from LMIC; and, finally, offer possible future directions for this sphere of research. While the contribution of birth cohorts from affluent societies to understanding disease aetiology has been considerable, we describe several reasons to anticipate why the results from such studies might not be directly applied to LMIC. More than any other developing country, Brazil has a tradition of establishing, maintaining and exploiting birth cohort studies. The clear need for a broader geographical representation may be precipitated by a greater collaboration worldwide in the sharing of ideas, fieldwork experience, and cross-country cohort data comparisons in order to carry out the best science in the most efficient manner. This requires the involvement of a central overseeing body--such as the World Health Organization--that has the respect of all countries and the capacity to develop strategic plans for 'global' life-course epidemiology while addressing such issues as data-sharing. For rapid progress to be made, however, there must be minimal bureaucratic entanglements.

Medical abortion and the risk of subsequent adverse pregnancy outcomes

BACKGROUND

The long-term safety of surgical abortion in the first trimester is well established. Despite the increasing use of medical abortion (abortion by means of medication), limited information is available regarding the effects of this procedure on subsequent pregnancies.

METHODS

We identified all women living in Denmark who had undergone an abortion for nonmedical reasons between 1999 and 2004 and obtained information regarding subsequent pregnancies from national registries. Risks of ectopic pregnancy, spontaneous abortion, preterm birth (at <37 weeks of gestation), and low birth weight (<2500 g) in the first subsequent pregnancy in women who had had a first-trimester medical abortion were compared with risks in women who had had a first-trimester surgical abortion.

RESULTS

Among 11,814 pregnancies in women who had had a previous first-trimester medical abortion (2710 women) or surgical abortion (9104 women), there were 274 ectopic pregnancies (respective incidence rates, 2.4% and 2.3%), 1426 spontaneous abortions (12.2% and 12.7%), 552 preterm births (5.4% and 6.7%), and 478 births with low birth weight (4.0% and 5.1%). After adjustment for maternal age, interval between pregnancies, gestational age at abortion, parity, cohabitation status, and urban or nonurban residence, medical abortion was not associated with a significantly increased risk of ectopic pregnancy (relative risk, 1.04; 95% confidence interval [CI], 0.76 to 1.41), spontaneous abortion (relative risk, 0.87; 95% CI, 0.72 to 1.05), preterm birth (relative risk, 0.88; 95% CI, 0.66 to 1.18), or low birth weight (relative risk, 0.82; 95% CI, 0.61 to 1.11). Gestational age at medical abortion was not significantly associated with any of these adverse outcomes.

CONCLUSIONS

We found no evidence that a previous medical abortion, as compared with a previous surgical abortion, increases the risk of spontaneous abortion, ectopic pregnancy, preterm birth, or low birth weight.

Maternal plasma cytokines in early- and mid-gestation of normal human pregnancy and their association with maternal factors

Few studies have assessed longitudinal changes in circulating cytokine levels during normal pregnancy. We have examined the natural history of maternal plasma cytokines from early- to mid-pregnancy in a large, longitudinal cohort. Multiplex flow cytometry was used to measure interleukin (IL)-2, IL-6, IL-12, tumor necrosis factor (TNF)-alpha, interferon (IFN)-gamma and granulocyte-macrophage colony-stimulating factor (GM-CSF) in early- (median [IQR]: 8.5 weeks [7.1, 10.0]) and mid-pregnancy (25.0 [24.1, 26.1]) from 1274 Danish women delivering singleton term infants. GM-CSF decreased from early- to mid-pregnancy (median percent change [95% CI]: -51.3% [-59.1%, -41.8%]), while increases were observed in IL-6 (24.3% [4.6%, 43.9%]), IL-12 (21.3% [8.9%, 35.7%]) and IFN-gamma (131.7% [100.2%, 171.6%]); IL-2 (-2.8% [-11.5%, 0.0%]) and TNF-alpha (0% [-5.9%, 25.6%]) remained stable. Positive correlations were found between all cytokines, both in early- and mid-pregnancy (all p<0.001). Early- and mid-pregnancy levels were rank-correlated for IL-2, IL-12, TNF-alpha and GM-CSF, but not IL-6 and IFN-gamma; these correlations were generally weaker than correlations between different cytokines at a single time point in pregnancy. Women with a pre-pregnancy BMI <18.5 had reduced levels of IFN-gamma and GM-CSF compared to women in other BMI categories, while women aged >or=35 years had elevated IL-2, IL-6, TNF-alpha and IFN-gamma. Early-pregnancy levels of TNF-alpha were higher in women with a prior preterm delivery. Cytokine levels were not associated with gravidity. In conclusion, cytokines were detected in plasma during early- and mid-pregnancy, with IL-6, IL-12, IFN-gamma and GM-CSF concentrations varying over pregnancy. Concentrations may depend on BMI, maternal age and prior preterm delivery.

Storage policies and use of the Danish Newborn Screening Biobank

After routine newborn screening, residual dried blood spot samples (DBSS) are stored at -20 degrees C in the Danish Newborn Screening Biobank (NBS-Biobank), which contains DBSS from virtually all newborns in Denmark since 1982--about 1.8 million samples. The purpose of the storage is: (1) diagnosis and treatment of congenital disorders including documentation, repeat testing, quality assurance, statistics and improvement of screening methods; (2) diagnostic use later in infancy after informed consent; (3) legal use after court order; (4) the possibility of research projects after approval by the Scientific Ethical Committee System in Denmark, The Danish Data Protection Agency and the NBS-Biobank Steering Committee. The operation and use of the NBS-Biobank has until recently been regulated by an executive order of 1993 from the Danish Ministry of Health. The Ethical Council, the Central Scientific Ethical Committee and the National Board of Health were also involved in the regulations. These regulations have now been replaced by detailed general operational guidelines for biobanks in Denmark according to Acts on Processing of Personal Data, Patient's Rights, Health 546/2005 and the Biomedical Research Ethics Committee System. No specific Act on biobanks per se has been made in Denmark, but the new regulations and guidelines make the operations of the Danish NBS-Biobank even more clear-cut and safe. The Danish NBS-Biobank has been used in several research projects for aetiological studies of a number of disorders, recently employing new sensitive multiplex technologies and genetic analyses utilizing whole-genome amplified DNA.

High prepregnant body mass index is associated with early termination of full and any breastfeeding in Danish women

BACKGROUND

An association between high prepregnant body mass index (BMI) and early termination of breastfeeding has been observed, but this finding may have depended on the sociocultural context.

OBJECTIVE

The objective was to determine whether this association was stronger with increasing maternal obesity, was modified by gestational weight gain, and still existed when there was greater social support for breastfeeding.

DESIGN

Study participants (37 459 women) were drawn from the Danish National Birth Cohort. The association of prepregnant BMI and gestational weight gain with the termination of full or any breastfeeding by 1, 16, or 20 wk postpartum was assessed with logistic regression analyses, and the risk of early termination of full and any breastfeeding during the first 18 mo postpartum was assessed with Poisson regression analyses.

RESULTS

The risk of early termination of any (with similar results for full) breastfeeding rose progressively with increasing prepregnant BMI values (in kg/m(2)), from 1.12 (95% CI: 1.09, 1.16) for overweight (BMI = 25.0-29.9) women to 1.39 (95% CI: 1.19, 1.63) for obese class III women (BMI >or= 40) compared with normal-BMI women. Gestational weight gain did not add to or modify the association between prepregnant BMI and breastfeeding.

CONCLUSIONS

These findings extend the observation to a broader range of BMIs that the greater the prepregnant BMI, the earlier the termination of breastfeeding. Together with the fact that this association was evident in a more supportive social context for breastfeeding, these findings suggest a biological basis for the association.

Population-based investigations to study the association of cardiovascular polymorphisms and adverse pregnancy outcome

Adverse pregnancy outcome refers to placenta-mediated complications that may share a common etiopathogenesis in some cases. Unraveling associations between prothrombotic genetic predispositions and these pregnancy disorders, namely recurrent fetal loss, stillbirth, severe preeclampsia, intrauterine growth restriction, and placental abruption, requires rigorous epidemiological studies involving large cohorts of patients with sufficient numbers of the adverse pregnancy outcomes in question. Such is the case with the Denmark National Birth Cohort, which was initiated in 1996 and followed pregnant women giving birth from the years 1996 to 2002. In addition, national registers exist which can be linked together. Two studies have been initiated. One is a retrospective cohort study concerning primiparous women, with singleton pregnancy and with no identifiable congenital malformation. The purpose of this study is to determine the long-term cardiovascular risk of women whose pregnancies were complicated by adverse pregnancy outcome. Preliminary evidence suggests that the presence of an adverse pregnancy outcome augments the cardiovascular disease risk by an odds ratio of 1.21 (P < 0.001). The second study focuses on pro-thrombotic and cardiovascular genetic polymorphisms in a nested-case control study comparing pregnancies with and without an adverse pregnancy outcome in the index pregnancy. This study will be adequately powered to determine the relationship between adverse pregnancy outcome and pro-thrombotic and cardiovascular genetic polymorphisms. These studies are urgently needed to accurately assess the linkage between family history, presence of adverse pregnancy outcome, and long-term cardiovascular risk.

Validity of preeclampsia-related diagnoses recorded in a national hospital registry and in a postpartum interview of the women

In a population-based sample, the authors examined the validity of preeclampsia and related diagnoses recorded in a mandatory Danish national hospital discharge registry and in a standardized telephone interview of women who gave birth between 1998 and 2002. Using a "gold standard" for preeclampsia defined in accordance with the guidelines from the American College of Obstetricians and Gynecologists, the authors reviewed hospital charts of 3,039 women and found that 61 of 88 preeclampsia cases (69.3%) and 24 of 55 cases of serious subtypes of preeclampsia (43.6%) were recorded as such by the registry. A total of 21 of 2,951 women without preeclampsia (0.71%) had a preeclampsia diagnosis in the registry. All registrations of serious subtypes of preeclampsia reflected true cases. The positive predictive value of a preeclampsia diagnosis in the registry was 74.4%. Including interview data reduced the sample size to 2,307 women. In this sample, of 62 women with preeclampsia, 45 (72.6%) reported in the interview to have had preeclampsia. Of 2,245 women with no preeclampsia, 31 (1.4%) reported to have had preeclampsia. The positive predictive value of the women's own report on preeclampsia was 59.2%. The authors conclude, for the purpose of etiologic studies, that the registry had acceptable validity, whereas the usefulness of self-reported information may be limited.

Relative validity of a food frequency questionnaire used in the Inter99 study

OBJECTIVE

To evaluate the validity of the Inter99 food frequency questionnaire (FFQ) compared with a 28-days' diet history and biomarkers.

SUBJECTS

A random sample of 13 016 individuals were drawn from a general population and invited for a health screening programme. Participation rate was 52.5%. All high-risk individuals were re-invited for assessment after 1 and 3 years and completed a 198-item FFQ at all three occasions. Participants attending for 3 years follow-up were invited to participate in the validation study, including a 28-days' diet history, a 24-h urine collection and a fasting blood sample. Overall, 264 subjects participated.

RESULTS

Spearman's rank correlation coefficients between the two dietary methods ranged from 0.31(beta-carotene) to 0.64 (fruits) in men and from 0.31 (polyunsaturated fat and sodium) to 0.64 (fruits) for women. The proportion of individuals classified in the same or adjacent quintiles were, on average, 72% for men and 69% for women. Gross misclassification was found on average in 2%. The correlation coefficients of the residuals ranged from 0.27 (sodium) to 0.61 (fruits) for men and from 0.21 (sodium) to 0.62 (B12-vitamin) for women. Correlation coefficients between fruit and vegetable intake and carotenoids ranged from -0.08 (lycopene) to 0.44 (alpha-carotene). For the residuals the correlation coefficients ranged from -0.004 (lycopene) to 0.47 (alpha-carotene).

CONCLUSION

The Inter99 FFQ and the residuals of the intake provide acceptable classification of individuals according to their dietary intakes and the FFQ gives a good quantitative measurement of key dietary components.

Infertility, infertility treatment and twinning: the Danish National Birth Cohort

BACKGROUND

We have previously observed that an increasing time to pregnancy (TTP) is associated with a reduced frequency of twin deliveries in couples not receiving infertility treatment. By using updated information, we assessed the frequencies of dizygotic (DZ) and monozygotic (MZ) twin deliveries as a function of infertility (TTP > 12 months), as well as infertility treatment.

METHODS

From the Danish National Birth Cohort (1997-2003), we identified 51 730 fertile couples with TTP 12 months and 5163 infertile couples who conceived after treatment. Information on zygosity, available for part of the cohort (1997-2000), was based on standardized questions on the similarities between the twins at the age of 3-5 years.

RESULTS

Compared with fertile couples, the frequency of DZ twin deliveries was lower for infertile couples conceiving naturally (odds ratio 0.4, 95% confidence interval 0.2-0.7) and was much higher for infertile couples conceiving after treatment (17.3, 14.4-20.7). The frequency of DZ twin deliveries decreased with TTP in untreated couples, whereas the frequency of MZ twin deliveries remained constant.

CONCLUSIONS

The frequency of DZ twin deliveries decreased with TTP and substantially increased with infertility treatment, whereas MZ twin deliveries remained substantially unchanged.

Major dietary patterns in pregnancy and fetal growth

OBJECTIVES

To investigate possible associations between maternal diet during pregnancy and fetal growth.

METHOD

Factor analysis was used to explore dietary patterns among pregnant women. The association between maternal dietary patterns and fetal growth (in terms of small for gestational age, SGA) was investigated by logistic regression. Prospective cohort study, including information on 44 612 women in Denmark.

RESULTS

Two major dietary patterns were defined: the first pattern was characterized by red and processed meat, high-fat dairy, and the second pattern was characterized by intake of vegetables, fruits, poultry and fish. Women were classified into three classes according to their diet: the first class had high intake of foods of the first dietary pattern, and was classified as 'the Western diet', the second class preferred foods of the second pattern and was classified as the 'Health Conscious'; and the third one had eaten foods of both patterns, and was classified as the 'Intermediate'. The odds ratio of having a small for gestational-age infant (with a birth weight below the 2.5th percentile for gestational age and gender) was 0.74 (95% CI 0.64-0.86) for women in the Health Conscious class compared with women in the Western Diet class. The analyses were adjusted for parity, maternal smoking, age, height, pre-pregnancy weight and father's height.

CONCLUSIONS

Our results indicated that a diet in pregnancy, based on red and processed meat and high-fat diary, was associated with increased risk for SGA. Further studies are warranted to identify specific macro-, or micronutrients that may be underlying these associations.

Subfecundity in overweight and obese couples

BACKGROUND

Recent studies indicate that not only women's but also men's obesity has adverse effects on fecundity and since fecundity is a couple concept, we examined fecundity in relation to overweight and obesity of the couple. We also examined the association between weight changes and fecundity over time.

METHODS

Between 1996 and 2002, 64 167 pregnant women enrolled in the Danish National Birth Cohort were interviewed during and 18 months after pregnancy. Information on body mass index (BMI) and waiting time to pregnancy (TTP) was available for 47 835 couples.

RESULTS

Among men and women with a BMI of 18.5 kg/m(2) or more, we found a dose-response relationship between increasing BMI group and subfecundity (a TTP of more than 12 months): Odds ratio (OR) = 1.32 (95% CI: 1.26-1.37) for women and OR = 1.19 (95% CI: 1.14-1.24) for men. Among 2374 women with an initial BMI of 18.5 kg/m(2) or more, who participated more than once in the Danish National Birth Cohort, each kilogram increment in weight between the two pregnancies was associated with a 2.84 (95% CI: 1.33-4.35) days longer TTP.

CONCLUSIONS

Couples have a high risk of being subfecund if they are both obese.

Iron supplement use among Danish pregnant women

OBJECTIVES

To evaluate compliance with the national recommendation on supplemental iron to all pregnant women in Denmark and to explore differences between compliers and non-compliers with respect to dietary habits and other lifestyle factors.

DESIGN

Intake of supplemental iron from pure iron supplements and from multivitamin and mineral preparations was estimated in mid-pregnancy.

SETTING

Nationwide cohort study, the Danish National Birth Cohort (DNBC), comprising more than 100,000 women recruited in early pregnancy.

SUBJECTS

Information on diet and dietary supplements was available for 54,371 women. Of these, information on lifestyle factors was available for 50,902 women.

RESULTS

A high compliance with the recommendation was found, as approximately 77% of the women reported use of iron supplements during pregnancy. However, many of the compliers did not obtain the recommended doses of iron, which can partly be explained by the lack of iron preparations of appropriate doses available on the Danish market. Compliance with the recommendation was associated with age above 20 years, primiparity, body mass index<30 kg m- 2, non-smoking and long education. No major differences were seen in dietary intake between compliers and non-compliers.ConclusionOverall, a high compliance rate was found among participants of the DNBC but a clarification on daily dose is needed, and more concern should be paid to vulnerable groups such as young, smoking women and women with no or short education.

Exposición a contaminantes atmosféricos durante el embarazo y desarrollo prenatal y neonatal: protocolo de investigación en el proyecto INMA (Infancia y Medio Ambiente)

INTRODUCTION

The INMA (INfancia y Medio Ambiente [Spanish for Environment and Childhood]) project is a cooperative research network. This project aims to study the effects of environment and diet on fetal and early childhood development. This article aims to present the air pollutant exposure protocol during pregnancy and fetal and early childhood development of the INMA project.

METHODS

The information to assess air pollutant exposure during pregnancy is based on outdoor measurement of air pollutants (nitrogen dioxide [NO2], volatile organic compounds [VOC], ozone, particulate matter [PM10, PM2,5 ] and of their composition [polycyclic aromatic hydrocarbons]); measurement of indoor and personal exposure (VOC and NO2); urinary measurement of a biological marker of hydrocarbon exposure (1-hydroxypyrene); and data gathered by questionnaires and geographic information systems. These data allow individual air pollutant exposure indexes to be developed, which can then be used to analyze the possible effects of exposure on fetal development and child health.

CONCLUSION

This protocol and the type of study allow an approximation to individual air pollutant exposure to be obtained. Finally, the large number of participants (N = 4,000), as well as their geographic and social diversity, increases the study's potential.

Effect of reducing caffeine intake on birth weight and length of gestation: randomised controlled trial

OBJECTIVE

To estimate the effect of reducing caffeine intake during pregnancy on birth weight and length of gestation.

DESIGN

Randomised double blind controlled trial.

SETTING

Denmark.

PARTICIPANTS

1207 pregnant women drinking at least three cups of coffee a day, recruited before 20 weeks' gestation.

INTERVENTIONS

Caffeinated instant coffee (568 women) or decaffeinated instant coffee (629 women).

MAIN OUTCOME MEASURES

Birth weight and length of gestation.

RESULTS

Data on birth weight were obtained for 1150 liveborn singletons and on length of gestation for 1153 liveborn singletons. No significant differences were found for mean birth weight or mean length of gestation between women in the decaffeinated coffee group (whose mean caffeine intake was 182 mg lower than that of the other group) and women in the caffeinated coffee group. After adjustment for length of gestation, parity, prepregnancy body mass index, and smoking at entry to the study the mean birth weight of babies born to women in the decaffeinated group was 16 g (95% confidence interval -40 to 73) higher than those born to women in the caffeinated group. The adjusted difference (decaffeinated group-caffeinated group) of length of gestation was -1.31 days (-2.87 to 0.25).

CONCLUSION

A moderate reduction in caffeine intake in the second half of pregnancy has no effect on birth weight or length of gestation.

TRIAL REGISTRATION

Clinical Trials NCT00131690 [ClinicalTrials.gov].

Cryptorchidism and maternal alcohol consumption during pregnancy

BACKGROUND

Prenatal exposure to alcohol can adversely affect the fetus. We investigated the association between maternal alcohol consumption during pregnancy and cryptorchidism (undescended testis) among newborn boys.

METHODS

We examined 2,496 boys in a prospective Danish-Finnish birth cohort study for cryptorchidism at birth (cryptorchid/healthy: 128/2,368) and at 3 months of age (33/2,215). Quantitative information on alcohol consumption (average weekly consumption of wine, beer, and spirits and number of binge episodes), smoking, and caffeine intake was obtained by questionnaire and/or interview once during the third trimester of pregnancy, before the outcome of the pregnancy was known. For a subgroup (n = 465), information on alcohol consumption was obtained twice during pregnancy by interviews.

RESULTS

We investigated maternal alcohol consumption both as a continuous variable and categorized. The odds for cryptorchidism increased with increasing weekly alcohol consumption. After adjustment for confounders (country, smoking, caffeine intake, binge episodes, social class, maternal age, parity, maturity, and birth weight) the odds remained significant for women with a weekly consumption of five or more alcoholic drinks (odds ratio = 3.10; 95% confidence interval, 1.05-9.10).

CONCLUSIONS

Regular alcohol intake during pregnancy appears to increase the risk of congenital cryptorchidism in boys. The mechanisms for this association are unknown. Counseling of pregnant women with regard to alcohol consumption should also consider this new finding.

Maternal vaccination and preterm birth: using data mining as a screening tool

OBJECTIVE

The main purpose of this study was to identify possible associations between medicines used in pregnancy and preterm deliveries using data mining as a screening tool.

SETTINGS

Prospective cohort study.

METHODS

We used data mining to identify possible correlates between preterm delivery and medicines used by 92,235 pregnant Danish women who took part in the Danish National Birth Cohort (DNBC). We then evaluated the association between one of the identified exposures (vaccination) and the risk for preterm birth by using logistic regression. The women were classified into groups according to their exposure to vaccination. The regression analyses were adjusted for the following covariates: parity, infant's gender, maternal Body-Mass Index (BMI), age, smoking, drinking, job, number of inhabitants in the place of residence, infections, diabetes, high blood pressure and preeclampsia.

MAIN OUTCOME MEASURE

Preterm birth, a delivery occurring before the 259th day of gestation (i.e., less than 37 full weeks).

RESULTS

Data mining had indicated that maternal vaccination (among other factors) might be related to preterm birth. The following regression analysis showed that, the women who reported being vaccinated shortly before or during gestation had a slightly higher risk of giving preterm birth (O.R. = 1.14; 95% CI 1.04-1.25) as compared to the non-vaccinated group.

CONCLUSION

Whether the association between maternal vaccination and the risk for preterm birth found here is causal or not deserves further studies. Data mining, especially with additional refinements, may be a valuable and very efficient tool to screen large databases for relevant information which can be used in clinical and public health research.

Low compliance with recommendations on folic acid use in relation to pregnancy: is there a need for fortification?

Objective:

As a means to prevent neural tube defects (NTDs), women planning pregnancy in Denmark are recommended to take a dietary supplement of 400 μg folic acid daily during the periconceptional period. We examined compliance with this recommendation in a national survey.

Design:

Cohort study on pregnant women in Denmark.

Setting:

The Danish National Birth Cohort (DNBC).

Subjects:

From November 2000 to February 2002, 22 000 pregnant women were recruited for DNBC. Use of dietary supplements was recorded at enrolment. Compliance with the recommendation was related to an information campaign that took place during the second half of 2001, and to lifestyle factors provided in a telephone interview by the end of the first trimester of pregnancy.

Results:

An increase was seen in the proportion of women complying with the recommendation in the study period and this coincided with the information campaign events. However, even at the end of the period, only 22.3% of the women who had planned their pregnancy fully complied with the recommendation. No increase at all was seen in periconceptional folic acid use among women with unplanned pregnancies. Young age, low education and smoking were identified as factors that determined non-compliance.

Conclusions:

Alternative and more effective strategies are needed if the Danish population is to benefit fully from the knowledge that folic acid prevents NTDs. Future strategies should not only target vulnerable groups, such as the less educated and the young, but also women who get pregnant without planning this. The only possible way to reach the last group may be through fortification of foods with folic acid.

Validity of protein, retinol, folic acid and n–3 fatty acid intakes estimated from the food-frequency questionnaire used in the Danish National Birth Cohort

Objective

To validate intakes of protein, folic acid, retinol and n–3 fatty acids estimated from a food-frequency questionnaire in week 25 of pregnancy (FFQ-25).

Design

Validation was done against a 7-day weighed food diary (FD) and biomarkers of the nutrients in gestation week 32–38.

Subjects and setting

The FFQ-25 to be validated was used in the Danish National Birth Cohort comprising 101 042 pregnant Danish women, of whom 88 participated in the present validation study.

Results

Estimated intakes of protein, retinol and folic acid did not differ significantly between the two dietary methods, but intake of n–3 fatty acids was one third larger when estimated from the FFQ-25. The intakes estimated from the two dietary methods were all significantly correlated, ranging from 0.20 for retinol intake to 0.57 for folic acid intake. Sensitivities of being correctly classified into low and high quintiles were between 0.22 and 0.77, and specificities were between 0.62 and 0.89. Urinary protein content did not correlate significantly with protein estimated from the FFQ (r = 0.17, P > 0.05), but did with intake estimated from the FD (r = 0.56, P < 0.0001). Erythrocyte folate correlated significantly with the estimated total intake from the FFQ (r = 0.55, P < 0.0001) and the FD (r = 0.52, P < 0.0001). No correlations with plasma retinol were found. Erythrocyte eicosapentaenoic acid (C20:5n-3) correlated significantly with n–3 fatty acids intake estimated from both the FFQ-25 (r = 0.37, P < 0.001) and the FD (r = 0.62, P < 0.0001).

Conclusion

The FFQ-25 gives reasonable valid estimates of protein, retinol and folic acid intakes, but seems to overestimate intake of n–3 fatty acids.

Does low participation in cohort studies induce bias?

BACKGROUND

Participation rates in large cohort studies have decreased during the last 2 decades. The consequences of this trend for relative risk estimation are unknown.

METHODS

The impact of a low participation rate (30%) on the Danish National Birth Cohort was examined among 49,751 women from the source population, including 15,373 participants in the cohort study. On the basis of independent data collection, we estimated odds ratios (ORs) in the source population and among participants for 3 exposure-risk associations: (a) in vitro fertilization and preterm birth, (b) smoking during pregnancy and birth of a small-for-gestational-age infant, and (c) prepregnancy body mass index and antepartum stillbirth. The effect of nonparticipation was described by a relative odds ratio (ROR), calculated as the OR(participants)/OR(source population). Two methods for calculation of confidence intervals for the relative odds ratio also were assessed.

RESULTS

The effect of nonparticipation on the selected ORs was small. The relative ORs were close to one and the bias was never larger than 16%, although some of the confidence intervals were wide. The 2 methods for calculation of confidence intervals gave very similar results and a small simulation study showed that the coverage probabilities were close to the 95% nominal level.

CONCLUSION

For the 3 chosen associations, the ORs were not biased by nonparticipation. The results are reassuring for studies based on the Danish cohort and similar cohorts of pregnant women. The methodology used to compute confidence intervals for the relative odds ratios performed well in the scenarios considered.

Prenatal exposure to loratadine in children with hypospadias: a nested case-control study within the Danish National Birth Cohort

The aim of this study was to examine the risk of hypospadias after reported exposure to loratadine and other antihistamines during pregnancy, based on data from the Danish National Birth Cohort. We examined the risk of hypospadias in a nested case-control design based on women enrolled in the Danish National Birth Cohort from 1998 to 2002 ( approximately 95,000 pregnant women). Data on maternal use of medicine in pregnancy were retrieved from questionnaires and telephone interviews, and data on birth outcomes were obtained from the Hospital Discharge Registry (HDR). Within the Danish National Birth Cohort, we identified cases with a diagnosis of hypospadias and randomly selected 10 controls per case without such a diagnosis (matched by date of birth). We identified 203 cases of hypospadias recorded in the HDR within 1 year postpartum and 2030 controls. One case (0.5%) and 25 (1.2%) controls reported exposure to loratadine in the first trimester or up to 30 days before the time of conception. The adjusted odds ratio (OR) for hypospadias among users of loratadine relative to nonusers was 0.9 (95% CI: 0.1-6.9) and the corresponding OR for other antihistamines was 0.5 (95% CI: 0.1-1.9). These data do not indicate an increased risk of hypospadias associated with maternal exposure to loratadine. In addition, this study does not suggest any risk differential between maternal exposure to loratadine and other antihistamines. However, the statistical precision of the risk estimates was low.

Atopic disposition, wheezing, and subsequent respiratory syncytial virus hospitalization in Danish children younger than 18 months: a nested case-control study

OBJECTIVES

This study examined whether atopic disposition, wheezing, and atopic disorders increased the risk of hospitalizations because of respiratory syncytial virus in children between birth and 18 months of age.

PATIENTS AND METHODS

Relative risks for respiratory syncytial virus hospitalization were studied in a nested 1:5 case-control design using exposure information obtained from interviews with mothers of 2564 case and 12,816 control children who had been followed prospectively from birth and until 18 months of age as participants in the Danish National Birth Cohort. Information on the children's ages at respiratory syncytial virus hospitalization, presentation of infrequent wheezing, recurrent wheezing, and atopic dermatitis were used to study these associations chronologically.

RESULTS

The adjusted relative risk of respiratory syncytial virus hospitalization in the offspring was 1.11 for maternal atopic dermatitis, 1.72 for maternal asthma, and 1.23 for paternal asthma. Atopic dermatitis in the child was associated with an increased risk of subsequent respiratory syncytial virus hospitalization among infants <6 months of age. Infrequent wheezing was associated with a relative risk of subsequent respiratory syncytial virus hospitalization of 2.98 and recurrent wheezing with a relative risk of 5.90. These associations were present also if infants with medical risk factors were excluded from the analysis.

CONCLUSIONS

Asthmatic disposition and wheezing were strong determinants of subsequent respiratory syncytial virus hospitalization in Danish children <18 months of age.

The National Children's Study: a 21-year prospective study of 100,000 American children

Prospective, multiyear epidemiologic studies have proven to be highly effective in discovering preventable risk factors for chronic disease. Investigations such as the Framingham Heart Study have produced blueprints for disease prevention and saved millions of lives and billions of dollars. To discover preventable environmental risk factors for disease in children, the US Congress directed the National Institute of Child Health and Human Development, through the Children's Health Act of 2000, to conduct the National Children's Study. The National Children's Study is hypothesis-driven and will seek information on environmental risks and individual susceptibility factors for asthma, birth defects, dyslexia, attention-deficit/hyperactivity disorder, autism, schizophrenia, and obesity, as well as for adverse birth outcomes. It will be conducted in a nationally representative, prospective cohort of 100,000 US-born children. Children will be followed from conception to 21 years of age. Environmental exposures (chemical, physical, biological, and psychosocial) will be assessed repeatedly during pregnancy and throughout childhood in children's homes, schools, and communities. Chemical assays will be performed by the Centers for Disease Control and Prevention, and banks of biological and environmental samples will be established for future analyses. Genetic material will be collected on each mother and child and banked to permit study of gene-environment interactions. Recruitment is scheduled to begin in 2007 at 7 Vanguard Sites and will extend to 105 sites across the United States. The National Children's Study will generate multiple satellite studies that explore methodologic issues, etiologic questions, and potential interventions. It will provide training for the next generation of researchers and practitioners in environmental pediatrics and will link to planned and ongoing prospective birth cohort studies in other nations. Data from the National Children's Study will guide development of a comprehensive blueprint for disease prevention in children.

Infertility, infertility treatment, and congenital malformations: Danish national birth cohort

OBJECTIVES

To examine whether infertile couples (with a time to pregnancy of > 12 months), who conceive naturally or after treatment, give birth to children with an increased prevalence of congenital malformations.

DESIGN

Longitudinal study.

SETTING

Danish national birth cohort.

PARTICIPANTS

Three groups of liveborn children and their mothers: 50,897 singletons and 1366 twins born of fertile couples (time to pregnancy < or = 12 months), 5764 singletons and 100 twins born of infertile couples who conceived naturally (time to pregnancy > 12 months), and 4588 singletons and 1690 twins born after infertility treatment.

MAIN OUTCOME MEASURES

Prevalence of congenital malformations determined from hospital discharge diagnoses.

RESULTS

Compared with singletons born of fertile couples, singletons born of infertile couples who conceived naturally or after treatment had a higher prevalence of congenital malformations-hazard ratios 1.20 (95% confidence interval 1.07 to 1.35) and 1.39 (1.23 to 1.57). The overall prevalence of congenital malformations increased with increasing time to pregnancy. When the analysis was restricted to singletons born of infertile couples, babies born after treatment had an increased prevalence of genital organ malformations (hazard ratio 2.32, 1.24 to 4.35) compared with babies conceived naturally. No significant differences existed in the overall prevalence of congenital malformations among twins.

CONCLUSIONS

Hormonal treatment for infertility may be related to the occurrence of malformations of genital organs, but our results suggest that the reported increased prevalence of congenital malformations seen in singletons born after assisted reproductive technology is partly due to the underlying infertility or its determinants. The association between untreated infertility and congenital malformations warrants further examination.

The Dietary Quality Score: validation and association with cardiovascular risk factors: the Inter99 study

OBJECTIVE

To develop and assess the validity of the Dietary Quality Score (DQS) and investigate the association with cardiovascular risk factors.

DESIGN

Cross-sectional population-based study.

SETTING

Copenhagen County, Glostrup, Denmark.

SUBJECTS

A random sample of 12,934 men and women aged 30-60 years were invited to a health examination. A total of 6542 participants were included in the statistical analysis.

METHODS

The DQS was developed using eight questions from a 48-item food frequency questionnaire (FFQ) and validated using a 198-item FFQ. Associations between the DQS and fasting serum lipids, homocysteine, blood pressure and the absolute risk of ischaemic heart disease (IHD) were explored.

RESULTS

A higher DQS was shown to be associated with higher dietary quality in general, including a low intake of fat, especially saturated fat; a high intake of fibre; various vitamins and minerals; and fruit, fish, vegetables and whole-grain products. A higher score according to the DQS was significantly negatively associated with total cholesterol (P=0.0031), triglyceride (P=0.0406), low-density lipoprotein-cholesterol (P=0.0071), homocysteine (P<0.0001) and the absolute risk of IHD (P<0.0001), adjusted for sex, age, smoking habits and physical activity level.

CONCLUSIONS

The DQS is a simple, valid and quick tool to make a rough classification of individuals into groups with high, average and low dietary quality. The DQS is negatively associated with serum lipids, homocysteine and the absolute risk of IHD.

SPONSORSHIP

The Inter99 study is supported economically by The Danish Medical Research Council, The Danish Centre for Evaluation and Health Technology Assessment, Novo Nordisk, Copenhagen County, The Danish Heart Foundation, The Danish Pharmaceutical Association, Augustinus Foundation, Ib Henriksen Foundation and Becket Foundation, Copenhagen County.

The Generation R Study: Design and cohort profile

The Generation R Study is a population-based prospective cohort study from fetal life until young adulthood. The study is designed to identify early environmental and genetic causes of normal and abnormal growth, development and health from fetal life until young adulthood. The study focuses on four primary areas of research: (1) growth and physical development; (2) behavioral and cognitive development; (3) diseases in childhood; and (4) health and healthcare for pregnant women and children. In total, 9778 mothers with a delivery date from April 2002 until January 2006 were enrolled in the study. Of all eligible children at birth, 61% participate in the study. Data collection in the prenatal phase included physical examinations, questionnaires, fetal ultrasound examinations and biological samples. In addition, more detailed assessments are conducted in a subgroup of 1232 pregnant women and their children. The children form a prenatally recruited birth-cohort that will be followed until young adulthood. Eventually, results forthcoming from the Generation R Study have to contribute to the development of strategies for optimizing health and healthcare for pregnant women and children.

The Generation R Study: Design and cohort profile

The Generation R Study is a population-based prospective cohort study from fetal life until young adulthood. The study is designed to identify early environmental and genetic causes of normal and abnormal growth, development and health from fetal life until young adulthood. The study focuses on four primary areas of research: (1) growth and physical development; (2) behavioral and cognitive development; (3) diseases in childhood; and (4) health and healthcare for pregnant women and children. In total, 9778 mothers with a delivery date from April 2002 until January 2006 were enrolled in the study. Of all eligible children at birth, 61% participate in the study. Data collection in the prenatal phase included physical examinations, questionnaires, fetal ultrasound examinations and biological samples. In addition, more detailed assessments are conducted in a subgroup of 1232 pregnant women and their children. The children form a prenatally recruited birth-cohort that will be followed until young adulthood. Eventually, results forthcoming from the Generation R Study have to contribute to the development of strategies for optimizing health and healthcare for pregnant women and children.

Fatty acid composition of human milk in atopic Danish mothers

BACKGROUND

Atopic dermatitis has been related to a disturbed metabolism of polyunsaturated fatty acids (PUFAs).

OBJECTIVE

We tested whether the PUFA composition of breast milk differs significantly between mothers with atopic dermatitis, mothers with other types of atopy, and nonatopic mothers. We also investigated whether differences in diet can explain possible observed differences.

DESIGN

Mothers with current or previous asthma (n = 396) were divided into 3 groups according to history of atopic dermatitis and allergic rhinitis. Breast-milk samples were collected from 314 women approximately 3 wk after delivery. The habitual diet of the women was assessed with food-frequency questionnaires in the 25th week of gestation (n = 207). Breast-milk samples and simultaneous dietary data from 14 nonatopic mothers were used for comparison.

RESULTS

Compared with the milk of nonatopic mothers, that of atopic mothers had significantly higher concentrations of 22:5n-6 and lower concentrations of 20:5n-3; moreover, 20:4n-6/20:5n-3, 22:5n-6/22:6n-3, and long-chain n-3 PUFA/18:3n-3 were shifted toward n-6 PUFA and 18:3n-3 in nonatopic and atopic mothers, respectively. No differences in breast-milk PUFA composition were evident between the subject groups. The diets of the groups differed only slightly with respect to protein intake. However, the PUFA composition of the breast milk was associated with diet and time of milk sampling, and the above difference in milk PUFAs disappeared when those factors were taken into account.

CONCLUSION

Our data do not support the possibility that the fatty acid composition of breast milk is affected by atopic dermatitis or atopy in general, because most differences in breast-milk PUFA composition appear to be explained by the diet.

Stillbirth and slow metabolizers of caffeine: comparison by genotypes

BACKGROUND

Cytochrome P4501A2 (CYP1A2) and N-acetyltransferase 2 (NAT2) are key enzymes in the metabolism of caffeine. The polymorphism of these genes facilitates the detection of fast and slow metabolizers, and if caffeine is causally related to stillbirth, we expect slow metabolizers to have a higher risk of stillbirth at any given intake of caffeine. Gluthatione S-transferase alpha1 (GSTA1) may also be active in the metabolism of caffeine as it conjugates glutathione to aromatic amines. Our study, therefore, included analyses of the association between GSTA1 and stillbirth.

METHODS

A nested case non-case study among women who participated in the Danish National Birth Cohort: 142 cases of singleton stillbirths and 157 controls of singleton live births.

RESULTS

Slow oxidizer status (CYP1A2), slow acetylator status (NAT2), and low activity of GSTA1 were not individually associated with the risk of stillbirth [odds ratio (OR) = 1.06, 95% confidence interval (95% CI) 0.67-1.67, OR = 0.95, 95% CI 0.60-1.51, and OR = 1.42, 95% CI 0.88-2.28, respectively]. We did, however, observe that subjects with a combination of slow CYP1A2, slow NAT2, and low GSTA1 genes had almost a 2-fold risk of stillbirth compared with subjects with other combinations of genotypes.

CONCLUSIONS

We found no link between any single genotype and the risk of stillbirth. An association between a combination of genotypes and stillbirth was discovered. Caffeine may be causally related to stillbirth, but larger studies using Mendelian randomization are needed to verify this.

The association between atopy and factors influencing folate metabolism: is low folate status causally related to the development of atopy?

BACKGROUND

Deficiency of folate has been associated with several disorders characterized by enhanced activation of the cellular immune system (non-allergic th1 type immune response). Whether folate status is also associated with atopic disease (allergic th2 type immune response) is unknown. We aimed at examining the association between atopy and markers of impaired folate metabolism, i.e. MTHFR(C677T) genotype, plasma total homocysteine, and dietary intakes of methionine, folates, and vitamins B12, B6, and B2.

METHODS

Cross-sectional population-based study of 1,671 male and female residents of Copenhagen County, Denmark, aged 30-60 years participating in a health examination during 1999-2001. Atopy was defined as positive levels of specific IgE against a panel of inhalant allergens. MTHFR(C677T) genotype was determined by PCR followed by restriction fragment length polymorphism analyses. Total homocysteine was measured by fluorescent polarization immunoassay. Dietary vitamin intakes were estimated from a semi-quantitative food frequency questionnaire.

RESULTS

The prevalence of atopy was associated with MTHFR(C677T) genotype. TT individuals had a significantly higher risk of atopy compared with CC/CT individuals [odds ratio 1.76, 95% confidence interval (95% CI) 1.19-2.60]. Additionally, gene-diet interaction effects were identified. Dietary markers were negatively associated with risk of atopy in persons with the TT genotype. Total homocysteine was not related to atopy (odds ratio per 5 mumol/l = 1.12, 95% CI 0.98-1.29).

CONCLUSIONS

The results suggest that an impaired folate metabolism may be causally related to the development of atopy.

Maternal fish oil supplementation during lactation does not affect blood pressure, pulse wave velocity, or heart rate variability in 2.5-y-old children

Maternal (n-3) PUFA deficiency is associated with higher blood pressure (BP) later in life in rat offspring, and early intake of (n-3) PUFA in formula-fed infants was shown to modify later BP. BP, heart rate (HR), and heart rate variability (HRV) are affected by dietary (n-3) PUFA in adults. In this study, we investigated whether fish oil (FO) supplementation of lactating mothers could modify BP, pulse wave velocity (PWV), and HRV in their children after 2 y. Mothers with low fish intake were randomly assigned to FO or olive oil (OO) supplementation for the first 4 mo after delivery. A reference group of mothers with a high habitual fish intake (HFI) was also followed. At the follow-up study at 2.5 y of age, BP and PWV were measured, and electrocardiograms were recorded for 0.5 h. FO supplementation significantly increased RBC levels of long-chain (n-3) PUFA of the 4 mo-old children, but at 2.5 y, the FO and OO groups did not differ. BP, PWV, HR, and HRV also did not differ among the groups. However, for all 3 groups, the children's intake of (n-3) PUFA at 2.5 y was negatively correlated with mean arterial pressure after adjustment for outdoor temperature (r = -0.245, P = 0.04). In conclusion, maternal FO supplementation had no overall effect on BP, PWV, or HRV of the children, indicating that (n-3) PUFA intake of Danish mothers may be sufficient in this sense. However, children's dietary intake of (n-3) PUFA might have a beneficial effect on BP in childhood.

Do women give the same information on binge drinking during pregnancy when asked repeatedly?

OBJECTIVE

To study if pregnant women give the same answers to questions on frequency and timing of binge drinking when asked more than once during and after pregnancy.

DESIGN

Cohort study.

SETTING

The Danish National Birth Cohort.

SUBJECTS

The study is based on 76 307 pregnant women with repeated information on binge drinking during the early part of pregnancy and 8933 pregnant women with information on binge drinking during pregnancy weeks 30-36, obtained while pregnant and 6 months after delivery.

RESULTS

More women reported binge drinking, if the interview took place close to the period in question. As the report of binge drinking was highest in the first of two interviews referring to the same period, as well as women who participated in the first interview in pregnancy week 12 or earlier reported more binge drinking compared to women who participated in the interview later in pregnancy.

CONCLUSIONS

Self-reported information on binge drinking is more frequently under-reported when the recall period is long. To improve the validity of data on binge drinking, future birth cohorts should obtain information several times during pregnancy.

Occupational Exposure to Pesticides and Pregnancy Outcomes in Gardeners and Farmers: A Study Within the Danish National Birth Cohort

OBJECTIVE

We conducted a follow-up study to examine whether exposure to pesticides during pregnancy had an adverse effect on pregnancy outcomes among Danish gardeners and farmers.

METHODS

Using data from the National Birth Cohort in Denmark, we identified 226 pregnancies of gardeners and 214 pregnancies of farmers during 1997 through 2003. Work activities and exposure to pesticides were reported in an interview (around 16 weeks of gestation). Totally, 62,164 other workers in the cohort served as a reference group. Pregnancy outcomes were obtained by linkage to the national registers. Cox regression was applied to analyze late fetal loss and congenital malformations, and logistic regression was used to analyze preterm birth and small for gestational age.

RESULTS

There were no significant differences in the studied pregnancy outcomes between gardeners or farmers and all other workers, except for an increased risk of very preterm birth for gardeners and a favorable birth weight for farmers. With the exception of biologic approach used in gardening, neither work activities nor exposure to pesticides showed a significant increased risk of adverse birth outcomes among gardeners or farmers.

CONCLUSIONS

Our data suggest little effect of occupational exposures to pesticides on pregnancy outcomes among gardeners or farmers in Denmark. The results may not apply to other countries.

General obstetrics: Fish oil in various doses or flax oil in pregnancy and timing of spontaneous delivery: a randomised controlled trial

OBJECTIVES

To test the earlier suggested hypothesis that intake of long-chain n-3 fatty acids from fish oil may delay the timing of spontaneous delivery and to test if alpha-linolenic acid, provided as flax oil capsules, shows the same effect.

DESIGN

Randomised controlled trial including women reporting low dietary fish intake. The women were allocated in the proportions of 1:1:1:1:1:1:2 into six treatment groups and a control group, respectively, from week 17-27 of gestation. The treatment groups received fish oil, in various doses, or flax oil, and the control group did not receive any treatment.

SETTING

The Danish National Birth Cohort.

SAMPLE

A total of 3098 women allocated into six treatment groups and one control group.

METHODS

The six intervention groups were offered fish oil capsules in doses of 0.1, 0.3, 0.7, 1.4 and 2.8 g of eicosapentaenoic acid and docosahexaenoic acid per day or 2.2 g of alpha-linolenic acid (ALA) per day from week 17-27 of gestation until delivery.

MAIN OUTCOME MEASURES

Timing of spontaneous delivery.

RESULTS

No differences in timing of spontaneous delivery was detected in the fish oil groups or the flax oil group, compared with the control group. The difference in timing of spontaneous delivery in the group receiving the highest fish oil dose compared with the control group was 0.8 days (95% CI: -2.3 to 1.0). Only a minority of the women in the intervention groups took capsules until delivery.

CONCLUSION

Possible explanations for these findings include no true effect of n-3 fatty acids on spontaneous delivery or a quick-acting effect not detectable in this trial.