Maternal pre-pregnancy body mass index and risk of preterm birth: a collaboration using large routine health datasets

BACKGROUND

Preterm birth (PTB) is a leading cause of child morbidity and mortality. Evidence suggests an increased risk with both maternal underweight and obesity, with some studies suggesting underweight might be a greater factor in spontaneous PTB (SPTB) and that the relationship might vary by parity. Previous studies have largely explored established body mass index (BMI) categories. Our aim was to compare associations of maternal pre-pregnancy BMI with any PTB, SPTB and medically indicated PTB (MPTB) among nulliparous and parous women across populations with differing characteristics, and to identify the optimal BMI with lowest risk for these outcomes.

METHODS

We used three UK datasets, two USA datasets and one each from South Australia, Norway and Denmark, together including just under 29 million pregnancies resulting in a live birth or stillbirth after 24 completed weeks gestation. Fractional polynomial multivariable logistic regression was used to examine the relationship of maternal BMI with any PTB, SPTB and MPTB, among nulliparous and parous women separately. The results were combined using a random effects meta-analysis. The estimated BMI at which risk was lowest was calculated via differentiation and a 95% confidence interval (CI) obtained using bootstrapping.

RESULTS

We found non-linear associations between BMI and all three outcomes, across all datasets. The adjusted risk of any PTB and MPTB was elevated at both low and high BMIs, whereas the risk of SPTB was increased at lower levels of BMI but remained low or increased only slightly with higher BMI. In the meta-analysed data, the lowest risk of any PTB was at a BMI of 22.5 kg/m2 (95% CI 21.5, 23.5) among nulliparous women and 25.9 kg/m2 (95% CI 24.1, 31.7) among multiparous women, with values of 20.4 kg/m2 (20.0, 21.1) and 22.2 kg/m2 (21.1, 24.3), respectively, for MPTB; for SPTB, the risk remained roughly largely constant above a BMI of around 25-30 kg/m2 regardless of parity.

CONCLUSIONS

Consistency of findings across different populations, despite differences between them in terms of the time period covered, the BMI distribution, missing data and control for key confounders, suggests that severe under- and overweight may play a role in PTB risk.

The Danish implementation study on response to pregnancy complications, MAMAACT

Differential incidence and severity of pregnancy complications are likely important contributing factors to the increased risk of poor pregnancy outcomes among ethnic minority women in Europe. To address this issue, the MAMAACT trial has been developed based on a thorough mixed methods needs assessment and co-creation process, feasibility tested, now implemented in a nationwide complex intervention. The overall aim of the Danish MAMAACT trial is to reduce ethnic and social disparity in stillbirth and newborns' health by improved management of pregnancy complications. The overall target group is all pregnant women, and the specific target group is women of non-Western origin. The hypothesis of MAMAACT is that improved communication between pregnant women and midwives regarding body symptoms that need prompt reaction will improve perinatal health among these vulnerable groups. The intervention consists of postgraduate training of midwives in intercultural communication and a smart phone application and a leaflet, both in six different languages. The app and leaflet target the women and explain the most serious warning signs of pregnancy complications and how to respond to them.

MAMAACT is implemented and evaluated in a randomized controlled cluster trial and 10 maternity wards consist the intervention groups, while nine maternity wards are the control groups. The evaluation is a mixed method evaluation focusing on understanding the mechanisms of change, how context at both maternity ward level as well as in the everyday life of women affects the implementation, and finally if effects on health literacy of the women and perinatal health of the children can be documented.

Differences in stillbirth and infant mortality by maternal country of birth and descent in Denmark

International studies have reported inequalities in stillbirth and infant death among ethnic minority groups compared to the host population. The same tendencies have been reported in Denmark. We investigated differences in the risk of stillbirth and infant death among offspring of immigrants and descendants in Denmark, compared to the risk among women of Danish origin.

The population-based register study included all live births and stillbirths with gestational age ≥ 22 weeks delivered by women of Danish origin, immigrant women and descendants in Denmark in the period 2005-2016. The study population was restricted to deliveries by women of Danish origin and country groups of immigrants and descendants with more than 2000 deliveries during the study period (n = 792 705).

Logistic regression analysis adjusted for year of birth was used to estimate odds ratios (OR) with 95 % confidence intervals (CI) of the association between maternal country of birth and country of descent and respectively stillbirth and infant mortality.

Immigrant mothers from Turkey, Iraq, Somalia, Pakistan, Afghanistan, Syria and Iran had a statistically significant elevated OR of stillbirth compared to women of Danish origin; adjusted OR`s ranging 1.45-2.93. Danish-born women with respectively Turkish (OR 1.44, 95 % CI 1.00-2.07) and Pakistani descent (OR 2.32, 95 % CI 1.50-3.60) had an increased risk of stillbirth similar to the one among immigrant women with the same origin. For infant death, we found increased OŔs among immigrant women from Turkey (OR 1.76, 95 % CI 1.28-2.40), Somalia (OR 1.84, 95 % CI 1.31-2.58), Lebanon (OR 1.63, 95 % CI 1.03-2.60) and Pakistan (OR 2.85, 95 % CI 2.05-3.96). Only women of Pakistani descent (2.22, 95 % CI 1.28-3.86) had a statistically significant increased risk of infant death.

These findings show substantial differences in stillbirth and infant death according to maternal country of birth and descent in Denmark during the first decades of the 21st century.

Associations between maternal socioeconomic position and psoriasis: a cohort study among the offspring of the Danish National Birth Cohort

BACKGROUND

The socioeconomic determinants of paediatric-onset psoriasis have not been previously investigated.

OBJECTIVE

To identify whether a social gradient exists for paediatric-onset psoriasis, using measures of maternal socioeconomic position.

METHODS

Data on paediatric-onset psoriasis from 36 003 Danish National Birth Cohort offspring were cross-linked with nationwide registry data on maternal age and three measures of maternal socioeconomic position: maternal educational attainment, maternal labour market attachment and equivalized household income. Univariable and multivariable logistic regression analyses were conducted to estimate the odds ratios (ORs) of psoriasis in the offspring, in cohort analyses for data from the year of enrolment and cross-sectional analyses from the year of the 11-year follow-up.

RESULTS

Maternal age at birth, maternal educational attainment and equivalized household income were inversely associated with psoriasis in the offspring. Low maternal educational attainment was associated with offspring psoriasis [adjusted OR 1·62, 95% confidence interval (CI) 1·20-2·18] after adjusting for maternal psoriasis and age in the cohort analysis. The crude OR of psoriasis in offspring of mothers in the highest quartile compared with mothers in the lowest quartile of equivalized household income was 0·57 (95% CI 0·43-0·76), and the adjusted OR was 0·59 (95% CI 0·44-0·80) after adjusting for maternal psoriasis and age. Similar results were observed for data on maternal socioeconomic position at enrolment and at follow-up.

CONCLUSIONS

A steep social gradient in paediatric-onset psoriasis was observed. Maternal socioeconomic position may play a role in early-life exposure to modifiable risk factors for psoriasis. Future studies may help to elucidate which biological factors mediate the social gradient observed in our study.

Fever and infections during pregnancy and psychosis-like experiences in the offspring at age 11. A prospective study within the Danish National Birth Cohort

BACKGROUND

Maternal exposures to fever and infections in pregnancy have been linked to subsequent psychiatric morbidity in the child. This study examined whether fever and common infections in pregnancy were associated with psychosis-like experiences (PLEs) in the child.

METHODS

A longitudinal study of 46 184 children who participated in the 11-year follow-up of the Danish National Birth Cohort was conducted. Pregnant women were enrolled between 1996 and 2002 and information on fever, genitourinary infections, respiratory tract infection, and influenza-like illness during pregnancy was prospectively collected in two interviews during pregnancy. PLEs were assessed using the seven-item Adolescent Psychotic-Like Symptom Screener in a web-based questionnaire completed by the children themselves at age 11.

RESULTS

PLEs were reported among 11% of the children. Multinomial logistic regression models with probability weights to adjust for potential selection bias due to attrition suggested that maternal fever, genitourinary infections and influenza-like illness were associated with a weak to moderate increased risk of subclinical psychosis-like symptoms in the offspring, whereas respiratory tract infections were not. No clear pattern was observed between the strengths of the associations and the timing of exposure, or the type of psychosis-like symptom.

CONCLUSIONS

In this study, maternal exposures to fevers and common infections in pregnancy were generally associated with a subtle excess risk of PLEs in the child. A more pronounced association was found for influenza-like illness under an a priori definition, leaving open the possibility that certain kinds of infections may constitute important risk factors.

Timing of motor milestones achievement and development of overweight in childhood: a study within the Danish National Birth Cohort

BACKGROUND

Overweight may hinder achievement of gross motor milestones and delayed achievement of milestones may increase the risk of later overweight for reasons involving physical activity and the building of lean body mass.

OBJECTIVE

To investigate whether increased birth weight and body mass index (BMI) at 5 months is associated with the achievement of the ability to sit up and walk and whether delayed achievement of these milestones is associated with overweight at age 7 years.

METHODS

We used data from the Danish National Birth Cohort on 25,148 children born between 1998 and 2003. Follow-up took place from 2003 to 2010. Mean age at follow-up was 7.04 years. We used logistic and linear regression analyses.

RESULTS

Birth weight and BMI at 5 months were marginally associated with earlier achievement of the ability to sit up and walk (regression coefficients between -0.027 months; [CI -0.042; -0.013] and -0.092 months [CI -0.118; -0.066]). Age in months of sitting and walking were not associated with overweight at age 7 years (ORs between 0.97 [CI 0.95-1.00] and 1.00 [CI 0.96-1.04]). Later achievement of sitting and walking predicted lower BMI at age 7 years (ln-BMI -z-scores between -0.023 [CI -0.029; -0.017] and -0.005 [CI -0.015; 0.005)).

CONCLUSIONS

All observed associations were of negligible magnitude and we conclude that birth weight or BMI at age 5 months and motor milestones appear largely independent of each other and that timing of achievement of motor milestones seems not to be associated with later overweight or increased BMI.

Prenatal exposure to alcohol, and gender differences on child mental health at age seven years

BACKGROUND

It remains uncertain whether exposure to lower doses of alcohol is damaging to the developing fetus. The present study aimed to investigate associations for boys and girls between prenatal exposure to binge drinking and lower doses of alcohol in pregnancy, and parent-reported behavioural and emotional development at age seven.

METHODS

This study used data from the Danish National Birth Cohort. Associations between cumulated alcohol exposure and binge drinking from full pregnancy and parent scores on the Strengths and Difficulties Questionnaire (SDQ) measured at age seven were investigated. The SDQ was used as continuous externalising/internalising scores, and as above/below cut-off for the specific scales of hyperactivity/inattention, conduct, emotional and peer problems. Inclusion criteria were information on alcohol exposure from three interviews, SDQ scores at age seven and being born full term (n=37 152).

RESULTS

Controlling for relevant confounders, small positive associations were observed between binge drinking and internalising (relative change in mean: 1.04-1.06), externalising scores (relative change in mean: 1.01-1.07), and conduct scores (OR 1.12 to 1.23) for boys. No associations were observed with lower doses of alcohol.

CONCLUSIONS

Exposure to binge drinking is weakly associated with impaired behavioural and emotional development measured at age seven. Large differences in background characteristics were observed between the groups defined by cumulated alcohol exposure, leaving the interpretations of findings uncertain.

Prevalence of Coxiella burnetii in women exposed to livestock animals, Denmark, 1996 to 2002

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Smoking and pregnancy-related pelvic pain

OBJECTIVE

To investigate possible associations between smoking and pregnancy-related pelvic pain.

DESIGN

Nested case-control study.

SETTING

Denmark 2000-2001.

POPULATION

The Danish National Birth Cohort.

METHODS

The women were interviewed twice in pregnancy and twice after childbirth. The first pregnancy interview provided information on smoking and possible confounding factors,whereas the first interview after birth addressed case identification.Cases (n = 2302) were defined on the basis of self-reported pelvic pain, and controls were selected among women who did not report pelvic pain (n = 2692). Logistic regression analysis was used to estimate associations between smoking and pelvic pain.

MAIN OUTCOME MEASURE

Pregnancy-related pelvic pain.

RESULTS

Compared with non-smokers, women who smoked during pregnancy had an adjusted odds ratio of 1.2 (1.0-1.4) for overall pelvic pain, similar to women who stopped smoking in early pregnancy 1.3 (1.1-1.7). The equivalent adjusted odds ratio for severe pelvic pain was 1.2 (1.0-1.5) for smokers, and 1.5 (1.2-1.9)for women who stopped smoking. Smoking intensity, measured as number of cigarettes smoked per day, was associated with pelvic pain in a dose-response pattern. Information about smoking was collected prospectively, which makes it unlikely that differential recall alone explains the results.

CONCLUSIONS

Smoking was associated with pregnancy-related pelvic pain, with a dose-response pattern between reported smoking intensity and pelvic pain. These findings suggest a possible new risk factor for a common ailment during pregnancy

Maternal age and fetal loss: population based register linkage study

OBJECTIVE

To estimate the association between maternal age and fetal death (spontaneous abortion, ectopic pregnancy, stillbirth), taking into account a woman's reproductive history.

DESIGN

Prospective register linkage study.

SUBJECTS

All women with a reproductive outcome (live birth, stillbirth, spontaneous abortion leading to admission to hospital, induced abortion, ectopic pregnancy, or hydatidiform mole) in Denmark from 1978 to 1992; a total of 634 272 women and 1 221 546 pregnancy outcomes.

MAIN OUTCOME MEASURES

Age related risk of fetal loss, ectopic pregnancy, and stillbirth, and age related risk of spontaneous abortion stratified according to parity and previous spontaneous abortions.

RESULTS

Overall, 13.5% of the pregnancies intended to be carried to term ended with fetal loss. At age 42 years, more than half of such pregnancies resulted in fetal loss. The risk of a spontaneous abortion was 8.9% in women aged 20-24 years and 74.7% in those aged 45 years or more. High maternal age was a significant risk factor for spontaneous abortion irrespective of the number of previous miscarriages, parity, or calendar period. The risk of an ectopic pregnancy and stillbirth also increased with increasing maternal age.

CONCLUSIONS

Fetal loss is high in women in their late 30s or older, irrespective of reproductive history. This should be taken into consideration in pregnancy planning and counselling.