Socio-economic disparities in pregnancy outcome: why do the poor fare so poorly?

Vitamins C and E and the risks of preeclampsia and perinatal complications

BACKGROUND

Supplementation with antioxidant vitamins has been proposed to reduce the risk of preeclampsia and perinatal complications, but the effects of this intervention are uncertain.

METHODS

We conducted a multicenter, randomized trial of nulliparous women between 14 and 22 weeks of gestation. Women were assigned to daily supplementation with 1000 mg of vitamin C and 400 IU of vitamin E or placebo (microcrystalline cellulose) until delivery. Primary outcomes were the risks of maternal preeclampsia, death or serious outcomes in the infants (on the basis of definitions used by the Australian and New Zealand Neonatal Network), and delivering an infant whose birth weight was below the 10th percentile for gestational age.

RESULTS

Of the 1877 women enrolled in the study, 935 were randomly assigned to the vitamin group and 942 to the placebo group. Baseline characteristics of the two groups were similar. There were no significant differences between the vitamin and placebo groups in the risk of preeclampsia (6.0 percent and 5.0 percent, respectively; relative risk, 1.20; 95 percent confidence interval, 0.82 to 1.75), death or serious outcomes in the infant (9.5 percent and 12.1 percent; relative risk, 0.79; 95 percent confidence interval, 0.61 to 1.02), or having an infant with a birth weight below the 10th percentile for gestational age (8.7 percent and 9.9 percent; relative risk, 0.87; 95 percent confidence interval, 0.66 to 1.16).

CONCLUSIONS

Supplementation with vitamins C and E during pregnancy does not reduce the risk of preeclampsia in nulliparous women, the risk of intrauterine growth restriction, or the risk of death or other serious outcomes in their infants. (Controlledtrials.com number, ISRCTN00416244.).

The role of mediating factors in the association between social deprivation and low birth weight in Germany

This study examines whether the association between social inequalities and low birth weight (LBW) (occurring in both pre- and full-term births) in Germany can be explained by several potentially confounding factors. These include maternal age, occupational status, marital status, nationality, employment status, smoking, prenatal care, psychosocial stress, obesity, short stature, short inter-pregnancy interval, chronic conditions, and several obstetrical risk factors such as pregnancy induced hypertension. We also examined how the risk for LBW varies over time within each socioeconomic group. We analyzed routinely collected perinatal data on singletons born in the federal state of Lower Saxony, Germany, in 1990, 1995, and 1999 (n = 182,444). After adjustment for all potentially confounding factors in multivariate logistic regression models, working class women, unemployed women, single mothers, and women over 39 years of age were at increased risk for pre- and full-term LBW infants. Migrant status was not related to LBW. We examined variations in the risk for LBW over time within groups, using the 1990 birth cohort as the referent group for the 1995 and 1999 birth cohorts. Compared to 1990, in 1999 women aged 19-34 years, housewives, unemployed women, women of German nationality and women with partners had higher risks for pre- and full-term LBW infants; the eldest subgroup had lower risks for LBW after adjustment for confounding factors. The factors we examined partly explain the social inequalities in LBW occurring in pre- and full-term infants. The subgroups with higher rates of LBW in 1999 compared to 1990, included women experiencing childbirth in an optimal stage of life or in a privileged social context. Public health policies in Germany should target social inequalities contributing to the aetiology of LBW and to the factors that result in increased LBW rates.

Low psychosocial resources during early pregnancy are not associated with prolonged labour

OBJECTIVES

To examine if a low level of psychosocial resources in early pregnancy is associated with the occurrence of prolonged labour.

STUDY DESIGN

A cross sectional study of 644 women expecting their first child. Participants were asked to complete a questionnaire at their first antenatal visit, measuring psychosocial resources defined as social network and support, work-related psychosocial factors, control of daily life and health characteristics. Outcome was prolonged labour at the end of the pregnancy.

RESULTS

A low level of psychosocial resources was not associated with prolonged labour. The majority of women reported that the degree of support was high in early pregnancy.

CONCLUSIONS

A perceived low level of psychosocial resources in early pregnancy did not increase the risk of prolonged labour at the subsequent delivery.

Explaining the social gradient in smoking in pregnancy: Early life course accumulation and cross-sectional clustering of social risk exposures in the 1958 British national cohort

Smoking in pregnancy is a major determinant of low birthweight and a range of adverse infant health outcomes. There is a well-established social gradient in smoking in pregnancy in the US and northern Europe. Social gradients in health-related behaviours may result from longitudinal accumulation and cross-sectional clustering of social risk exposures. There is, however, no published confirmation of this explanation in empirical data with smoking in pregnancy as the outcome. This study aimed to test the effects of longitudinal accumulation and cross-sectional clustering of social risk exposures on smoking in pregnancy using data on the first pregnancies of 3163 female members of the 1958 British national cohort. Social class at birth and aged 11 years was used to create three dichotomous variables representing cumulative social class (both manual, one manual and one non-manual, both non-manual) early in the lifecourse. Cross-sectional clustering of social risk was represented by four dichotomous variables created from combinations of maternal age (<20 vs. 20+), own social class (manual vs. non-manual) and educational attainment (low vs. other). Cumulative social class in early childhood was associated with smoking in pregnancy in bivariate analysis but not after adjustment for cross-sectional clustering of social risk exposures. However, women who had been in the manual social groups at birth and 11 years were at increased risk of cross-sectional clustering of social risk exposures around pregnancy suggesting a pathway from early lifecourse risk exposure to social risk factors associated with a high risk of smoking in pregnancy. These findings suggest that the social gradient in smoking in pregnancy results from longitudinal accumulation and cross-sectional clustering of social risk exposures. Interventions aimed at reducing social inequalities in smoking in pregnancy need to account for cumulative and cross-sectionally clustered effects of social risk exposures.

Ethnic differences in total and cause-specific infant mortality in The Netherlands

We examined ethnic differences in infant mortality and the contribution of several explanatory variables. Data of Statistics Netherlands from 1995 to 2000 were studied (1,178,949 live borns). Proportional hazard analysis was used to show ethnic differences in total and cause-specific infant mortality. Obstetric, demographic and -geographical variables, and socio-economic status were considered as possible determinants. The four major ethnic minority groups showed an elevated risk of infant mortality, ranging from 1.28 in Turkish infants to 1.50 in Antillean/Aruban infants. In the early neonatal period, risks were elevated for Surinamese (hazard ratio [HR] 1.48, 95% confidence intervals [CI] 1.23, 1.78) and Antilleans/Arubans (HR 1.43, 95% CI 1.06, 1.92). In the post-neonatal period, risks were only elevated for Turkish (HR 2.20, 95% CI 1.80, 2.69) and Moroccan infants (HR 2.06, 95% CI 1.67, 2.55). Surinamese and Antillean/Aruban infants had an elevated risk of dying from perinatal causes (HR 1.62, 95% CI 1.33, 1.98 and 1.69, 95% CI 1.24, 2.29 respectively), Turkish and Moroccan infants had an elevated risk of dying from congenital anomalies (HR 1.42, 95% CI 1.16, 1.73 and 1.46, 95% CI 1.20, 1.79 respectively). Inequalities as a result of socio-economic position and demographic factors, such as marital status and maternal age, partially explain the ethnic differences in infant mortality. We conclude that ethnic minority groups in The Netherlands have a higher infant mortality than the native population, which in part seems preventable by reducing inequalities in socio-economic status. Marital status and age of the mother are important other risk factors of infant mortality.

Socio-demographic factors associated with smoking and smoking cessation among 426,344 pregnant women in New South Wales, Australia

Background

This study explores the socio-demographic characteristics of pregnant women who continue to smoke during the pregnancy, and identifies the characteristics of the smokers who were likely to quit smoking during the pregnancy period.

Methods

This was secondary analysis of the New South Wales (NSW) Midwives Data Collection (MDC) 1999–2003, a surveillance system covering all births in NSW public and private hospitals, as well as home births. Bivariate and multiple logistic regression analyses were performed to explore the associations between socio-demographic characteristics and smoking behaviour during pregnancy.

Results

Data from 426,344 pregnant women in NSW showed that 17.0% continued to smoke during pregnancy. The smoking rate was higher among teenage mothers, those with an Aboriginal (indigenous) background, and lower among more affluent and overseas-born mothers. This study also found that unbooked confinements, and lack of antenatal care in the first trimester were strongly associated with increased risk of smoking during pregnancy. About 4.0% of the smoking women reported they may quit smoking during their pregnancy. Findings showed that mothers born overseas, of higher socio-economic status, first time mothers and those who attended antenatal care early showed an increased likelihood of smoking cessation during pregnancy. Those who were heavy smokers were less likely to quit during pregnancy.

Conclusion

Although the prevalence of smoking during pregnancy has been declining, it remains a significant public health concern. Smoking cessation programs should target the population subgroups of women at highest risk of smoking and who are least likely to quit. Effective antismoking interventions could reduce the obstetric and perinatal complications of smoking in pregnancy.

Social position affects bone mass in childhood through opposing actions on height and weight

We studied relationships between social position of the mother in pregnancy and bone mass of the child at age 9.9 years. The tendency for social position to increase bone area and bone mass through a positive influence on height was opposed by a negative effect of social position on weight and fat mass.

INTRODUCTION

Evidence that social factors influence skeletal growth raises the possibility that bone mass acquisition in childhood is socially determined.

MATERIALS AND METHODS

To clarify the role of social factors in bone mass acquisition in childhood, we studied relationships between these variables in the Avon Longitudinal Study of Parents and Children (ALSPAC). Measures of the mother's social position during pregnancy were linked to DXA results obtained at age 9.9 years in 6,702 children. Linear regression analyses were carried out after adjusting for age and gender. Because social position may affect height and weight of the child, analyses were repeated after adjusting for these additional variables.

RESULTS

Measures of social position in pregnancy were unrelated to total body BMC in analyses adjusted for age and gender alone. However, after adjusting for height, which was positively related to social position, a strong negative association was observed between BMC and housing tenure (p < 0.001), maternal education (p < 0.001), paternal education (p < 0.001), and social class (p < 0.001). Similar results were obtained for bone area. After adjusting for weight as well as height, an association between social position and BMC and bone area was no longer observed. Hence, social position seems to exert opposing height- and weight-dependent effects on BMC and bone area in childhood. In further analyses, we found that adjusting for fat mass of the child led to similar results to those obtained with weight.

CONCLUSIONS

Social position in childhood seems to be positively related to bone mass acquisition in childhood as a consequence of enhanced gain in height (i.e., longitudinal growth). However, this influence is counteracted by the tendency for increased fat deposition in those from a lower social position to increase bone area, presumably reflecting the stimulation of appositional bone growth.

Birth outcomes and prenatal exposure to ozone, carbon monoxide, and particulate matter: results from the Children's Health Study

Exposures to ambient air pollutants have been associated with adverse birth outcomes. We investigated the effects of air pollutants on birth weight mediated by reduced fetal growth among term infants who were born in California during 1975-1987 and who participated in the Children's Health Study. Birth certificates provided maternal reproductive history and residence location at birth. Sociodemographic factors and maternal smoking during pregnancy were collected by questionnaire. Monthly average air pollutant levels were interpolated from monitors to the ZIP code of maternal residence at childbirth. Results from linear mixed-effects regression models showed that a 12-ppb increase in 24-hr ozone averaged over the entire pregnancy was associated with 47.2 g lower birth weight [95% confidence interval (CI), 27.4-67.0 g], and this association was most robust for exposures during the second and third trimesters. A 1.4-ppm difference in first-trimester carbon monoxide exposure was associated with 21.7 g lower birth weight (95% CI, 1.1-42.3 g) and 20% increased risk of intrauterine growth retardation (95% CI, 1.0-1.4). First-trimester CO and third-trimester O3 exposures were associated with 20% increased risk of intrauterine growth retardation. A 20-microg/m3 difference in levels of particulate matter < or = 10 microm in aerodynamic diameter (PM10) during the third trimester was associated with a 21.7-g lower birth weight (95% CI, 1.1-42.2 g), but this association was reduced and not significant after adjusting for O3. In summary, O3 exposure during the second and third trimesters and CO exposure during the first trimester were associated with reduced birth weight.

Antioxidants for preventing pre-eclampsia

BACKGROUND

Oxidative stress has been proposed as a key factor involved in the development of pre-eclampsia. Supplementing women with antioxidants during pregnancy may help to counteract oxidative stress and thereby prevent or delay the onset of pre-eclampsia.

OBJECTIVES

To determine the effectiveness and safety of any antioxidant supplementation during pregnancy and the risk of developing pre-eclampsia and its related complications.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group Trials Register (June 2004) and the Cochrane Central Register of Controlled Trials (The Cochrane Library, Issue 3, 2004).

SELECTION CRITERIA

All randomised and quasi-randomised trials comparing one or more antioxidants with either placebo or no antioxidants during pregnancy for the prevention of pre-eclampsia, and trials comparing one or more antioxidants with another, or with other interventions.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trials for inclusion, data extraction and trial quality. Data were double-entered into the Review Manager software.

MAIN RESULTS

Seven trials involving 6082 women are included in this review. The largest trial (5021 women) was quasi-random and only three of the seven included trials were rated high quality. Supplementing women with any antioxidants during pregnancy compared with control or placebo was associated with a 39% reduction in the risk of pre-eclampsia (relative risk (RR) 0.61, 95% confidence intervals (CI) 0.50 to 0.75, seven trials, 6082 women). Women receiving antioxidants compared with control or placebo also had a reduced risk of having a small-for-gestational-age infant (RR 0.64, 95% CI 0.47 to 0.87, three trials, 634 women), their infants had a greater mean birthweight (weighted mean difference 91.83 g, 95% CI 11.55 to 172.11, three trials, 451 women), but they were more likely to give birth preterm (RR 1.38, 95% CI 1.04 to 1.82, three trials, 583 women). There were insufficient data for reliable conclusions about possible effects on any other outcomes.

AUTHORS' CONCLUSIONS

These results should be interpreted with caution, as most of the data come from poor quality studies. Nevertheless, antioxidant supplementation seems to reduce the risk of pre-eclampsia. There also appears to be a reduction in the risk of having a small-for-gestational-age baby associated with antioxidants, although there is an increase in the risk of preterm birth. Several large trials are ongoing, and the results of these are needed before antioxidants can be recommended for clinical practice.

Adverse Perinatal Outcomes Among Interracial Couples in the United States

OBJECTIVE

We examined the association between parental race and stillbirth and adverse perinatal and infant outcomes.

METHODS

We conducted a retrospective cohort analysis using the 1995-2001 linked birth and infant death files that are composed of live births and fetal and infant deaths in the United States. The study included singleton births delivered at 20 or more weeks of gestation with a fetus weighing 500 g or more (N = 21,005,786). Parental race was categorized as mother white-father white, mother white-father black, mother black-father white, and mother black-father black. Multivariable logistic regression analysis was performed to examine the association between parental race and risks of stillbirth (at > or = 20 weeks), small for gestational age (defined as birth weight < 5th and < 10th percentile for gestational age), and early neonatal (< 7 days), late neonatal (7-27 days), and postneonatal (28-364 days) mortality. All analyses were adjusted for the confounding effects of maternal age, education, trimester at which prenatal care began, parity, marital status, and smoking during pregnancy.

RESULTS

Although risks varied across parental race categories, stillbirth was associated with a higher-than-expected risk for interracial couples: mother white-father black, relative risk (RR) 1.17 (95% confidence interval [CI] 1.10-1.26) and mother black-father white, RR 1.37 (95% CI 1.21-1.54) compared with mother white-father white parents. The RR for stillbirth was even higher among mother black-father black parents (RR 1.67, 95% CI 1.62-1.72). The overall patterns of association for small for gestational age births (< 5th and < 10th percentile) and early neonatal mortality were similar to those seen for stillbirth.

CONCLUSION

There is an increased risk of adverse perinatal outcomes for interracial couples, including stillbirth, small for gestational age infants, and neonatal mortality.

LEVEL OF EVIDENCE

II-2.

Birth Weight of Offspring and Subsequent Cardiovascular Mortality of the Parents

BACKGROUND

Restricted fetal growth has been associated with increased blood pressure, insulin resistance, and cardiovascular disease in later life. These associations may be due to processes during fetal development with long-term consequences for metabolic and cardiovascular function (the fetal origins hypothesis). However, it has also been hypothesized that common genetic factors could underlie both restricted fetal development and disease risk (the fetal insulin hypothesis).

METHODS

We have investigated associations between offspring size at birth and parental mortality in a record linkage study including all 783,814 children born in Sweden between 1973 and 1980. The deaths of 10,368 mothers and 22,807 fathers had been recorded by date and causes of death. Data were analyzed using Cox proportional hazards regression models, with parents' age as the time axis.

RESULTS

Offspring birth weight (adjusted for gestational age) was inversely associated with all-cause mortality and cardiovascular mortality in the parents, with weaker associations for fathers than for mothers. The inverse association between birth weight and cardiovascular disease mortality was greatest for parents who died at younger ages. Cancer and alcohol-related causes of death were also related to offspring birth weight. A sensitivity analysis suggests that confounding by smoking is unlikely to entirely explain the associations.

CONCLUSION

Associations between offspring birth characteristics and parents' mortality could, at least in part, reflect genetic factors that influence both birth weight and cardiovascular disease risk.

Risk factors for intrauterine growth restriction: a comparison between two Brazilian cities

In Brazil, similar intrauterine growth restriction (IUGR) rates were observed between cities with distinct levels of socioeconomic development, challenging the current knowledge that higher rates of IUGR would necessarily be observed in poorer areas than in wealthier ones. Ribeirão Preto, a city located in the most developed area in Brazil, showed an IUGR rate of 18% in 1994, whereas this rate was 18.5% in 1997/1998 in São Luis, located in one of the poorest areas in the country. The objective of this study was to compare risk factors for IUGR in these two cities and to identify factors that are responsible for this unexpected lack of difference between the rates. Using data from two birth cohorts, including 2839 neonates who were from Ribeirão Preto and born in 1994 and 2439 neonates who were from São Luis and born in 1997/1998, a multivariable analysis was conducted to assess changes in the risk for IUGR in the poorer city compared with the wealthier one in a combined model, adjusting for some risk factors for IUGR. The wealthier city showed higher rates of maternal smoking, attendance in the private sector, and obstetric interventions than the less developed one. Differences in maternal smoking and obstetric interventions were possibly responsible for the similarity of the rates between cities. It seems that early detection of IUGR followed by cesarean section in the wealthier city is associated with increased low birth weight and IUGR rates but reduced stillbirth and infant mortality rates.

Risk factors for spontaneous preterm birth among Aboriginal and non-Aboriginal women in Manitoba

In the province of Manitoba, the incidence of preterm birth has been increasing and the rate is higher among Aboriginal than non-Aboriginal women. The purpose of this study was to identify risk factors for spontaneous preterm birth in Manitoba women, and to compare risk factors among Aboriginal and non-Aboriginal women. A case-control study was performed at two tertiary care hospitals in Winnipeg, Manitoba, Canada from October 1999 to December 2000. Cases delivered a live singleton infant at < 37 weeks gestation (n = 226; 36% Aboriginal), while controls delivered between 37 and 42 weeks gestation (n = 458; 38% Aboriginal). An interview was conducted with each subject on the postpartum unit, and information was collected from the health record. Using stratified analyses to control for race/ethnicity, several risk factors for preterm birth had a uniform effect measure across strata, while others demonstrated heterogeneity. After adjusting for other maternal characteristics in a multivariable logistic regression model, significant risk factors for all women included previous preterm birth, two or more previous spontaneous abortions, vaginal bleeding after 12 weeks gestation, gestational hypertension, antenatal hospitalisation, and prelabour rupture of membranes. In addition, potentially modifiable risk factors included low weight gain during pregnancy and inadequate prenatal care for all women, and high levels of perceived stress for Aboriginal women. These modifiable risk factors lend themselves to public health interventions, and should be targeted in future prevention efforts.

Large social disparities in spontaneous preterm birth rates in transitional Russia

OBJECTIVE

This study estimated the effect of maternal sociodemographic, obstetric and lifestyle factors on the risk of spontaneous preterm birth in a Russian town.

METHODS

All women with singleton pregnancies registered at prenatal care centres in Severodvinsk in 1999 comprised the cohort for this study (n=1559). Analysis was based on spontaneous live singleton births at the maternity home (n=1103). Multivariable logistic regression was applied to quantify the effect of the studied factors on the risk of preterm birth. Differences in gestation duration were studied using multiple linear regression.

RESULTS

In total, 5.6% of all spontaneous births were preterm. Increased risks of preterm delivery were found in women with lower levels of education and in students. Placental complications, stress and a history of fetal death in previous pregnancies were also associated with elevated risks for preterm delivery. Smoking, hypertension and multigravidity were associated with reduced length of pregnancy in metric form.

CONCLUSION

In addition to medical risk factors, social factors are important determinants of preterm birth in transitional Russia. Large disparities in preterm birth rates may reflect the level of inequalities in transitional Russia. Social variations in pregnancy outcomes should be monitored.

Antiplatelet agents for prevention of pre-eclampsia and its consequences: a systematic review and individual patient data meta-analysis

BACKGROUND: There is now good evidence that antiplatelet agents (principally low dose aspirin) prevent pre-eclampsia, a leading cause of morbidity and mortality for pregnant women and their babies. A Cochrane Review identified moderate, but clinically important, reductions in the relative risks of pre-eclampsia (19%), preterm birth (7%) and perinatal mortality (16%) in women allocated antiplatelets, rather than placebo or no antiplatelet.Uncertainty remains, however, about whether some women (in terms of risk) benefit more than others, what dose of aspirin is best and when in pregnancy treatment should ideally start. Rather than undertake new trials, the best way to answer these questions is to utilise existing individual patient data from women enrolled in each trial. METHODS/DESIGN: Systematic review with meta-analysis based on individual patient data. This involves the central collection, validation and re-analysis of thoroughly checked data from individual women in all the available randomised trials.The objective is to confirm that antiplatelet agents, given during pregnancy, will reduce the incidence of pre-eclampsia. The review will then determine the size of this effect, and whether antiplatelets delay the onset of pre-eclampsia or its impact on important outcomes for women and their babies. It will also explore whether the effect of antiplatelets differs by womens' risk profile; when commenced during pregnancy; and/or by dose. DISCUSSION: The PARIS (Perinatal Antiplatelet Review of International Studies) Collaboration has been formed to undertake the review. This will be the first individual patient data review in the perinatal field. Final results should be available by 2006-7.

Prevalence and Predictors of Inadequate Prenatal Care: A Comparison of Aboriginal and Non-Aboriginal Women in Manitoba

OBJECTIVE

Despite the importance of prenatal care, there are no national data and limited provincial data on use of prenatal care by women in Canada, nor is there much information on racial/ethnic disparities in access to prenatal care. This study describes and compares the prevalence and predictors of inadequate prenatal care among Aboriginal and non-Aboriginal women giving birth in Manitoba.

METHODS

Data were obtained from interviews with 652 postpartum women who delivered a live singleton infant in 2 tertiary hospitals in Winnipeg, Manitoba. We identified inadequate prenatal care, using the Kessner Adequacy of Prenatal Care Index. We used stratified analysis to describe effect-measure modification for predictors of inadequate prenatal care among the Aboriginal and non-Aboriginal subgroups. We conducted a multivariable logistic regression analysis for the total sample.

RESULTS

A significantly higher proportion of Aboriginal women (15.7%) than non-Aboriginal women (3.6%) received inadequate prenatal care. After controlling for other factors, significant predictors of inadequate prenatal care included low income, low self-esteem, high levels of perceived stress, and Aboriginal background.

CONCLUSION

Women who do not receive adequate prenatal care are more likely to live in poverty, experience highly stressed lives, have low levels of self-esteem, and be Aboriginal. Efforts to improve the provision of prenatal care should be directed toward these women. Racial/ethnic disparities in use of prenatal care need to be addressed.

Prematurity and fetal growth restriction

Assessment of the growth status of the fetus and neonate is an essential component of perinatal care. It requires a distinction to be made between physiological and pathological factors, and the prediction of the optimal growth that a baby can achieve in a normal, uncomplicated pregnancy. Such an individually customised standard can now be easily calculated by computer: it needs to be accurately dated, individually adjusted for physiological characteristics, exclude pathological factors such as smoking, and be based on a fetal weight trajectory derived from normal term pregnancies. Application of a customised standard to calculate the growth status of preterm babies gives us freshly insights into the causes of prematurity. Fetal growth restriction is seen as a strongly associated factor, which is often present before the onset of spontaneous preterm labour. This raises the question whether, in many instances, the initiation of parturition should be seen as a fetal adaptive response aimed at escaping an unfavourable intrauterine environment. These concepts have implications for the understanding of the pathophysiology of preterm labour, as well as its clinical management.

Preterm birth and maternal country of birth in a French district with a multiethnic population

OBJECTIVES

This analysis explores the association between preterm birth and maternal country of birth in a French district with a multiethnic population.

DESIGN

Prospective observational study.

SETTING

District of Seine-Saint-Denis in France

POPULATION

48,746 singleton live births from a population-based birth register between October 1998 and December 2000.

METHODS

We compare preterm birth rates by mother's country of birth controlling for demographic and obstetric factors as well as insurance coverage and timing of initiation of antenatal care.

MAIN OUTCOME MEASURES

Overall preterm birth rates and preterm birth rates by timing of delivery (<33 weeks versus 33-36 weeks of gestation), mode of onset (spontaneous or indicated preterm birth) and the presence of hypertension in pregnancy.

RESULTS

Women born in Northern Africa, Southern Europe and South/East Asia did not have higher preterm birth rates than women born in continental France. Rates were significantly higher for women born in the overseas French districts in the Caribbean and Indian Ocean and Sub-Saharan Africa. Excess risk was greatest for early preterm births, medically indicated births and preterm births associated with hypertension.

CONCLUSIONS

Patterns of preterm birth with relation to timing, mode of onset and medical complications among of Afro-Caribbean origin should be confirmed in future research.

The association of maternal growth and socio-economic measures with infant birthweight in four ethnic groups

BACKGROUND

Both maternal socio-economic status (SES) and growth measures are themselves interrelated and are also related to infant birthweight. The objective of this study is to compare the relative importance of such maternal measures as determinants of birthweight of female infants-the prospective mothers of the next generation.

METHODS

The study base was derived from a population-based multiethnic intergenerational cohort: the Washington State Intergenerational Cohort. Infants of mothers from four ethnic groups were included: non-Hispanic Whites, African Americans, Native Americans, and Hispanics. We generated simple, partial, and multiple correlation coefficients to investigate the association between birthweight and the maternal growth and SES measures.

RESULTS

While there were slight differences among the ethnic groups, generally each of three maternal pre-conceptional growth measures-birthweight, stature, and pre-pregnant weight-was a stronger predictor of female infant birthweight than were each of the five maternal SES factors-age, parity, marital status, educational attainment, and prenatal care onset. After accounting for the proportion of variation in birthweight explained by the maternal growth measures and maternal smoking, the addition of the five SES variables added relatively little to the prediction of infant birthweight. The maximal multiple correlation coefficients (R2) yield values ranging from 9.5% to 12.8%.

CONCLUSIONS

A mother's growth before pregnancy is a stronger predictor of infant birthweight than is her current socio-economic circumstance. Since the mother's growth must have been influenced by the socio-economic circumstances of her family of upbringing, this further highlights the intergenerational contribution on a woman's reproductive success.

Dietary composition of pregnant women is related to size of the baby at birth

The fetal origins theory of adult disease suggests that term infants who are small for their gestational age have an increased susceptibility to chronic disease in adulthood as a consequence of physiologic adaptations to undernutrition during fetal life. Consistent evidence for an influence of women's dietary composition during pregnancy on growth of their babies is lacking, despite robust effects in animal experiments. We undertook a prospective observational study of 557 women aged 18-41 y, living in Adelaide, South Australia. Diet was assessed in early and late pregnancy using an FFQ. In early pregnancy, medians for energy intake, the proportion of energy derived from protein and from carbohydrate were 9.0 MJ, 17 and 48%, respectively. In late pregnancy the corresponding medians were 9.2 MJ, 16 and 49%. In early pregnancy, the percentage of energy derived from protein was positively associated with birth weight (P = 0.02) and placental weight (P = 0.07), independently of energy intake and weight gain during pregnancy, and after adjustment for potential confounders, including maternal age, parity, and smoking. Effects were stronger among women (n = 429) who had reliable data, based on prespecified criteria including the plausibility of dietary data when referenced against estimated energy expenditure. In addition, for this subgroup, the percentage of energy from carbohydrate in early and late pregnancy was negatively associated with ponderal index of the baby, and a specific effect of protein from dairy sources was identified. These data support the proposition that maternal dietary composition has an effect on fetal growth. Maternal diet in Western societies may therefore be important for the long-term health of the child.

Birth weight is inversely associated with coronary heart disease in post-menopausal women: findings from the British women's heart and health study

OBJECTIVES

(1) To assess the association between birth weight and coronary heart disease (CHD) risk in a cohort of post-menopausal women, (2) to determine the combined effects of birth weight and adult body mass index on CHD, (3) to assess the role of insulin resistance as a mediating factor in the associations.

DESIGN

Cross sectional survey.

SETTING

23 British towns.

PARTICIPANTS

1394 women aged 60-79 years.

MAIN OUTCOME MEASURES

coronary heart disease (n = 199 cases).

RESULTS

Birth weight was inversely associated with CHD: age and survivor status of participant's mother adjusted odds ratio (95% confidence intervals) per 1 standard deviation (0.80 kg) increase in birth weight was 0.84 (0.72 to 0.97). This association strengthened to 0.80 (0.68 to 0.93) with further adjustment for adult body mass index, but there was no evidence of an interaction between birth weight and adult body mass index (p = 0.61). The association was not confounded by childhood or adulthood socioeconomic position or by adult smoking status of the participant. Adjustment for components of the insulin resistance syndrome attenuated the association to 0.87 (0.72 to 1.03).

CONCLUSIONS

Intrauterine exposures that affect fetal growth also affect future adult CHD risk. The inverse association between birth weight and CHD may in part be mediated via insulin resistance.

Early origins of the gradient: the relationship between socioeconomic status and infant mortality in the United States

Although relationships between social conditions and health have been documented for centuries, the past few decades have witnessed the emergence of socioeconomic gradients in health and mortality in most developed countries. These gradients indicate that health improves, although decreasingly so, at higher levels of socioeconomic status. To minimize problems with reverse causality, I tested competing hypotheses for observed socioeconomic gradients for infant mortality outcomes. I found no support for the income-inequality hypothesis and negligible support for the occupational-grade hypothesis. The results indicate that absolute material conditions are the most important determinants of socioeconomic effects on the risk of infant mortality and that while poverty has the most pronounced effect on risk, income is decreasingly salutary across the majority of the mortality gradient.

Socioeconomic gradients and low birth-weight: empirical and policy considerations

OBJECTIVE

To examine whether socioeconomic status (SES) gradients emerge in health outcomes as early as birth and to examine the magnitude, potential sources, and explanations of any observed SES gradients.

DATA SOURCES

The National Maternal and Infant Health Survey conducted in 1988.

STUDY DESIGN

A multinomial logistic regression of trichotomized birth-weight categories was conducted for normal birth-weight (2,500-5,500 grams), low birth-weight (LBWT; < 2,500 grams), and heavy birth-weight (> 5,500 grams). Key variables included income, education, occupational grade, state-level income inequality, and length of participation in Women-Infants-Children (WIC) for pregnant mothers.

PRINCIPAL FINDINGS

A socioeconomic gradient for low birth-weight was discovered for an adjusted household income measure, net of all covariates in the unrestricted models. A gross effect of maternal education was explained by maternal smoking behaviors, while no effect of occupational grade was observed, net of household income. There were no significant state-level income inequality effects (Gini coefficient) for any of the models. In addition, participation in WIC was discovered to substantially flatten income gradients for short-term participants and virtually eliminate an income gradient among long-term participants.

CONCLUSIONS

Although a materialist explanation for early-life SES gradients seems the most plausible (vis-à-vis psychosocial and occupational explanations), more research is needed to discover potential interventions. In addition, the notion of a monotonic gradient in which income is salutary across the full range of the distribution is challenged by these data such that income may cease to be beneficial after a given threshold. Finally, the success of WIC participation in flattening SES gradients argues for either: (a) the experimental efficacy of WIC, or (b) the biasing selection characteristics of WIC participants; either conclusion suggests that interventions or characteristics of participants deserves further study as a potential remedy for socioeconomic disparities in early-life health outcomes such as LBWT.

Early mortality among triplets in the United States: black-white disparity

OBJECTIVE

In this study, we sought to estimate the black-white gap in early mortality among triplets.

STUDY DESIGN

This was a retrospective cohort study on triplets delivered in the United States from 1995 to 1997. We computed relative risks for early mortality among triplets born to black mothers using the generalized estimating equation framework.

RESULTS

There were 1317 black and 14,364 white triplets analyzed. Black triplets were twice as likely to have neonatal and infant mortality compared with whites (Odds ratio [OR], 2.00, 95% CI, 1.38-2.77; and OR, 2.20, 95% CI, 1.59-3.00, respectively). The widest disparity was observed postneonatally, with black triplets sustaining a level of risk almost 4-fold that of whites (OR, 3.60, 95% CI, 2.10-6.10). Stillbirth and perinatal mortality were comparable for both races.

CONCLUSION

Black-white disparity for early mortality among triplets was widest postneonatally. This finding bears important clinical and public health implications.

Risk factors for preterm births in São Luís, Maranhão, Brazil

Preterm birth continues to be one of the main causes of neonatal morbidity and mortality. The objective of the present study was to identify risk factors for preterm birth in São Luís, Maranhão, Brazil. The sample consisted of hospital births at 10 public and private hospitals from March 1, 1997 to February 28, 1998. A total of 2,443 live births were randomly selected, excluding multiple deliveries and stillbirths. Preterm birth rate in São Luís was 12.7%. Risk factors for preterm delivery were maternal age below 18 years, family income equal to or less than one minimum wage/ month, primiparity, vaginal delivery at a public hospital, single mothers (or living without a partner), and absence of prenatal care. The following factors remained associated with preterm birth after multivariate analysis to control for confounding: maternal age below 18 years (OR = 1.9), primiparity (OR = 1.5), and failure to appear for scheduled prenatal care visits (OR = 1.5).

Small-for-gestational-age births in the United States: an age-period-cohort analysis

BACKGROUND

During the last 2 decades, the rate of low birthweight has increased, as has the rate of preterm delivery, among both whites and blacks. Examination of causes for these secular trends has focused largely on changes in the distributions of maternal age and, less commonly, on birth cohort. Little is known as to how age, period, and birth cohort interact on trends in small births at term.

METHODS

The U.S. natality files were used to assess trends in term (>/=37 weeks gestation) small-for-gestational age (SGA) births for 7 5-year maternal age groups (15-19 through 45-49 years), 6 delivery periods (1975, 1980, 1985, 1990, 1995, and 2000), and 12 5-year maternal birth cohorts (1926-1930 through 1981-1985). SGA births were defined as sex-specific birthweight below the 10th percentile for gestational age based on 1995 livebirths in the United States. Logistic regression models were fit to determine the independent effects of age, delivery period, and birth cohort on term SGA trends, separately for blacks and whites.

RESULTS

Between 1975 and 2000, term SGA births declined by 23% (from 21% to 16%) among blacks and by 27% (from 12% to 9%) among whites. Term SGA births declined with increasing age up to 30-34 years, but increased among older women. Within strata of maternal age, the risk also declined with later maternal birth cohorts, among both blacks and whites. The strongest influence on SGA trends was from maternal age, followed by maternal birth cohort, and lastly by delivery period. In general, for any combination of age, period, and birth cohort, blacks showed 1.5- to 2-fold higher rates of term SGA than whites.

CONCLUSIONS

The persistence of strong maternal age effects on risk of term SGA births suggests that the effect of age is at least partly the result of biologic factors. Term SGA trends were generally consistent for blacks and whites, although the magnitude of difference in the risks for combinations of age, period, or mother's birth cohort was higher among blacks than whites.

Pesquisa sobre mortalidade perinatal no Brasil: revisão da metodologia e dos resultados

A mortalidade perinatal persiste como relevante evento em saúde pública, demandando estudos epidemiológicos, tanto para definir sua magnitude e variações temporais, como para identificar seus determinantes e apontar as intervenções adequadas. Existem ainda questões conceituais e metodológicas controversas, gerando heterogeneidade nos estudos e prováveis vieses. No Brasil, nos últimos anos, desponta uma produção crescente sobre o tema, principalmente no Sudeste e Sul. Foram revistos 24 artigos de 1996 a 2003, focalizando: definições e classificações utilizadas, fontes de dados, desenhos de estudo, formas de aferição das variáveis, modelos de análise estatística e principais resultados. A revisão mostrou a progressiva utilização de bancos de dados informatizados, principalmente o SINASC e o SIM, o pequeno número de estudos sobre natimortalidade, a incorporação ainda incipiente das classificações de causas e a discordância em relação a alguns fatores de risco.

Young maternal age and preterm birth

The association between young maternal age and preterm birth (PTB) remains controversial. In some studies the association disappeared after controlling for socio-economic and reproductive factors, thus indicating that social disadvantage rather than biological factors may be the explanation. However, in other studies the association persisted after adjustment. The relation between young maternal age and PTB was studied in a city located in Brazil, an underdeveloped country, where the prevalence of teenage pregnancy was high, 29%. A systematic sampling of 2541 hospital births, stratified by hospital, was performed in São Luís, Northeast Brazil, from March 1997 to February 1998. The risks of PTB for infants born to two groups of young mothers (<18 and 18-19 years) were calculated with and without adjustment for confounding factors (family income, marital status, mode of delivery, parity, health insurance, and short maternal stature) in a logistic regression model, using mothers 25-29 years of age as the reference group. In the unadjusted analysis, the risk of PTB was higher for mothers < 18 years [odds ratio (OR) = 2.42, 95% confidence interval (CI) 1.64, 3.57]. Those aged 18 or 19 years were not at a higher risk of PTB (OR = 0.89, 95% CI 0.58, 1.38). After adjustment, the risk of PTB for mothers < 18 years was lower but remained significant after controlling for confounding (OR = 1.70, 95% CI 1.11, 2.60). After performing a stratified analysis according to parity, the risk of PTB among very young primiparae (<18 years) remained significant (OR = 1.77, 95% CI 1.02, 3.08), whereas the risk among non-primiparous adolescents was not significantly higher than the risk among mothers in the reference group. This suggests that the association between young maternal age and PTB may have a biological basis or an artifactual explanation (errors in gestational age estimation may be more common among very young mothers) or may be due to residual confounding.

Social trends in singleton births and birth weight in Wirral residents, 1990-2001

OBJECTIVE

To examine social trends in the number of singleton births and birth weight in an English health district between 1990 and 2001, using an area based deprivation index.

DESIGN

Analysis of routinely collected hospital data.

SETTING

Wirral Health District in north west England.

PARTICIPANTS

All 48 452 live births to Wirral residents from 1990 to 2001.

MAIN OUTCOME MEASURES

Birth numbers, birth weight, and standard deviation score for birth weights for singleton births. Townsend material deprivation scores derived from postcodes.

RESULTS

The number of singleton births fell by 28% over the 12 years. The fall in the least deprived Townsend quartile (45%) was more than triple that in the most deprived quartile (gamma = 0.045; 95% confidence interval (CI) = 0.036 to 0.054; p < 0.001). Over the study period, the mean birth weight in the least deprived Townsend quartile was 141 g higher than in the most deprived quartile. There was a highly significant association between the standard deviation score for birth weight and Townsend quartile (tau-b = -0.062; 95% CI = -0.068 to -0.055; p < 0.001). Numbers of low birth weight babies in the least deprived quartile fell disproportionately compared with those from the most deprived quartile (gamma = 0.17; 95% CI = 0.09 to 0.25; p < 0.001).

CONCLUSION

The reduction in birth rate in the Wirral was significantly less in the most deprived districts. This was accompanied by related differences in mean birth weight and the number of low birth weight babies, indicating increasing social inequality in birth trends. Previously described social inequity in birth weight and the number of low birth weight babies continues in the north west of England.

Birthweight and perinatal mortality: paradoxes, social class, and sibling dependencies

BACKGROUND

Birthweight distributions among second-born infants depend on the birthweights of older siblings, with implications for weight-specific perinatal mortality. We wanted to study whether these relations were explained by socioeconomic levels, and to study time trends in a situation with decreasing perinatal mortality rates.

METHODS

Births in the Norwegian Medical Birth Registry from 1967 to 1998 were linked to their mothers through their national identification numbers. The study population was 546 688 mothers with at least two singletons weighing >/==" BORDER="0">500 g at birth. Weight-specific perinatal mortality for second-born siblings in families with first-born siblings in either the highest or the lowest birthweight quartile was analysed. Maternal education and cohabitation status were used as measures of socioeconomic level.

RESULTS

For all 500-g categories below 3500 g, mortality rates were significantly higher among second-born infants with an older sibling in the highest rather than the lowest weight quartile. This pattern was the same across three educational levels. The exclusion of preterm births did not change the effect pattern. A comparison of perinatal mortality among second siblings in terms of relative birthweight (z-scores) showed a reversal of the relative risks, although these were only significantly different from unity for the smallest infants. Conclusion The crossover in weight-specific perinatal mortality for second siblings by weight of first sibling is largely independent of socioeconomic level, and is not weakened by the decreasing perinatal mortality rates in the population over time. Family data should be taken into consideration when evaluating the risk of adverse pregnancy outcome relating to weight.

Is periodontitis associated with an increased risk of coronary heart disease and preterm and/or low birth weight births?

The objective of this systematic review was to determine whether periodontal disease is associated with an increased risk for coronary heart disease (CHD) and preterm and/or low birth weight deliveries (PLBW). A literature search was performed to identify cross-sectional, case-control, and cohort studies as well as clinical trials addressing different aspects of periodontal disease (clinical, microbial, immunological) and clinical outcomes of CHD or PLBW. The periodontitis-CHD association was evaluated in eight cohort, four case-control- and four cross-sectional studies. Meta-analysis was not performed due to the extensive heterogeneity of the studies, particularly with regard to periodontitis measures, which varied from full mouth probing assessments to questionnaires. Percentage-wise, 50% of the cohort studies (4/8), 75% of the case-control studies (3/4) and 50% of the cross-sectional studies (2/4) reported a significant association between clinical measures of periodontitis and CHD (excess risk ranged from 0 to 3.3-fold). The periodontitis-PLBW association was evaluated in one cohort and two case-control studies. The cohort study as well as one of the two case-control studies reported a significant association between periodontitis and PLBW (odds ratios 4.4-7.9). From two additional case-control studies microbiological data could be extracted. Bacteroides forsythus was found to be associated with PLBW in both studies. In conclusion, the evidence linking periodontitis with an increased risk for CHD and PLBW is limited. There is a clear need for new, well designed observational and intervention studies to confirm the thus far observed associations, explore the validity of the associations in diverse populations, establish whether they are causal in nature and determine potential benefits of periodontal intervention in reducing the risk for these conditions.

Nutrition before birth, programming and the perpetuation of social inequalities in health

The need to explain social inequalities in health has led to the theory that chronic disease is due, in part, to a legacy of adverse experiences in early life. Epidemiological studies show consistently that individuals who are small at birth have an increased risk of cardiovascular disease in adulthood. There is growing consensus that this association reflects a causal relationship and is not simply the product of bias or confounding. The concept of programming is invoked as the biological mechanism; birth size is thus a proxy for fetal programming. Recent findings suggest that fetal programming interacts with the post-birth environment. The adverse exposures that are thought to underlie and potentiate programming cluster in socially patterned ways, thus creating substantial inequalities in health. Experiments in animals demonstrate that nutritional interventions before or during pregnancy can produce programming phenomena in the offspring, sometimes without an impact on birth size. However, the extent to which maternal nutrition contributes to programming in contemporary developed countries is uncertain.

Preventing low birth weight: is prenatal care the answer?

OBJECTIVES

To review the evidence of effectiveness of prenatal care for preventing low birth weight (LBW).

METHODS

We reviewed original research, systematic reviews, meta-analyses and commentaries for evidence of effectiveness of the three core components of prenatal care--risk assessment, health promotion and medical and psychosocial interventions--for preventing the two constituents of LBW: preterm birth and intrauterine growth restriction (IUGR).

RESULTS

Clinical risk assessment will fail to identify the majority of pregnancies at risk for preterm delivery or IUGR. While biophysical and biochemical modalities appear promising, their cost-effectiveness has not been demonstrated, nor can their routine use be recommended in the absence of effective interventions. Smoking cessation programs appear to be modestly effective. There is insufficient evidence to conclude a benefit for nutrition interventions, work counseling or preterm birth education. Only antenatal corticosteroid therapy has demonstrated a clear benefit in the tertiary prevention of preterm delivery. Interventions for which there is insufficient evidence to conclude a benefit include bed rest, hydration, sedation, cerclage, progesterone supplementation, antibiotic treatment, tocolysis without concomitant use of corticosteroids, thyrotropin-releasing hormone, psychosocial support and home visitation. Additionally, there is a paucity of evidence supporting the effectiveness of prenatal interventions, such as low-dose aspirin, bed rest, maternal hyperoxygenation, plasma volume expansion and antenatal fetal assessment, in preventing IUGR or its associated morbidity and mortality.

CONCLUSIONS

Neither preterm birth nor IUGR can be effectively prevented by prenatal care in its present form. Preventing LBW will require reconceptualization of prenatal care as part of a longitudinally and contextually integrated strategy to promote optimal development of women's reproductive health not only during pregnancy, but over the life course.

The epidemiology of adverse pregnancy outcomes: an overview

This paper provides an overview of the occurrence, etiology and temporal trends of adverse pregnancy outcomes. Disparities between developed and developing countries are highlighted for maternal mortality, infant mortality, stillbirth and low birth weight. The higher rate of low birth weight in developing countries is primarily due to intrauterine growth restriction rather than preterm birth. Much of the excess intrauterine growth restriction is caused by short maternal stature, low prepregnancy body mass index and low gestational weight gain (due to low energy intake). No important contribution has been established for micronutrient intake, nor have different fetal growth trajectories been demonstrated to reflect the timing of exposure to nutritional or other etiologic factors. Infant mortality has declined substantially over time both in developed and developing countries despite no decline (and even an increase) in low birth weight. Several developed countries have reported a temporal increase in fetal growth in infants born at term, a reduction in stillbirth rates and prevention of neural tube defects. More progress is required, however, in understanding the etiology and prevention of preterm birth.

Racial and ethnic disparities in birth outcomes: a life-course perspective

BACKGROUND

In the United States, Black infants have significantly worse birth outcomes than do White infants. The cause of these persisting racial disparities remains unexplained. Most extant studies focus on differential exposures to protective and risk factors during pregnancy, such as current socioeconomic status, maternal risky behaviors, prenatal care, psychosocial stress, or perinatal infections. These risk factors during pregnancy, however, do not adequately account for the disparities.

METHODS

We conducted a literature review for longitudinal models of health disparities, and presented a synthesis of two leading models, using a life-course perspective. Traditional risk factors during pregnancy are then reexamined within their life-course context. We conclude with a discussion of the limitations and implications of the life-course perspective for future research, practice, and policy development.

RESULTS

Two leading longitudinal models of health disparities were identified and discussed. The early programming model posits that exposures in early life could influence future reproductive potential. The cumulative pathways model conceptualizes decline in reproductive health resulting from cumulative wear and tear to the body's allostatic systems. We propose a synthesis of these two models, using the life-course perspective. Disparities in birth outcomes are the consequences of differential developmental trajectories set forth by early life experiences and cumulative allostatic load over the life course.

CONCLUSIONS

Future research on racial disparities in birth outcomes needs to examine differential exposures to risk and protective factors not only during pregnancy, but over the life course of women. Eliminating disparities requires interventions and policy development that are more longitudinally and contextually integrated than currently prevail.

Preventable feto-infant mortality: application of a conceptual framework for perinatal health surveillance to Manitoba perinatal outcomes

BACKGROUND

Perinatal health surveillance systems have lacked conceptual frameworks to translate data into information for policy and program planning. This paper demonstrates the application of a conceptual framework in the analysis of feto-infant mortality data in the province of Manitoba.

METHODS

Fetal and infant deaths were categorized according to a two-dimensional framework of birthweight and age-at-death, and grouped into four broad categories of contributors to perinatal health: Maternal Health, Maternal Care, Newborn Care, and Infant Care. Birth Weight Proportionate Mortality Rates (BWPMR) were calculated for each of the four categories, and preventable "excess" feto-infant mortality was estimated through comparisons to a benchmark sub-population.

RESULTS

Between 1985 and 1998, feto-infant mortality declined from 12.3 to 9.8 deaths per 1000 births in Manitoba. Much of this decline occurred in the Newborn Care category; there were only slight declines in deaths attributed to Maternal Health and Infant Care factors. Comparison of the feto-infant mortality rate to the benchmark rate revealed an excess of 3.46 deaths per 1000 births, an "opportunity gap" of 33%. Substantial regional variations in feto-infant mortality rates were observed.

SUMMARY

Application of this conceptual framework provided useful information to aid in policy and program planning. As the greatest excess feto-infant mortality was observed in the Maternal Health and Infant Care categories, attention to the broader determinants of health which influence these categories will be required.

The treatment of parental height as a biological factor in studies of birth weight and childhood growth

Parental height is frequently treated as a biological variable in studies of birth weight and childhood growth. Elimination of social variables from multivariate models including parental height as a biological variable leads researchers to conclude that social factors have no independent effect on the outcome. This paper challenges the treatment of parental height as a biological variable, drawing on extensive evidence for the determination of adult height through a complex interaction of genetic and social factors. The paper firstly seeks to establish the importance of social factors in the determination of height. The methodological problems associated with treatment of parental height as a purely biological variable are then discussed, illustrated by data from published studies and by analysis of data from the 1958 National Childhood Development Study (NCDS). The paper concludes that a framework for studying pathways to pregnancy and childhood outcomes needs to take account of the complexity of the relation between genetic and social factors and be able to account for the effects of multiple risk factors acting cumulatively across time and across generations. Illustrations of these approaches are given using NCDS data.

Socioeconomic status and preterm birth: New Zealand trends, 1980 to 1999

BACKGROUND

While a number of countries have reported rising preterm birth rates over the past two decades, none has examined the effects of socioeconomic status on preterm birth at a national level.

AIM

To document the changing incidence of preterm birth in New Zealand over the past 20 years and to determine whether particular socioeconomic or ethnic subsections of the population have contributed disproportionately to the changes seen.

METHODS

Birth registration data routinely available from the New Zealand Health Information Service were analysed for the period 1980-99. Information for a total of 1 079 478 singleton live births was linked by Domicile Code to the New Zealand Deprivation Index, a small area index of deprivation.

RESULTS

Singleton preterm birth rates rose by 37.2% during the 20 year period, from 4.3% in 1980 to 5.9% in 1999. Rates increased by 71.9% among those living in the most affluent areas, but by only 3.5% among those living in the most deprived areas, resulting in the disappearance of a socioeconomic gradient in preterm birth that had existed during the early 1980s.

CONCLUSIONS

This study challenges traditional thinking on the associations between socioeconomic status and preterm birth. Further research is necessary if the changes that have occurred in New Zealand over the past 20 years are to be fully understood.

Maternal periodontitis and prematurity. Part I: Obstetric outcome of prematurity and growth restriction

Oral Conditions and Pregnancy (OCAP) is a 5-year prospective study of pregnant women designed to determine whether maternal periodontal disease contributes to the risk for prematurity and growth restriction in the presence of traditional obstetric risk factors. Full-mouth periodontal examinations were conducted at enrollment (prior to 26 weeks gestational age) and again within 48 hours postpartum to assess changes in periodontal status during pregnancy. Maternal periodontal disease status at antepartum, using a 3-level disease classification (health, mild, moderate-severe) as well as incident periodontal disease progression during pregnancy were used as measures of exposures for examining associations with the pregnancy outcomes of preterm birth by gestational age (GA) and birth weight (BW) adjusting for race, age, food stamp eligibility, marital status, previous preterm births, first birth, chorioamnionitis, bacterial vaginosis, and smoking. Interim data from the first 814 deliveries demonstrate that maternal periodontal disease at antepartum and incidence/progression of periodontal disease are significantly associated with a higher prevalence rate of preterm births, BW < 2,500 g, and smaller birth weight for gestational age. For example, among periodontally healthy mothers the unadjusted prevalence of births of GA < 28 weeks was 1.1%. This was higher among mothers with mild periodontal disease (3.5%) and highest among mothers with moderate-severe periodontal disease (11.1%). The adjusted prevalence rates among GA outcomes were significantly different for mothers with mild periodontal disease (n = 566) and moderate-severe disease (n = 45) by pair-wise comparisons to the periodontally healthy reference group (n = 201) at P = 0.017 and P < 0.0001, respectively. A similar pattern was seen for increased prevalence of low birth weight deliveries among mothers with antepartum periodontal disease. For example, there were no births of BW < 1000 g among periodontally healthy mothers, but the adjusted rate was 6.1% and 11.4% for mild and moderate-severe periodontal disease (P = 0.0006 and P < 0.0001), respectively. Periodontal disease incidence/progression during pregnancy was associated with significantly smaller births for gestational age adjusting for race, parity, and baby gender. In summary, the present study, although preliminary in nature, provides evidence that maternal periodontal disease and incident progression are significant contributors to obstetric risk for preterm delivery, low birth weight and low weight for gestational age. These studies underscore the need for further consideration of periodontal disease as a potentially new and modifiable risk for preterm birth and growth restriction.

Birth weight and cognitive function at age 11 years: the Scottish Mental Survey 1932

AIMS

To examine the relation between birth weight and cognitive function at age 11 years, and to examine whether this relation is independent of social class.

METHODS

Retrospective cohort study based on birth records from 1921 and cognitive function measured while at school at age 11 in 1932. Subjects were 985 live singletons born in the Edinburgh Royal Maternity and Simpson Memorial Hospital in 1921. Moray House Test scores from the Scottish Mental Survey 1932 were traced on 449 of these children.

RESULTS

Mean score on Moray House Test increased from 30.6 at a birth weight of <2500 g to 44.7 at 4001-4500 g, after correcting for gestational age, maternal age, parity, social class, and legitimacy of birth. Multiple regression showed that 15.6% of the variance in Moray House Test score is contributed by a combination of social class (6.6%), birth weight (3.8%), child's exact age (2.4%), maternal parity (2.0%), and illegitimacy (1.5%). Structural equation modelling confirmed the independent contribution from each of these variables in predicting cognitive ability. A model in which birth weight acted as a mediator of social class had poor fit statistics.

CONCLUSION

In this 1921 birth cohort, social class and birth weight have independent effects on cognitive function at age 11. Future research will relate these childhood data to health and cognition in old age.

A new and improved population-based Canadian reference for birth weight for gestational age

BACKGROUND

Existing fetal growth references all suffer from 1 or more major methodologic problems, including errors in reported gestational age, biologically implausible birth weight for gestational age, insufficient sample sizes at low gestational age, single-hospital or other non-population-based samples, and inadequate statistical modeling techniques.

METHODS

We used the newly developed Canadian national linked file of singleton births and infant deaths for births between 1994 and 1996, for which gestational age is largely based on early ultrasound estimates. Assuming a normal distribution for birth weight at each gestational age, we used the expectation-maximization algorithm to exclude infants with gestational ages that were more consistent with 40-week births than with the observed gestational age. Distributions of birth weight at the corrected gestational ages were then statistically smoothed.

RESULTS

The resulting male and female curves provide smooth and biologically plausible means, standard deviations, and percentile cutoffs for defining small- and large-for-gestational-age births. Large-for-gestational age cutoffs (90th percentile) at low gestational ages are considerably lower than those of existing references, whereas small-for-gestational-age cutoffs (10th percentile) postterm are higher. For example, compared with the current World Health Organization reference from California (Williams et al, 1982) and a recently proposed US national reference (Alexander et al, 1996), the 90th percentiles for singleton males at 30 weeks are 1837 versus 2159 and 2710 g. The corresponding 10th percentiles at 42 weeks are 3233 versus 3086 and 2998 g.

CONCLUSIONS

This new sex-specific, population-based reference should improve clinical assessment of growth in individual newborns, population-based surveillance of geographic and temporal trends in birth weight for gestational age, and evaluation of clinical or public health interventions to enhance fetal growth. fetal growth, birth weight, gestational age, preterm birth, postterm birth.

The contribution of maternal smoking to preterm birth, small for gestational age and low birthweight among Aboriginal and non-Aboriginal births in South Australia

OBJECTIVES

To determine the contribution of maternal smoking to preterm birth (< 37 weeks' gestation), small for gestational age (SGA, birthweight < 10th percentile for gestational age) and low birthweight (< 2500 g) among Aboriginal and non-Aboriginal births in South Australia.

DESIGN

Retrospective cohort analysis of population-based perinatal data.

SETTING

The State of South Australia, population 1.5 million.

PARTICIPANTS

36059 women (of whom 851 were Aboriginal women) who had singleton births in 1998-1999.

MAIN OUTCOME MEASURES

Relative risks and population-attributable risks of preterm birth, SGA and low birthweight from smoking in the second half of pregnancy, by age and Aboriginality.

RESULTS

Aboriginal women had a higher rate of smoking in pregnancy than non-Aboriginal women (57.8% v 24.0% at the first antenatal visit) and high rates for all age groups, while the rates decreased with age among non-Aboriginal women. Heavy smoking increased with age, and Aboriginal women were heavier smokers. Women who smoked had elevated relative risks of preterm birth (1.64), SGA (2.28) and low birthweight (2.52), and all these showed a dose-response relationship. Among Aboriginal (versus non-Aboriginal) births, population-attributable risks were significantly higher for SGA (48% v 21%, and 59% for births to Aboriginal teenagers), low birthweight (35% v 23%) and preterm birth (20% v 11%).

CONCLUSIONS

Health promotion programs, with a focus on smoking cessation and reducing uptake of smoking, need to be implemented in an appropriate cultural context, especially among young Aboriginal women. Such a program is being developed in South Australia.