Very and moderate preterm births: are the risk factors different?

Attachment and mother-infant interactions in dyads with infants born full-term, moderate-to-late preterm, and very-to-extreme preterm

BACKGROUND

The impact of prematurity status on attachment quality remains indeterminate. Some studies found no differences between infants born preterm (PT) and infants born full-term (FT), while other investigations present opposite results.

AIMS

We aim to contribute to this body of research by studying mother-infant interactive behaviors and quality of attachment in 3 independent samples: Full-Term (FT), Moderate-to-Late Preterm (MLPT) and Very-to-Extreme Preterm (VEPT).

STUDY DESIGN

This is a longitudinal laboratory study conducted from 3 to 12 months of age (corrected-age in the case of infants born PT).

SUBJECTS

The participants are 213 Portuguese infants (FT = 105; MLPT = 52; VEPT = 56) and their mothers.

OUTCOME MEASURES

Mother-infant interactive behavior was observed in free-play at 3 and 9 months (corrected-age). Infant attachment was observed in Strange Situation at 12 months.

RESULTS

Secure attachment is more prevalent in infants born FT, and ambivalent attachment is more prevalent in infants born VEPT. Infants with a secure attachment have higher gestational age and weight at birth. Infant and maternal interactive behavior quality is associated with attachment patterns and varies according to infant prematurity status. Last, the results indicate changes in maternal sensitivity and infant difficult behavior from 3 to 9 months of infant's age.

CONCLUSIONS

Our findings indicate that prematurity status impacts attachment quality. Changes in maternal and infant behavior from 3 to 9 months suggest a period of rapid non-linear development, supporting a transactional multilayered approach to the study of mother-infant relationship.

Preterm Birth and Small-for-Gestational Age Neonates among Prepregnancy Underweight Women: A Case-Controlled Study

The aim of our study was to investigate whether prepregnancy underweight body mass index (BMI) is associated with preterm birth (PTB) and small-for-gestational age (SGA). This retrospective case-control study included 814 women with live singleton fetuses in vertex presentation that gave birth between January 2016 and November 2016 in two tertiary care hospitals. The study group (n = 407) comprised all women whose prepregnancy BMI was underweight (<18.5 kg/m²) and who delivered during the study period. A control group (n = 407) was established with women whose prepregnancy BMI was normal (18.5–24.9 kg/m²) by matching age and parity. Univariate and multivariate analyses were performed to compare PTB and SGA associated with prepregnancy underweight BMI. Compared with the control group, the study group had higher rates of overall PTB (10.1% vs. 5.7%, p = 0.02), iatrogenic PTB (4.2% vs. 1.5%, p = 0.02), and SGA (22.1% vs. 11.1%, p < 0.001). In a multivariable analysis, prepregnancy underweight BMI was associated with PTB (aOR 2.32, 95% CI 1.12–4.81) and with SGA (aOR 2.38, 95% CI 1.58–3.58). In singleton pregnancies, women’s prepregnancy underweight compared with normal BMI was associated with an increase in PTB and in SGA neonates. Identifying this specific high-risk group is pragmatic and practical for all physicians, and they should be aware about perinatal outcome among underweight women.

Extremely and Very Preterm Deliveries in a Maternity Unit of Inappropriate Level: Analysis of Socio-Residential Factors

PURPOSE

To analyze the socio-residential factors associated with extremely and very preterm deliveries occurring in non-level 3 maternity units in France.

MATERIALS AND METHODS

This is a population-based observational retrospective study using national hospital data from 2012 to 2014. A generalized estimating equations regression model was used to study the characteristics of women who delivered very preterm and the socio-residential risk factors for not delivering in a level 3 maternity unit at 24-31+6d weeks of gestation.

RESULTS

Among deliveries resulting in live births and without contraindication to in-utero transfer, we identified 9198 extremely or very preterm deliveries; 2122 (23.1%) of these were managed in a non-level 3 unit. Our study showed that young maternal age (women under 20 years at delivery) was associated with the risk of giving birth prematurely in a non-level 3 maternity, and particularly in a level 1 maternity unit (adjusted relative risk, 1.53; 95% CI 1.09-2.16). Living more than 30 minutes away from the closest level 3 unit increased the risk of delivering very preterm in a level 1 or 2 unit. Living in an urban area or urban periphery increased the risk of giving birth in a level 2 maternity unit (adjusted relative risk, 1.53; 95% CI 1.28-1.83 and 1.42; 95% CI 1.17-1.71, respectively).

CONCLUSION

This study shows that young pregnant women living more than 30 minutes from a level 3 hospital have an increased risk of delivering in a maternity unit that is not equipped to deal with premature births. The risk also increases with an urban place of residence when the delivery occurs in a level 2 unit. A clearer understanding of the population at risk of delivering prematurely in a non-level 3 maternity could lead to improvements in structuring healthcare to encourage earlier management and better support.

Risk of labor dystocia increases with maternal age irrespective of parity: a population-based register study

INTRODUCTION

Advanced maternal age is associated with labor dystocia (LD) in nulliparous women. This study investigates the age-related risk of LD in first, second and third births.

MATERIAL AND METHODS

All live singleton cephalic births at term (≥ 37 gestational weeks) recorded in the Swedish Medical Birth Register from 1999 to 2011, except elective cesarean sections and fourth births and more, in total 998 675 pregnancies, were included in the study. LD was defined by International Classification of Diseases, version 10 codes (O620, O621, O622, O629, O630, O631 and O639). In each parity group risks of LD at age 25-29 years, 30-34 years, 35-39 years and ≥ 40 years compared with age < 25 years were investigated by logistic regression analyses. Analyses were adjusted for year of delivery, education, country/region of birth, smoking in early pregnancy, maternal height, body mass index, week of gestation, fetal presentation and infant birthweight.

RESULTS

Rates of LD were 22.5%, 6.1% and 4% in first, second and third births, respectively. Adjusted odd ratios (OR) for LD increased progressively from the youngest to the oldest age group, irrespective of parity. At age 35-39 years the adjusted OR (95% CI) was approximately doubled compared with age 25 and younger: 2.13 (2.06-2.20) in first birth; 2.05 (1.91-2.19) in second births; and 1.81 (1.49-2.21) in third births.

CONCLUSIONS

Maternal age is an independent risk factor for LD in first, second and third births. Although age-related risks by parity are relatively similar, more nulliparous than parous women will be exposed to LD due to the higher rate.

[Epidemiology and risk factors of preterm birth]

OBJECTIVE

To synthesize the available evidence regarding the incidence and several risk factors of preterm birth. To describe neonatal outcomes according to gestational age and to the context of delivery.

MATERIALS AND METHODS

Consultation of the Medline database.

RESULTS

In 2010, 11% of live births (15 million babies) occurred before 37 completed weeks of gestation worldwide. About 85% of these births were moderate to late preterm babies (32-36 weeks), 10% were very preterm babies (28-31 weeks) and 5% were extremely preterm babies (<28 weeks). In France, premature birth concerns 60,000 neonates every year, 12,000 of whom are born before 32 completed weeks of gestation. Half of them are delivered after spontaneous onset of labor or preterm premature rupture of the membranes, and the other half are provider-initiated preterm births. Several maternal factors are associated with preterm birth, including sociodemographic, obstetrical, psychological, and genetic factors; paternal and environmental factors are also involved. Gestational age is highly associated with neonatal mortality and with short- and long-term morbidities. Pregnancy complications and the context of delivery also have an impact on neonatal outcomes.

CONCLUSION

Preterm birth is one of the leading cause of the under-five mortality and of neurodevelopmental impairment worldwide; it remains a major public health issue.

Advanced maternal age increases the risk of very preterm birth, irrespective of parity: a population-based register study

OBJECTIVE

To investigate whether advanced maternal age is associated with preterm birth, irrespective of parity.

DESIGN

Population-based registry study.

SETTING

Swedish Medical Birth Register.

POPULATION

First, second, and third live singleton births to women aged 20 years or older in Sweden, from 1990 to 2011 (n = 2 009 068).

METHODS

Logistic regression analysis was used in each parity group to estimate risks of very and moderately preterm births to women at 20-24, 25-29, 30-34, 35-39, and 40 years or older, using 25-29 years as the reference group. Odds ratios (ORs) were adjusted for year of birth, education, country of birth, smoking, body mass index, and history of preterm birth. Age-related risks of spontaneous and medically indicated preterm births were also investigated.

MAIN OUTCOME MEASURES

Very preterm (22-31 weeks of gestation) and moderately preterm (32-36 weeks) births.

RESULTS

Risks of very preterm birth increased with maternal age, irrespective of parity: adjusted ORs in first, second, and third births ranged from 1.18 to 1.28 at 30-34 years, from 1.59 to 1.70 at 35-39 years, and from 1.97 to 2.40 at ≥40 years. In moderately preterm births, age-related associations were weaker, but were statistically significant from 35-39 years in all parity groups. Advanced maternal age increased the risks of both spontaneous and medically indicated preterm births.

CONCLUSIONS

Advanced maternal age is associated with an increased risk of preterm birth, irrespective of parity, especially very preterm birth. Women aged 35 years and older, expecting their first, second, or third births, should be regarded as a risk group for very preterm birth.

TWEETABLE ABSTRACT

Women aged 35 years and older should be regarded as a risk group for very preterm birth, irrespective of parity.

Intergenerational Cohort Study of Preterm and Small-for-Gestational-Age Birth in Twins and Singletons

To date, several studies have investigated the intergenerational effect of preterm and small-for-gestational-age (SGA) births. However, most studies excluded both twin mothers and twin offspring from the analyses. Thus, the objective of this study was to investigate the intergenerational effect of preterm birth and SGA births among twins and singletons. A prospective population-based register study of mother-firstborn offspring pairs recorded in the Swedish Medical Birth Register was performed. The study included 4,073 twins and 264,794 singletons born from 1973-1983 and their firstborns born from 1986-2009. Preterm birth was defined as birth at <37 weeks of gestation, and SGA as birth weight <2 standard deviations of the Swedish standard. Logistic regressions were performed to estimate the intergenerational effect of each birth characteristic. Adjustments were made for maternal grandmothers' and mothers' socio-demographic factors, in addition to maternal birth characteristics. Among mothers born as singletons, being born preterm was associated with an increased risk of delivering a preterm child (adjusted odds ratio (OR) 1.39, 95% Confidence Interval (CI) = 1.29-1.50), while being born SGA increased the likelihood of having an SGA child (adjusted OR 3.04, 95% CI = 2.80-3.30) as well as a preterm child (adjusted OR 1.30, 95% CI = 1.20-1.40). In twin mothers, the corresponding ORs tended to be lower, and the only statistically significant association was between an SGA mother and an SGA child (adjusted OR 2.15, 95% CI = 1.40-3.31). A statistically significant interaction between twinning and mother's size for gestational age was identified in a multivariate linear regression analysis, indicating that singleton mothers born SGA were associated with a lower birth weight compared with mothers not born SGA. Preterm birth and SGA appear to be transferred from one generation to the next, although not always reaching statistical significance. These effects seem to be less evident in mothers born as twins compared with those born as singletons.

Social context of preterm delivery in France in 2011 and impact on short-term health outcomes: the EPIPAGE 2 cohort study

BACKGROUND

Low socio-economic context increases the risk of preterm delivery and may affect short-term outcomes in children born preterm. We described the social context of preterm delivery in France in 2011 and compared it with the general population of deliveries over the same period. We also studied how social context influenced pregnancy and delivery characteristics in the preterm population, and how it affected mortality and short-term morbidity in liveborn preterm children (<35 weeks).

METHODS

We created an individual socio-economic vulnerability index, derived from multiple correspondence analysis based on maternal social information in the French National Perinatal Survey (NPS-2010). Weighted coordinates were applied to families from the EPIPAGE 2 study, a population-based cohort of preterm infants born in 2011, to quantify the infant's exposure to socio-economic vulnerability. Multivariable logistic models were used to relate the socio-economic context to pregnancy and delivery characteristics, and to assess its impact on short-term outcomes of the infants.

RESULTS

Among mothers of preterm infants, gestational age decreased as socio-economic conditions worsened. In the most deprived group, women had more irregular pregnancy care, a higher prevalence of infection during pregnancy, and a lower rate of antenatal corticosteroid administration. The most deprived group was associated with a higher risk of severe morbidity for the preterm neonates.

CONCLUSION

Our results emphasise the need for a large population-based surveillance system to identify the most deprived mothers, and to propose appropriate follow-up and care to these women and their infants in order to enhance long-term health.

Can preterm labour be predicted in low risk pregnancies? Role of clinical, sonographic, and biochemical markers

Background and Objectives. This is a prospective nested cohort study conducted over a period of 3 years. 2644 women were recruited, out of which final analysis was done for 1884 women. Methods. Cervicovaginal and blood samples were collected for all recruited women. Out of these, 137 women who delivered before 35 weeks were treated as cases and equal number of matched controls were chosen. Analysis of samples for serum G-CSF, AFP, ferritin, and cervicovaginal interleukin-6 and IGFBP-1 was done. Results. Poor orodental hygiene, which can be a social marker, was significantly more common in women who delivered preterm (P = 0.008). Serum alkaline phosphatase and serum ferritin were found to be significantly associated with preterm deliveries. The 90th percentile value of these parameters was considered as cut-off as there is no specific cut-off. Conclusions. Our study did not prove usefulness of any predictive marker. Serum ferritin and alkaline phosphatase were found to have correlation but their values are affected in many conditions and need to be elucidated with caution. Larger studies are needed for predicting preterm labour in asymptomatic women.

Passive smoking and preterm birth in urban China

Studies investigating the relationship between maternal passive smoking and the risk of preterm birth have reached inconsistent conclusions. A birth cohort study that included 10,095 nonsmoking women who delivered a singleton live birth was carried out in Lanzhou, China, between 2010 and 2012. Exposure to passive smoking during pregnancy was associated with an increased risk of very preterm birth (<32 completed weeks of gestation; odds ratio = 1.98, 95% confidence interval: 1.41, 2.76) but not moderate preterm birth (32-36 completed weeks of gestation; odds ratio = 0.98, 95% confidence interval: 0.81, 1.19). Risk of very preterm birth increased with the duration of exposure (P for trend = 0.0014). There was no variability in exposures by trimester. The associations were consistent for both medically indicated and spontaneous preterm births. Overall, our findings support a positive association between passive smoking and the risk of very preterm birth.

Gestational age-dependent risk factors for preterm birth: associations with maternal education and age early in gestation

OBJECTIVES

Preterm birth (PTB) before 37 weeks can occur over a wide range of gestational ages, but few studies have assessed if associations between risk factors and PTB vary over the duration of gestation. We sought to evaluate if associations between two major risk factors (maternal education and age) and PTB depend on gestational age at delivery.

STUDY DESIGN

We estimated hazard ratios of PTB for education and age in a time-to-event analysis using a retrospective cohort of 223,756 live singleton births from the province of Québec, Canada for the years 2001-2005. Differences in hazards of maternal education and age with PTB were assessed over gestational age in a Cox proportional hazards model using linear and nonlinear time interaction terms, adjusting for maternal characteristics.

RESULTS

Associations of PTB with lower (vs. higher) education and older (vs. younger) age strengthened progressively at earlier gestational ages, such that the risk of PTB for maternal education and age was not constant over the course of gestation.

CONCLUSIONS

Associations of PTB with risk factors such as maternal low education and older age may be stronger early in gestation. Models that capture the time-dependent nature of PTB may be useful when the goal is to assess associations at low gestational ages, and to avoid masked or biased associations early in gestation.

Psychosocial stress in pregnancy and preterm birth: associations and mechanisms

AIMS

Psychosocial stress during pregnancy (PSP) is a risk factor of growing interest in the etiology of preterm birth (PTB). This literature review assesses the published evidence concerning the association between PSP and PTB, highlighting established and hypothesized physiological pathways mediating this association.

METHOD

The PubMed and Web of Science databases were searched using the keywords "psychosocial stress", "pregnancy", "pregnancy stress", "preterm", "preterm birth", "gestational age", "anxiety", and "social support". After applying the exclusion criteria, the search produced 107 articles.

RESULTS

The association of PSP with PTB varied according to the dimensions and timing of PSP. Stronger associations were generally found in early pregnancy, and most studies demonstrating positive results found moderate effect sizes, with risk ratios between 1.2 and 2.1. Subjective perception of stress and pregnancy-related anxiety appeared to be the stress measures most closely associated with PTB. Potential physiological pathways identified included behavioral, infectious, neuroinflammatory, and neuroendocrine mechanisms.

CONCLUSIONS

Future research should examine the biological pathways of these different psychosocial stress dimensions and at multiple time points across pregnancy. Culture-independent characterization of the vaginal microbiome and noninvasive monitoring of cholinergic activity represent two exciting frontiers in this research.

The social determinants of infant mortality and birth outcomes in Western developed nations: a cross-country systematic review

Infant mortality (IM) and birth outcomes, key population health indicators, have lifelong implications for individuals, and are unequally distributed globally. Even among western industrialized nations, striking cross-country and within-country patterns are evident. We sought to better understand these variations across and within the United States of America (USA) and Western Europe (WE), by conceptualizing a social determinants of IM/birth outcomes framework, and systematically reviewing the empirical literature on hypothesized social determinants (e.g., social policies, neighbourhood deprivation, individual socioeconomic status (SES)) and intermediary determinants (e.g., health behaviours). To date, the evidence suggests that income inequality and social policies (e.g., maternal leave policies) may help to explain cross-country variations in IM/birth outcomes. Within countries, the evidence also supports neighbourhood SES (USA, WE) and income inequality (USA) as social determinants. By contrast, within-country social cohesion/social capital has been underexplored. At the individual level, mixed associations have been found between individual SES, race/ethnicity, and selected intermediary factors (e.g., psychosocial factors) with IM/birth outcomes. Meanwhile, this review identifies several methodological gaps, including the underuse of prospective designs and the presence of residual confounding in a number of studies. Ultimately, addressing such gaps including through novel approaches to strengthen causal inference and implementing both health and non-health policies may reduce inequities in IM/birth outcomes across the western developed world.

Neighbourhood deprivation and very preterm birth in an English and French cohort

BACKGROUND

Social factors affect the risk of very preterm birth and may affect subsequent outcomes in those born preterm. We assessed the influence of neighbourhood socio-economic characteristics on the risk and outcomes of singleton very preterm birth (<32 weeks of gestation) in two European regions with different health systems.

METHODS

Live births (n=1118) from a population-based cohort of very preterm infants in 2003 in Trent (UK) and Ile-de-France (France) regions were geocoded to their neighbourhood census tracts. Odds ratios for very preterm singleton birth by neighbourhood characteristics (unemployment rate, proportion manual workers, proportion with high school education only, non home ownership) were computed using infants enumerated in the census as a control population. The impact of neighbourhood variables was further assessed by pregnancy and delivery characteristics and short term infant outcomes.

RESULTS

Risk of very preterm singleton birth was higher in more deprived neighbourhoods in both regions (OR between 2.5 and 1.5 in the most versus least deprived quartiles). No consistent associations were found between neighbourhood deprivation and maternal characteristics or health outcomes for very preterm births, although infants in more deprived neighbourhoods were less likely to be breastfed at discharge.

CONCLUSIONS

Neighbourhood deprivation had a strong consistent impact on the risk of singleton very preterm birth in two European regions, but did not appear to be associated with maternal characteristics or infant outcomes. Differences in breastfeeding at discharge suggest that socio-economic factors may affect long term outcomes.

Public Health Impact of Legal Termination of Pregnancy in the US: 40 Years Later

During the 40 years since the US Supreme Court decision in Doe versus Wade and Doe versus Bolton, restrictions on termination of pregnancy (TOP) were overturned nationwide. The use of TOP was much wider than predicted and a substantial fraction of reproductive age women in the U.S. have had one or more TOPs and that widespread uptake makes the downstream impact of any possible harms have broad public health implications. While short-term harms do not appear to be excessive, from a public perspective longer term harm is conceiving, and clearly more study of particular relevance concerns the associations of TOP with subsequent preterm birth and mental health problems. Clearly more research is needed to quantify the magnitude of risk and accurately inform women with the crisis of unintended pregnancy considering TOP. The current US data-gathering mechanisms are inadequate for this important task.

Very low and low birth weight associated with maternal periodontitis

AIM

The aim of this study was to evaluate the association of very low and low birth weight (VLBW and LBW) with maternal periodontitis.

MATERIAL AND METHODS

Overall, 1206 women were examined at post-partum and two alternative criteria for periodontitis definition were used: (1) four or more teeth with at least one site with probing depth (PD) ≥ 4 mm and clinical attachment loss (CAL) ≥ 3 mm; and (2) at least one site with PD and CAL ≥ 4 mm. For each definition, two multivariate analyses were performed: (1) linear regression for birth weight; (2) ordinal logistic regression for birth weight, categorized as adequate (n = 1046), LBW (n = 145) and VLBW (n = 15).

RESULTS

Linear regression showed that maternal periodontitis was associated with a decrease in mean birth weight (periodontitis definition 1: p = 0.027; periodontitis definition 2: p = 0.003). Ordinal logistic regression showed that maternal periodontitis was associated with LBW and VLBW [odds ratio (OR) = 2.0; 95% confidence interval (CI) 1.39-2.90, when considering periodontitis definition 2]; and with LBW (OR = 1.65; 95% CI 1.15-2.36, when considering periodontitis definition 1).

CONCLUSION

Maternal periodontitis was associated with a decrease in mean birth weight, as well as with LBW and VLBW.

The preterm birth syndrome: issues to consider in creating a classification system

A comprehensive classification system for preterm birth requires expanded gestational boundaries that recognize the early origins of preterm parturition and emphasize fetal maturity over fetal age. Exclusion of stillbirths, pregnancy terminations, and multifetal gestations prevents comprehensive consideration of the potential causes and presentations of preterm birth. Any step in parturition (cervical softening and ripening, decidual-membrane activation, and/or myometrial contractions) may initiate preterm parturition, and should be recorded for every preterm birth, as should the condition of the mother, fetus, newborn, and placenta, before a phenotype is assigned.

Ethnic disparity in spontaneous preterm birth and maternal pre-pregnancy body mass index

PURPOSE

To investigate differences in pre-pregnancy BMI status in patients with spontaneous preterm birth (PTB) compared with term birth and assess the role of ethnicity as a risk modifier in BMI-associated PTB.

METHODS

A case-control study involving self-reported African American and Caucasian women delivering singletons in Nashville, TN, USA, 2003-2009. Maternal pre-pregnancy BMI was recorded in 447 PTB-cases (African American = 145, Caucasian = 302) and 1315 term-birth controls (African American = 522; Caucasian = 793). Crude and adjusted odds ratio (OR and AOR) for PTB were calculated using normal BMI (18.5-24.9 kg/m(2)) as reference. Age, education, marital status, income, smoking, parity, previous PTB and pregnancy weight gain were included as covariates in logistic regression.

RESULTS

No significant differences were noted in the OR for PTB among different BMI categories when women of different ethnicity were combined. Odds of PTB were greater in obese than in normal weight Caucasian women, even after adjusting for confounders (AOR = 1.84, 95%CI [1.15, 2.95]). Obese African American women had a decreased crude OR for PTB, although this was not significant after adjusting for confounders (AOR = 0.72, 95%CI [0.38, 1.40]). The odds for early PTB (<32 weeks) were decreased in obese compared with normal weight African American women (OR = 0.23, 95%CI [0.08, 0.70]), whereas they were increased in obese compared with normal weight Caucasian women (OR = 2.30, 95%CI [1.32, 4.00]).

CONCLUSION

The risk for PTB in women with different pre-pregnancy BMI categories differs according to ethnicity.

Maternal underweight and the risk of preterm birth and low birth weight: a systematic review and meta-analyses

BACKGROUND

Despite the current obesity epidemic, maternal underweight remains a common occurrence with potential adverse perinatal outcomes. Our objective was to determine the relationship between maternal underweight and preterm birth (PTB) and low birth weight (LBW) in singleton pregnancies in developing and developed countries.

METHODS

We followed the MOOSE consensus statement. We searched MEDLINE and EMBASE from their inceptions. We included studies that assessed the effect of maternal underweight compared with normal weight according to body mass index in singleton gestations on our two primary outcomes: PTB (<37 weeks) and LBW (<2500 g). Two assessors independently reviewed citations, extracted data and assessed quality.

RESULTS

A total of 78 studies were included involving 1 025 794 women. The overall risk of PTB was increased in the cohort studies of underweight women [adjusted relative risk (RR) 1.29, 95% confidence interval (CI) 1.15-1.46], as were the risks of spontaneous PTB (adjusted RR 1.32, 95% CI 1.10-1.57) and induced PTB (adjusted RR 1.21, 95% CI 1.07-1.36). Underweight women had an increased risk of an LBW infant (adjusted RR 1.64, 95% CI 1.38-1.94). In developed countries, underweight women had an increased risk of PTB (RR 1.22, 95% CI 1.15-1.30) but not in developing countries (RR 0.99, 95% CI 0.67-1.45). In both developed and developing countries, underweight women were at increased risk of having an LBW infant (RR 1.48, 95% CI 1.29-1.68, and RR 1.52, 95% CI 1.25-1.85, respectively).

CONCLUSIONS

In this systematic review and meta-analyses, we determined that singletons born to underweight women have higher risks of PTB (overall, spontaneous and induced) and LBW than those born to women with normal weight.

Modelling prior reproductive history to improve prediction of risk for very preterm birth

In published studies of preterm birth, analyses have usually been centred on individual reproductive events and do not account for the joint distributions of these events. In particular, spontaneous and induced abortions have often been studied separately and have been variously reported as having no increased risk, increased risk or different risks for subsequent preterm birth. In order to address this inconsistency, we categorised women into mutually exclusive groups according to their reproductive history, and explored the range of risks associated with different reproductive histories and assessed similarities of risks between different pregnancy histories. The data were from a population-based case-control study, conducted in Victoria, Australia. The study recruited women giving birth between April 2002 and April 2004 from 73 maternity hospitals. Detailed reproductive histories were collected by interview a few weeks after the birth. The cases were 603 women who had had a singleton birth between 20 and less than 32 weeks gestation (very preterm births including terminations of pregnancy) and the controls were 796 randomly selected women from the population who had had a singleton birth of at least 37 completed weeks gestation. All birth outcomes were included. Unconditional logistic regression was used to assess the association of very preterm birth with type and number of prior abortions, prior preterm births and sociodemographic factors. Using the complex combinations of prior pregnancy experiences of women (including nulligravidity), we showed that a history of prior childbirth (at term) with no preterm births gave the lowest risk of very preterm birth. With this group as the reference category, odds ratios of more than two were associated with all other prior reproductive histories. There was no evidence of difference in risk between types of abortion (i.e. spontaneous or induced) although the risk increased if a prior preterm birth had also occurred. There was an increasing risk of very preterm birth associated with increasing numbers of abortions. This method of data analysis reveals consistent and similar risks for very preterm birth following spontaneous or induced abortions. The findings point to the need to explore commonalities rather than differences in regard to the impact of abortion on subsequent births.

Effect of psychosocial stress and physical activity on preterm birth: a cohort study

AIM

To determine trimester-specific effects of risk factors for preterm birth (PTB).

METHODS

A prospective study was carried out in a district of Sri Lanka. A total of 885 pregnant mothers were recruited at equal to or less than 16 weeks of gestation and followed up until partus. Trimester-specific exposure statuses and potential confounding factors were gathered on average at the 12th, 28th, and 36th weeks of gestation. Physical activities were assessed by obtaining information about the duration of specific postures adopted per day by housewives during each trimester at home and both at home and during working hours for those who were engaged in paid employment. Psychosocial stress was assessed using the Modified Life Events Inventory and the General Health Questionnaire 30. Multiple logistic regression analysis was applied and the results were expressed as adjusted odds ratios (OR) and 95% confidence intervals (95%CI).

RESULTS

Standing equal to or less than 2.5 h/day during the first or second or both trimesters (OR 1.83, 95%CI 1.03, 3.25), maternal age of <25 years (OR 1.73, 95%CI 1.02, 2.95), education up to primary school level (OR 3.30, 95%CI 1.3, 8.36) and past history of low birthweight (OR 2.52, 95%CI 1.16, 5.48) were risk factors for PTB. Psychosocial stress was not found to be a risk factor for PTB.

CONCLUSIONS

Standing equal to or less than 2.5 h/day during the early trimesters was a risk factor for PTB among uncomplicated pregnancies. Further studies are recommended to assess the trimester-specific effect of psychosocial stress on PTB.

Overweight and obesity in mothers and risk of preterm birth and low birth weight infants: systematic review and meta-analyses

OBJECTIVE

To determine the relation between overweight and obesity in mothers and preterm birth and low birth weight in singleton pregnancies in developed and developing countries.

DESIGN

Systematic review and meta-analyses.

DATA SOURCES

Medline and Embase from their inceptions, and reference lists of identified articles.

STUDY SELECTION

Studies including a reference group of women with normal body mass index that assessed the effect of overweight and obesity on two primary outcomes: preterm birth (before 37 weeks) and low birth weight (<2500 g).

DATA EXTRACTION

Two assessors independently reviewed titles, abstracts, and full articles, extracted data using a piloted data collection form, and assessed quality.

DATA SYNTHESIS

84 studies (64 cohort and 20 case-control) were included, totalling 1 095 834 women. Although the overall risk of preterm birth was similar in overweight and obese women and women of normal weight, the risk of induced preterm birth was increased in overweight and obese women (relative risk 1.30, 95% confidence interval 1.23 to 1.37). Although overall the risk of having an infant of low birth weight was decreased in overweight and obese women (0.84, 0.75 to 0.95), the decrease was greater in developing countries than in developed countries (0.58, 0.47 to 0.71 v 0.90, 0.79 to 1.01). After accounting for publication bias, the apparent protective effect of overweight and obesity on low birth weight disappeared with the addition of imputed "missing" studies (0.95, 0.85 to 1.07), whereas the risk of preterm birth appeared significantly higher in overweight and obese women (1.24, 1.13 to 1.37).

CONCLUSIONS

Overweight and obese women have increased risks of preterm birth and induced preterm birth and, after accounting for publication bias, appeared to have increased risks of preterm birth overall. The beneficial effects of maternal overweight and obesity on low birth weight were greater in developing countries and disappeared after accounting for publication bias.

A case-control study of preterm delivery risk factors according to clinical subtypes and severity

AIMS

To examine risk factors of preterm delivery (PTD) among Thai women.

METHODS

Our case-control study included 467 term controls and 467 PTD cases. PTD was studied in aggregate and in subgroups (i.e. spontaneous preterm labor and delivery [SPTD], preterm premature rupture of membrane [PPROM], medically indicated preterm delivery [MIPTD], moderate preterm delivery [32-36 weeks], and very preterm delivery [<32 weeks]). We used multivariable logistic regression procedures to estimate odds ratio (OR) and 95% confidence intervals (CI) of potential PTD risk factors.

RESULTS

Advanced maternal age (>or=35 years) was associated with a 2.27-fold increased PTD risk overall (95%CI: 1.40, 3.68); and with a 3.79-fold increased risk of MIPTD (95%CI: 1.89, 7.59). Young maternal age (<20 years) was associated with a 2.07-fold increased risk of SPTD (95%CI: 1.19, 3.61). Prior history of PTD was associated with a 3.64-fold increased PTD risk overall (95%CI: 1.87, 7.09), and with a 5.69-fold increased risk of MIPTD (95%CI: 2.44, 13.24). No prenatal care was associated with all PTD subtypes. Lean women (body mass index < 18.5 kg/m(2)), compared with normal weight women (18.5-24.9 kg/m(2)), had a 1.70-fold increased risk of PTD (95%CI: 1.21, 2.39). Risk of SPTD (OR = 2.16, 95%CI: 1.44, 3.24) and very PTD (OR = 2.45, 95%CI: 1.35, 4.45) were also elevated in lean women.

CONCLUSIONS

Maternal age, pre-pregnancy body mass index, prior history of PTD and no utilization of prenatal care were covariates identified in this study as risk factors for PTD. Our findings also suggest heterogeneity in risk factors for clinical subtypes of PTD.

Maternal periodontal disease and preterm or extreme preterm birth: an ordinal logistic regression analysis

BACKGROUND

Despite previous studies addressing the link between preterm or low birth weight infants and maternal periodontitis, extreme preterm births have received far less attention. This study is designed to address the possible association between maternal periodontal disease and preterm or extreme preterm birth.

METHODS

Immediately after childbirth, 1,207 women underwent an examination in which periodontal disease was assessed according to two alternative definitions: 1) four or more teeth with at least one site showing probing depth (PD) >or=4 mm and clinical attachment loss (AL) >or=3 mm, and 2) at least one site showing PD and clinical AL >or=4 mm. For each of these definitions, two types of multivariate analysis were conducted: a linear regression analysis for the number of gestation weeks, and a more specific ordinal logistic regression analysis for the ordinal variable gestation time categorized as normal (term) (n = 1,046 women) or mild-moderate (n = 146 women) or extreme preterm (n = 15 women).

RESULTS

Periodontal disease was associated with fewer weeks of gestation by linear regression (definition 1: P = 0.012; definition 2: P <0.001) and with preterm (n = 161; mild-moderate and extreme) or extreme preterm births (n = 15) by ordinal logistic regression (definition 1: odds ratio [OR] = 1.83, 95% confidence interval [CI]: 1.28 to 2.62; definition 2: OR = 2.37, 95% CI: 1.62 to 3.46).

CONCLUSION

Our findings suggest that periodontal disease is associated with a premature or extremely premature birth.

Trends in preterm births in Flanders, Belgium, from 1991 to 2002

Changes in the preterm birth rate have been attributed predominantly to increases in multiple pregnancies, associated with advanced maternal age and assisted reproduction, and to obstetric intervention. We examined their contribution to the frequencies of preterm (<37 weeks), very preterm (<32 weeks) and severely preterm (<28 weeks) birth among 700 383 singleton and twin births in Flanders from 1991 to 2002. We examined changes across four 3-year periods (triennia) with confidence interval [CI] analysis and yearly incremental rates using linear and logistic regression analyses. Over the 12 years, twin pregnancies increased from 1.5% to 2.0%, averaging 1.6% [95% CI 1.54, 1.66] in 1991-93 and 1.9% [95% CI 1.81, 1.94] in 2000-02 (P < 0.001). The proportion of women aged 35 years or more increased from 6.8% [95% CI 6.69, 6.92] in 1991-93 to 11.3% [95% CI 11.2, 11.5] in 2000-02 (P < 0.001) and those aged under 20 from 1.9% [95% CI 1.81, 1.93] to 2.3% [95% CI 2.26, 2.41] (P < 0.001). Assisted reproduction increased from 2.6% [95% CI 2.48, 2.62] to 4.2% [95% CI 4.11, 4.30] (P < 0.001) and obstetric intervention to end pregnancy from 36.2% [95% CI 36.0, 36.4] to 40.3% [95% CI 40.1, 40.6] (P < 0.001). These increases related to an annual increase of 0.23% in the preterm birth rate from 5.5% [95% CI 5.4, 5.6] in 1991-93 to 7.2% [95% CI 7.1, 7.3] in 2000-02 (P < 0.001). The proportions of very and severely preterm births also increased by nearly a third, but their contribution to the total preterm birth rate remained stable at 15% and 5%, respectively. Odds ratios for the increases per year were 1.035 [95% CI 1.032, 1.038] for preterm birth, 1.024 [95% CI 1.018, 1.031] for very preterm and 1.028 [95% CI 1.017, 1.040] for severely preterm births after adjusting for other changes in the population. Overall, the data show, first, marked increases in the frequency of known contributors to the preterm birth rate, including twin pregnancies, advanced maternal age, assisted reproduction and obstetric intervention. Second, the preterm birth rate further increased significantly within subgroups of women with one or more of these characteristics. Third, the preterm birth rate also rose, from 4.4% [95% CI 4.2, 4.5] in 1991-93 to 5.6% [95% CI 5.5, 5.8] in 2000-02 (P < 0.001), in women with none of these contributing factors. This indicates that changes in the frequency of these known predictors are insufficient to explain the steady increase in preterm, very preterm and severely preterm births over more than a decade.

Late pre-term (32 – 36 weeks) birth in a North London hospital

Most of the complications of pre-term delivery arise in the 1 - 2% of births before 32 weeks' gestation. However, late pre-term birth (32 - 36 weeks' gestation) is still worrying for the mother and clinician. In a retrospective study that compared the management and outcome of 103 singleton pregnancies delivered between 32 and 36 weeks' of gestation with 103 age-matched controls that delivered at term, a short inter-pregnancy interval, early pregnancy bleeding, pre-labour spontaneous rupture of membranes, a history of pre-term delivery and Asian race or single marital status were found to be significant factors. The groups did not differ in parity, BMI, smoking status or history of miscarriages and terminations. Following a logistic regression analysis, the following emerged as risk factors for late pre-term delivery; a history of previous pre-term delivery (OR = 7.2; 95% CI 1.6 - 33.2), a short (<12 months) inter-pregnancy interval (OR = 4.1; 95% CI 2.2 - 7.5), early pregnancy bleeding (OR = 7.6; 95% CI 1.3 - 38.3) and pre-labour spontaneous rupture of membranes (OR = 13.3, 95% CI 3.1 - 55.2).

Demographic, clinical and occupational characteristics associated with early onset of delivery: findings from the Duke Health and Safety Surveillance System, 2001-2004

BACKGROUND

This cross-sectional study explores associations between preterm delivery and demographic, clinical and occupational characteristics of women employed within a university and health system.

METHODS

A comprehensive surveillance system linking individual-level data from Human Resources, medical insurance claims and a job-exposure matrix was used to identify women with a single live birth between 2001 and 2004 and describe maternal characteristics during pregnancy.

RESULTS

Preterm delivery occurred in 7.1% (n = 74) of the 1,040 women, a lower preterm delivery prevalence than observed in the general U.S. population. Nearly all (>99.5%) women utilized prenatal care services. Prevalence of preterm delivery was highest for inpatient nurses, nurses' aides and office staff. In multivariate analyses, preterm delivery was positively associated with several clinical conditions: placenta previa, diabetes and cardiovascular disorder/disease.

CONCLUSIONS

We observed associations between preterm delivery and several previously indicated clinical conditions. Further study of the effect of job characteristics on preterm delivery is warranted.

Invited commentary: disaggregating preterm birth to determine etiology

Identifying the causes of preterm birth has been problematic, in part because of heterogeneous pathways leading to the same event, early delivery. If a risk factor affects only a subset of cases, then studies that address the aggregate outcome will generate diluted measures of association. McElrath et al. (Am J Epidemiol. 2008;168(9):980-989) examined an array of potential influences on very early preterm birth (<28 weeks' gestation) and divided cases on the basis of proximal causes. Through factor analysis, they found empirical support for dividing preterm cases into 2 groups: intrauterine inflammation (preterm labor, preterm membrane rupture, placental abruption, and cervical insufficiency) and abnormal placentation (preeclampsia and intrauterine growth restriction). Replication of this classification in less extreme preterm births is needed, requiring large numbers of preterm births that have been characterized in detail. Nonetheless, this division is worthy of study by using previously collected data to determine whether, in fact, stronger associations are found for these subsets than for preterm birth in the aggregate. Ultimately, the test of the approach is in improving our understanding of etiology, ideally generating stronger, more consistent associations with preterm birth subsets than have been found for preterm birth in the aggregate.

Socioeconomic position and the risk of preterm birth--a study within the Danish National Birth Cohort

BACKGROUND

Low socioeconomic position is generally associated with increased risk of preterm birth, but it remains unclear whether the inequality depends on the socioeconomic measure used, if the associations differ according to the degree of prematurity, and how individual level risk factors mediate the association.

METHODS

The hazard ratios (HR) of preterm birth associated with five different measures of socioeconomic position and three degrees of preterm birth were analysed in a dataset of 75 890 singleton pregnancies (1996-2002) from the Danish National Birth Cohort. This, and the mediating role of selected individual level risk factors (smoking, alcohol consumption, binge drinking, pre-pregnancy body mass index, gestational weight gain) were estimated, using Cox regression analyses.

RESULTS

Mothers with <10 years of education had an elevated risk of preterm birth compared with mothers with >12 years of education and the association interacted with parity, while income and occupation affected the risk to a lesser degree. The adjusted HR for less educated nulliparous and parous women were 1.22 (95% CI 1.04-1.42) and 1.56 (95% CI 1.31-1.87), respectively, compared with women with >12 years of education. For parous women with <10 years of education inclusion of smoking in the model decreased the HR of preterm birth to 1.43 (95% CI 1.19-1.72).

CONCLUSIONS

Maternal educational level was the strongest predictor of preterm birth among five socioeconomic measures and the gradient did not differ significantly according to the degree of preterm birth. For parous women smoking explained some of the educational gradient but in general the selected risk factors only reduced the relative educational gradient in preterm birth marginally.

Epidemiology and environmental factors in preterm labour

An epidemiological and environmental approach is the appropriate starting point to understanding preterm labour. Although there are multiple aetiologies it seems likely that anthropometric and environmental risk factors in combination with inherent genetic susceptibilities contribute to an increased risk of preterm labour for certain women. Poct 2pulation-based studies identifying risk factors and quantifying outcomes facilitate informed counselling and provide a framework for developing prediction tools. Carefully conducted case-control and cohort studies identify associations that may contribute to an understanding of causation. A combined approach encompassing epidemiology, pathophysiology and clinical research is required to understand the aetiologies, prevention and optimal management of preterm labour. This review focuses on the epidemiology of preterm labour and the role of environmental factors.

The contribution of preterm birth to the Black-White infant mortality gap, 1990 and 2000

OBJECTIVES

We evaluated whether the decline of the racial disparity in preterm birth during the last decade was commensurate with a decline in the contribution of preterm birth to the infant mortality gap.

METHODS

We used linked files of 1990 and 2000 data on US infant births and deaths to partition the gap between Black and White infant mortality rates into differences in the (1) distribution of gestational age and (2) gestational age-specific mortality rates.

RESULTS

Between 1990 and 2000, the Black-White infant mortality rate ratio did not change significantly (2.3 vs 2.4). Excess deaths among preterm Black infants accounted for nearly 80% of the Black-White infant mortality gap in both 1990 and 2000. The narrowing racial disparity in the preterm birth rate was counterbalanced by greater mortality reductions in White than in Black preterm infants. Extremely preterm birth (<28 weeks) was 4 times higher in Black infants and accounted for more than half of the infant mortality gap.

CONCLUSIONS

Substantial reductions in the Black-White infant mortality gap will require improved prevention of extremely preterm birth among Black infants.

Intergenerational effects of preterm birth and reduced intrauterine growth: a population-based study of Swedish mother-offspring pairs

OBJECTIVE

To estimate the intergenerational effects of preterm birth and reduced intrauterine growth.

DESIGN

Population-based cohort study.

SETTINGS

Mother-first-born offspring pairs recorded in the Swedish Medical Birth Registry.

POPULATION

Children born before 2001 to 38 720 women born in 1973-75.

METHODS

The relationships between the mother's and the child's birth characteristics were estimated using logistic regression analysis. Adjustments were made for smoking habits, body mass index (BMI), and current and childhood socio-economic conditions. Analyses were performed on all mother-offspring pairs and on the pairs for which information on neither of the included background variables was missing (n= 24 520).

MAIN OUTCOME MEASURES

Preterm birth (<37 weeks of gestation) and small for gestational age (SGA) (<-2 SD of the Swedish standard).

RESULTS

Mothers who themselves had been born preterm were not significantly more likely to deliver their own children preterm, compared with those who had been born at term (adjusted OR 1.24, 95% CI 0.95-1.62). Also, preterm birth in the mothers did not influence the occurrence of SGA in the children. However, the odds ratio for giving birth to SGA and preterm children, respectively, was higher among SGA mothers (OR 2.68, 95% CI 2.11-3.41 and OR 1.30, 95% CI 1.05-1.61). Mothers whose intrauterine growth was moderately reduced but who did not meet the criterion of being born SGA were also at higher risk of giving birth to both preterm and SGA children, respectively.

CONCLUSIONS

The present study showed evidence of intergenerational effects of reduced intrauterine growth even when socio-economic factors as well as BMI and smoking were adjusted for. There was, however, no consistent intergenerational effect of preterm birth.

Previous induced abortions and the risk of very preterm delivery: results of the EPIPAGE study

OBJECTIVES

To evaluate the risk of very preterm birth (22-32 weeks of gestation) associated with previous induced abortion according to the complications leading to very preterm delivery in singletons.

DESIGN

Multicentre, case-control study (the French EPIPAGE study).

SETTING

Regionally defined population of births in France.

SAMPLE

The sample consisted of 1943 very preterm live-born singletons (< 33 weeks of gestation), 276 moderate preterm live-born singletons (33-34 weeks) and 618 unmatched full-term controls (39-40 weeks).

METHODS

Data from the EPIPAGE study were analysed using polytomous logistic regression models to control for social and demographic characteristics, lifestyle habits during pregnancy and obstetric history. The main mechanisms of preterm delivery were classified as gestational hypertension, antepartum haemorrhage, fetal growth restriction, premature rupture of membranes, idiopathic preterm labor and other causes.

MAIN OUTCOME MEASURES

Odds ratios for very preterm birth by gestational age and by pregnancy complications leading to preterm delivery associated with a history of induced abortion.

RESULTS

Women with a history of induced abortion were at higher risk of very preterm delivery than those with no such history (OR + 1.5, 95% CI 1.1-2.0); the risk was even higher for extremely preterm deliveries (< 28 weeks). The association between previous induced abortion and very preterm delivery varied according to the main complications leading to very preterm delivery. A history of induced abortion was associated with an increased risk of premature rupture of the membranes, antepartum haemorrhage (not in association with hypertension) and idiopathic spontaneous preterm labour that occur at very small gestational ages (< 28 weeks). Conversely, no association was found between induced abortion and very preterm delivery due to hypertension.

CONCLUSION

Previous induced abortion was associated with an increased risk of very preterm delivery. The strength of the association increased with decreasing gestational age.

Does smoking in pregnancy modify the impact of antenatal steroids on neonatal respiratory distress syndrome? Results of the Epipage study

OBJECTIVES

To assess the relation between cigarette smoking during pregnancy and neonatal respiratory distress syndrome (RDS) in very preterm birth, and to analyse the differential effect of antenatal steroids on RDS among smokers and non-smokers.

DESIGN

A population based cohort study (the French Epipage study).

SETTING

Regionally defined births in France.

METHODS

A total of 858 very preterm liveborn singletons (27-32 completed weeks of gestation) of the French Epipage study were included in this analysis. The odds ratio for RDS in relation to smoking in pregnancy was estimated using a logistic regression to control for gestational age. The odds ratio for RDS in relation to antenatal steroids was estimated taking into account an interaction between antenatal steroids and cigarette smoking, using multiple logistic regression to control for gestational age, birthweight ratio, main causes of preterm birth, mode of delivery, and sex.

RESULTS

The odds ratio for RDS in relation to smoking in pregnancy adjusted for gestational age (aOR) was 0.59 (95% confidence interval (CI) 0.44 to 0.79). The aOR for RDS in relation to antenatal steroids was 0.31 (95% CI 0.19 to 0.49) in babies born to non-smokers and 0.63 (95% CI 0.38 to 1.05) in those born to smokers; the difference was significant (p = 0.04).

CONCLUSIONS

Cigarette smoking during pregnancy is associated with a decrease in the risk of RDS in very preterm babies. Although antenatal steroids reduce the risk of RDS in babies born to both smokers and non-smokers, the reduction is smaller in those born to smokers.

Employment, working conditions, and preterm birth: results from the Europop case-control survey

STUDY OBJECTIVE

To analyse the relation between preterm birth and working conditions in Europe using common measures of exposure and to test whether employment related risks varied by country of residence.

DESIGN

A case-control study in which cases included all consecutive singleton preterm births and controls included one of every ten singleton term births in each participating maternity unit. Data about working conditions were obtained by interview from women after delivery.

SETTING

Sixteen European countries.

PARTICIPANTS

The analysis included 5145 preterm and 7911 term births of which 2369 preterm and 4098 term births were to women employed during pregnancy. Analyses of working conditions were carried out for women working through at least the third month of pregnancy.

MAIN RESULTS

Employed women did not have an excess risk of preterm birth. Among working women, a moderate excess risk was observed for women working more than 42 hours a week (OR = 1.33, CI = 1.1 to 1.6), standing more than six hours a day (OR = 1.26, CI = 1.1 to 1.5), and for women with low job satisfaction (OR = 1.27, CI = 1.1 to 1.5). There were stronger links in countries with a lower overall level of perinatal health and a common practice of long prenatal leaves.

CONCLUSION

These findings show that specific working conditions affect the risk of preterm birth. They also suggest employment related risks could be mediated by the social and legislative context.

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.

Preschool outcome of less than 801-gram preterm infants compared with full-term siblings

OBJECTIVE

Extremely low birth weight (ELBW) infants are at greater risk for neurodevelopmental delay than full-term infants. Outcomes may be compromised secondary to abnormal brain development associated with complications of prematurity. Long-term cognitive outcome has also been reported to be significantly influenced by postnatal factors. The objective of this study was to clarify the effects of prematurity separate from environmental factors on growth and neurodevelopmental outcomes by comparing ELBW children with their full-term siblings.

METHODS

The study consisted of 25 ELBW children, a subset selected from a larger population of infants who were <801 g birth weight and enrolled in a longitudinal follow-up project from birth and their 25 full-term, full-weight siblings. Twenty-three sets of siblings were evaluated at 5 years of age and 2 sets at 3 years of age with standardized medical, social, cognitive, motor, and language testing. Physical and neurodevelopmental outcomes were compared between groups, controlling for gender and socioeconomic status (SES).

RESULTS

At follow-up, ELBW children were lighter, were shorter, and had smaller head circumference. The ELBW children had lower Stanford-Binet IQs (85 +/- 12 [mean +/- SD] and 95 +/- 11), with lower Stanford-Binet subtests except short-term memory and quantitative reasoning, lower spelling scores on the Wide Range Achievement Test, and lower Peabody motor quotients (79 +/- 11 and 92 +/- 17). Preschool Language Scale quotients were not different, but other receptive language measures were lower for ELBW children. High SES seemed to modify the impact of preterm status on cognitive and language but not motor scores. The mean IQ for high-SES ELBW children was equivalent to that of the low-SES term siblings.

CONCLUSIONS

Preschool-age cognitive and language functioning in ELBW children seemed to be affected by both prenatal and birth influences (preterm status) and postnatal influences (SES variables). Motor scores were significantly related to preterm status but not to SES.

The complex relationship between smoking in pregnancy and very preterm delivery. Results of the Epipage study

OBJECTIVE

To assess the relationship between cigarette smoking during pregnancy and very preterm births, according to the main mechanisms of preterm birth.

DESIGN

Case-control study (the French Epipage study).

SETTING

Regionally defined population of births in France.

POPULATION

Eight hundred and sixty-four very preterm live-born singletons (between 27 and 32 completed weeks of gestation) and 567 unmatched full-term controls.

METHODS

Data from the French Epipage study were analysed using a polytomous logistic regression model to control for social and demographic characteristics, pre-pregnancy body mass index and obstetric history. The main mechanisms of preterm delivery were classified as gestational hypertension, antepartum haemorrhage, premature rupture of membranes, spontaneous preterm labour and other miscellaneous mechanisms.

MAIN OUTCOME MEASURES

Odds ratios for very preterm birth for low to moderate (1-9 cigarettes/day) and heavy (>/=10 cigarettes/day) maternal smoking in pregnancy, estimated according to the main mechanisms leading to preterm birth.

RESULTS

Smokers were more likely to give birth to very preterm infants than non-smokers [adjusted odds ratio (aOR) 1.7, 95% confidence interval (CI) 1.3-2.2]. Heavy smoking significantly reduced the risk of very preterm birth due to gestational hypertension (aOR 0.5, 95% CI 0.3-1.0), whereas both low to moderate and heavy smoking increased the risk of very preterm birth due to all other mechanisms (aOR between 1.6 and 2.8).

CONCLUSION

These data from the Epipage study show that maternal smoking during pregnancy is a risk factor for very preterm birth. The impact of maternal smoking on very preterm birth appears to be complex: it lowers the risk of very preterm birth due to gestational hypertension, but increases the risk of very preterm birth due to other mechanisms. These findings might explain why maternal smoking is more closely related to preterm birth among multiparous women than among nulliparous women.

Genetic amniocentesis: a risk factor for preterm delivery?

OBJECTIVE

To determine whether genetic amniocentesis performed in the second trimester of pregnancy is associated with the risk of preterm delivery.

STUDY DESIGN

Case-control study performed in several departments of obstetrics and gynaecology of nine European countries. Three thousand and ninety-one preterm births and 5298 controls randomly selected from singleton births born at term during 1994-1997 were analysed. Logistic regression models were used to compare preterm births altogether and, separately, spontaneous preterm delivery and induced preterm delivery.

RESULTS

An increased risk of preterm delivery was found in women having second trimester genetic amniocentesis after taking account of other risk factors and confounding variables (odds ratios (OR)=1.59, 95% confidence intervals (95% CI): 1.31-1.92). The association was statistically significant and similar for spontaneous preterm delivery and induced preterm delivery.

CONCLUSION

The study shows an association between preterm delivery and genetic amniocentesis. In view of the wide use of amniocentesis, further research on the etiologic role of this prenatal diagnostic technique is needed.

Preconceptional factors associated with very low birthweight delivery in East and West Berlin: a case control study

BACKGROUND

Very low birthweight, i.e. a birthweight < 1500 g, is among the strongest determinants of infant mortality and childhood morbidity. To develop primary prevention approaches to VLBW birth and its sequelae, information is needed on the causes of preterm birth, their personal and social antecedents, and on conditions associated with very low birthweight. Despite the growing body of evidence linking sociodemographic variables with preterm delivery, little is known as to how this may be extrapolated to the risk of very low birthweight.

METHODS

In 1992, two years after the German unification, we started to recruit two cohorts of very low birthweight infants and controls in East and West Berlin for a long-term neurodevelopmental study. The present analysis was undertaken to compare potential preconceptional risk factors for very low birthweight delivery in a case-control design including 166 mothers (82 East vs. 84 West Berlin) with very low birthweight delivery and 341 control mothers (166 East vs. 175 West).

RESULTS

Multivariate logistic regression analysis was used to assess the effects of various dichotomous parental covariates and their interaction with living in East or West Berlin. After backward variable selection, short maternal school education, maternal unemployment, single-room apartment, smoking, previous preterm delivery, and fetal loss emerged as significant main effect variables, together with living in West Berlin as positive effect modificator for single-mother status.

CONCLUSION

Very low birthweight has been differentially associated with obstetrical history and indicators of maternal socioeconomic status in East and West Berlin. The ranking of these risk factors is under the influence of the political framework.

Marital status, cohabitation, and risk of preterm birth in Europe: where births outside marriage are common and uncommon

This article explores whether the impact of marital status on the risk of preterm birth varies in relation to marital practices in the population, defined by the proportion of out-of-marriage births. Data come from a case-control study of the determinants of preterm birth in 16 European countries (5456 cases and 8234 controls). There is a significantly elevated risk of preterm birth associated with both cohabitation (OR = 1.29 [1.08, 1.55]) and single motherhood (OR = 1.61 [1.26, 2.07]) for women living in countries where fewer than 20 of births occur outside marriage. In contrast, there is no excess risk associated with marital status when out-of-marriage births are more common. This overall result does not apply to all subgroups of preterm births: different patterns emerge for early preterm births and preterm births induced for medical reasons. It is important to consider social context in the analysis of individual risk factors.

Are risk factors the same for small for gestational age versus other preterm births?

OBJECTIVES

This article explores whether the impact of social and demographic risk factors for preterm birth differs for small for gestational age preterm births versus other preterm births.

STUDY DESIGN

This was a European case control study of the determinants of preterm birth (4700 cases and 6460 controls). Small for gestational age and non-small for gestational age preterm births were compared with a control group of term births; relationships were explored further by stratifying preterm births into subgroups by mode of onset, the presence of hypertension, and gestational age.

RESULTS

Of the social and demographic risk factors for preterm birth identified in this sample, high maternal age, smoking, and low and high maternal body mass index have a stronger effect on small for gestational age preterm births. In contrast, obstetric history, maternal education, and marital status have similar effects regardless of birth weight. Hypertension during pregnancy is strongly associated with small for gestational age preterm birth and contributes to an explanation of observed differences.

CONCLUSIONS

These results underline the importance of considering fetal growth restriction in the analysis of risk factors for preterm birth.

What's so bad about teenage pregnancy?

A systematic literature review identified the most frequently cited medical consequences of teenage pregnancy as anaemia, pregnancy-induced hypertension, low birth weight, prematurity, intra-uterine growth retardation and neonatal mortality. Critical appraisal suggested that increased risks of these outcomes were predominantly caused by the social, economic, and behavioural factors that predispose some young women to pregnancy. Maternal age less than 16 years was associated with a modest (1.2-2.7 fold) increase in prematurity, low birth weight and neonatal death.