Factors associated with term low birthweight in Cardiff, Wales

Dose-response relationships of maternal height and weight with risk of low birthweight neonates: a meta-analysis

INTRODUCTION

The development of novel methods to identify pregnant women at increased risk of low birthweight neonates before delivery is required to improve pre- and periconceptional strategies to reduce the prevalence of low birthweight neonates. A dose-response meta-analysis was performed to examine the adjusted relationships of maternal height and weight with risk of low birthweight neonates.

EVIDENCE ACQUISITION

PubMed (Medline), CINAHL, PsycINFO, Wiley Online Library, ProQuest, Web of Science, Google Scholar, and Sage Journals Online were searched. There were no restrictions regarding publication date. English-language cohort studies involving singleton births that provided adjusted relative risks or Odds Ratios for low birthweight neonates at two or more values of maternal height or weight compared to the reference and numbers of low birthweight neonates and numbers of normal birthweight neonates in these values and the reference are included.

EVIDENCE SYNTHESIS

From the five finally eligible studies, four good-quality studies evaluating the relationship of maternal height with risk of low birthweight neonates and three good-quality studies evaluating the relationship of maternal weight with risk of low birthweight neonates were extracted. Both of these relationships were non-linear rather than linear (P values for non-linearity <0.05). Based on the non-linear dose-response model, maternal height limited to below 160 cm and maternal weight with no restrictions regarding the range were significantly and negatively related to risk of low birthweight neonates.

CONCLUSIONS

Risk of low birthweight neonates may decrease with increasing maternal height from below 160 cm to 160 cm and by increasing maternal weight regardless of above or below 55 kg.

Maternal smoking status during pregnancy and low birth weight in offspring: systematic review and meta-analysis of 55 cohort studies published from 1986 to 2020

BACKGROUND

Maternal smoking during pregnancy may be associated with low birth weight (LBW) in offspring and global risk estimates have not been summarized previously. We aimed to systematically explore evidence regarding maternal smoking and the LBW risk in offspring globally and examine possible causes of heterogeneity across relevant studies.

METHODS

Comprehensive search of PubMed, Ovid Embase, Ovid Medline (R), and Web of science from inception until October 2021 was carried out. A random-effects meta-analysis was used to estimate the pooled odds ratio (OR) and corresponding 95% confidence interval (CI). Restricted cubic spline analysis with three knots was used to further examine the dose-response relationship.

RESULTS

Literature searches yielded 4940 articles, of which 53 met inclusion criteria (comprising 55 independent studies). Maternal smoking during pregnancy was significantly associated with the risk of LBW in offspring (OR = 1.89, 95% CI = 1.80-1.98). Furthermore, an obvious dose-response relationship between the amount of cigarettes daily smoked in pregnancy and the risk of LBW in offspring was observed. The results of subgroup analyses indicated that the risk of maternal smoking on LBW was larger in more recently conducted studies (P = 0.020) and longer period of active smoking during pregnancy (P = 0.002). No evidence of publication bias was found.

CONCLUSIONS

In summary, maternal smoking in pregnancy was significantly associated with a higher risk of LBW in offspring on a global scale. The risk of maternal smoking on infant LBW seems to be increasing over time, and was higher with longer smoking duration throughout pregnancy and more cigarettes smoked daily.

Maternal smoking during pregnancy and the risk of congenital urogenital malformations: A systematic review and meta-analysis

BACKGROUND

Investigations regarding the association between maternal smoking and specific urogenital teratogenesis exist. However, an integrated systematic review and meta-analysis studying the relationship by encompassing the whole urogenital system is essential.

OBJECTIVE

Even though many studies about inborn urogenital malformations have been conducted, its etiologic factors and exact pathogenesis are still unclear. Our aim is to assess the risk of congenital urogenital malformations in offspring of smoking pregnant women.

RESULTS

The meta-analysis, covering 41 case-control and 11 cohort studies, suggested that maternal smoking was associated with an increased risk of urogenital teratogenesis (odds ratio [OR] = 1.13, 95% confidence interval [CI]: 1.04-1.23, p = 0.005), cryptorchidism (OR = 1.18, 95%CI: 1.12-1.24, p = 0.0001), hypospadias (OR = 1.16, 95%CI: 1.01-1.33, p = 0.039), and kidney malformations (OR = 1.30, 95%CI: 1.14-1.48, p = 0.0001). Moreover, paternal smoking during the mother's pregnancy was also significantly associated (OR = 1.26, 95%CI: 1.03-1.55, p = 0.028). The association between smoking > 10 cigarettes/day was evident but was not significant (OR = 1.24, 95%CI:0.81-1.88, p = 0.323).

CONCLUSION

Our results showed that maternal smoking during pregnancy increased the risk of congenital urogenital malformations. In numerous epidemiological studies, maternal smoking during pregnancy has a significant role in fetal development. Therefore, quitting tobacco use may be an effective method for reducing the risk of congenital urogenital malformation in pregnant women.

Differential correlations between maternal hair levels of tobacco and alcohol with fetal growth restriction clinical subtypes

Maternal exposure to tobacco and alcohol is a known cause, among others, for fetal growth restriction (FGR). Clinically, FGR can be subclassified into two forms: intrauterine growth restriction (IUGR) and small for gestational age (SGA), based on the severity of the growth retardation, and abnormal uterine artery Doppler or cerebro-placental ratio. This study aimed at investigating any differential correlation between maternal exposures to these toxins with the two clinical forms of FGR. Therefore, a case-control study was conducted in Barcelona, Spain. Sixty-four FGR subjects, who were further subclassified into IUGR (n = 36) and SGA (n = 28), and 89 subjects matched appropriate-for-gestational age (AGA), were included. The levels of nicotine (NIC) and ethyl glucuronide (EtG), biomarkers of tobacco and alcohol exposure, respectively, were assessed in the maternal hair in the third trimester. Our analysis showed 65% of the pregnant women consumed alcohol, 25% smoked, and 19% did both. The odds ratios (ORs) of IUGR were 21 times versus 14 times for being SGA with maternal heavy smoking, while with alcohol consumption the ORs for IUGR were 22 times versus 37 times for the SGA group. The differential correlations between these toxins with the two subtypes of FGR suggest different mechanisms influencing fetal weight. Our alarming data of alcohol consumption during pregnancy should be considered for further confirmation among Spanish women.

Waist-to-hip ratio versus body mass index as predictors of fitness in women

The claim that men prefer women with low waist-to-hip ratios (WHR) has been vigorously disputed. We examine self-report data from 359 primiparous Polish women (with normal singleton births and healthy infants) and show that WHR correlates with at least one component of a woman's biological fitness (her first child's birth weight, a variable that significantly affects infant survival rates). However, a woman's Body Mass Index (BMI) is a better predictor of her child's neonatal weight in small-bodied women (<54 kg). The failure to find a preference for low WHR in some traditional populations may thus be a consequence of the fact that, even in western populations, body mass is a better predictor of fitness in those cases characterized by low maternal body weight.

The intergenerational effects on birth weight and its relations to maternal conditions, São Paulo, Brazil

Background and Objectives. Parents' birth weight acts as a predictor for the descendant birth weight, with the correlation more strongly transmitted through maternal line. The present research aims to study the correlation between the child's low or increased birth weight, the mother's birth weight, and maternal conditions. Methods. 773 mother-infant binomials were identified with information on both the baby's and the mother's birth weight recorded. Group studies were constituted, dividing the sample according to birth weight (<2,500 grams (g) and ≥3,500 grams (g)). The length at birth was also studied in children ≤47.5 cm (lower quartile). Chi² test or Fisher's exact test, Spearman's Rho, and odds ratio were performed in order to investigate the relation between the children's weight and length at birth and the mothers' and children's variables. Results. The girls were heavier at birth than their mothers, with an average increase at birth weight between the generations of 79 g. The child's birth weight <2,500 g did not show any correlation with maternal birth weight <2,500 g (Fisher 0.264; Spearman's Rho 0.048; OR 2.1 and OR lower 0.7) or with maternal stature below the lower quartile (<157 cm) (Chi² sig 0.323; with Spearman's Rho 0.036; OR 1.5 and OR lower 0.7). The child's low birth weight (<2,500 g) was lightly correlated with drug use by the mother during pregnancy (Fisher 0.083; Spearman's Rho 0.080; OR 4.9 and OR lower 1.0). The child's birth weight <2,500 g showed increased correlation with gestational age lower than 38 weeks and 3 days (Chi² sig 0.002; Spearman's Rho 0.113; OR 3.2 and OR lower 1.5). The child's weight at birth ≥3,500 g showed strong correlation with maternal weight at birth ≥3,500 g (Chi² sig 0; Spearman's Rho +0.142; OR 0.5 and OR upper 0.7). It was also revealed that the higher the maternal prepregnancy BMI, the stronger the correlation with child's birth weight ≥3,500 g ((maternal prepregnancy BMI > 25.0 with Chi² sig 0.013; Spearman's Rho 0.09; OR 1.54 and OR upper 2.17) and (maternal prepregnancy BMI > 30.0 with Chi² sig 0 Spearman's Rho 0.137; OR 2.58 and OR upper 4.26)). The child's length at birth in the lower quartile (≤47.5 cm) showed strong correlation with drug use by the mother during pregnancy (Chi² sig 0.004; Spearman's Rho 0.105; OR 4.3 and OR lower 1.5). Conclusions. The mother's increased weight at birth and the prenatal overweight or obesity were correlated with increased weight and length at birth of the newborn, coupled with the tendency of increasing birth weight between generations of mothers and daughters. Also, descendants with smaller length at birth are the children of women with the lowest statures.

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

OBJECTIVE

Preterm birth (PTB) and low birth weight (LBW) are the leading causes of neonatal morbidity and mortality, but the effect of maternal height on these outcomes continues to be debated. Our objective was to determine the relationships between maternal height and PTB and LBW.

DATA SOURCES

Medline and EMBASE were searched from their inceptions.

STUDY SELECTION

Studies with a reference group that assessed the effect of maternal height on PTB (< 37 weeks) and LBW (< 2500 grams) in singletons were included.

DATA EXTRACTION

Data were extracted independently by two reviewers.

DATA SYNTHESIS

Fifty-six studies were included involving 333 505 women. In the cohort studies, the unadjusted risk of PTB in short-statured women was increased (relative risk [RR] 1.23; 95% CI 1.11 to 1.37), as was the unadjusted risk of LBW (RR 1.81; 95% CI 1.47 to 2.23), although not all of the studies with adjusted data found the same association. Maternal tall stature was not associated with PTB (unadjusted RR 0.97; 95% CI 0.82 to 1.14), although LBW was decreased (unadjusted RR 0.56; 95% CI 0.46 to 0.69), but not in the adjusted data.

CONCLUSION

From our complete systematic review and meta-analyses, to our knowledge the first in this area, we conclude that short-statured women have higher unadjusted risks of PTB and LBW and tall women have approximately one half the unadjusted risk of LBW of women of reference height.

Current pattern of Ponderal Indices of term small-for-gestational age in a population of Nigerian babies

Background

Small-for-gestational age (SGA) newborns constitute a special group of neonates who may have suffered varying degrees of intrauterine insults and deprivation. Variations in birth weight, length and Ponderal Index (PI) depend on the type and degree of intrauterine insults the babies were exposed to. The objective of the study was to determine the current prevalence of term SGA births in a Nigerian Tertiary Hospital and the current pattern of Ponderal Indices among term SGA in a population of Nigerian babies.

Methods

Subjects comprised of consecutive term singleton mother-baby pairs in the first 24 hours of life. It was a cross sectional study. The anthropometric parameters of each baby were recorded and the PI was also determined.

Results

Out of 1,052 live births during the study period (September to December, 2009), 825 were term, singleton babies. Five hundred and eight-one babies (70.4%) fall into the upper socio-economic classes 1 and II, 193 (23.4%) in the middle class and 51 (6.2%) were of the lower classes IV and V. None of the mothers indicated ingestion of alcohol or smoking of cigarette. Fifty-nine babies (7.2%) were small-for gestational age (SGA). Of the 59 SGA subjects, 26 (44.1%) were symmetrical SGA while 33 (55.9%) were asymmetrical SGA. There was no significant sex or socioeconomic predilection for either symmetrical or asymmetrical growth (p = 0.59, 0.73 respectively).

Conclusion

The findings showed that proportionality in SGA fetuses is a continuum, with the PI depending on the duration of intrauterine insult and the extent of its effects on weight and length before delivery.

Factors that affect maternal insulin resistance and modify fetal growth and body composition

Fetal growth is multifactorial and can be altered by a variety of extrinsic and intrinsic factors. The maternal, placental, and fetal contribution to growth must all be considered. Of particular interest are maternal metabolic regulation and the availability of nutrients to the developing fetus. Weight gain, hyperlipidemia, and insulin resistance occur as a normal adaptation to pregnancy. Obesity and underlying insulin resistance among women of reproductive age are rapidly increasing, and the contribution of pregnancy on this abnormal metabolic background poses additional maternal and fetal challenges. Many components of the metabolic syndrome have been associated with changes in fetal growth, including obesity, dyslipidemia, hypertension, and insulin resistance or glucose intolerance. Additional factors affect fetal growth and include diet, exercise, and smoking. In this review, we briefly discuss the importance and descriptions of fetal growth, followed by a discussion of several of the extrinsic and intrinsic established factors affecting fetal growth. We highlight factors that may modify fetal growth and body composition directly or indirectly through alterations in maternal metabolism.

Prenatal smoking among adolescents and risk of fetal demise before and during labor

STUDY OBJECTIVE

To investigate the relationship between smoking during pregnancy and the occurrence of stillbirth phenotypes among adolescent mothers.

DESIGN

Retrospective cohort

SETTING

Singleton births in Missouri from 1978 through 1997.

PARTICIPANTS

Two groups of "younger" (<15 years) and "older" (15-19 years) adolescent mothers were compared to "mature" mothers (age 20-24 years).

MAIN OUTCOME MEASURES

Cox Proportional Hazards Regression models generated adjusted risk estimates of the association between intrauterine nicotine exposure and the risk of total, antepartum, and intrapartum stillbirth in each age group.

RESULTS

Approximately 32% (N=205,887) of the total 633,849 singleton births analyzed were among adolescent mothers. The overall prevalence of smoking was 31.2%, with the lowest prevalence (14.1%) among the youngest mothers while older adolescents had the highest (31.7%). The risk for intrapartum stillbirth among smoking adolescents <15 years of age was twice the risk for older adolescent and mature mothers. The risk of intrapartum stillbirth among smokers decreased as maternal age increased: [adjusted hazard ratio (AHR), 95% confidence interval (CI) for young mothers: 4.0, 95%CI=0.6-28.7; for older adolescents AHR=1.5, 95%CI=1.1-2.1 and for mature mothers AHR=1.8, 95% CI=1.4-2.2], respectively.

CONCLUSIONS

In utero tobacco exposure has maternal age-related differential and lethal effects on the fetus. Young maternal age tends to potentiate these effects. There is a public health need to develop appropriate smoking cessation messages targeted specifically to this high risk group.

Assessment of risk factors for infantile cataracts using a case-control study: National Birth Defects Prevention Study, 2000-2004

OBJECTIVE

To identify risk factors for infantile cataracts of unknown etiology.

DESIGN

Case-control study.

PARTICIPANTS

Case infants (n = 152) and control infants (n = 4205) enrolled in the National Birth Defects Prevention Study for birth years 2000-2004.

METHODS

Multivariate analysis was performed exploring associations for risk factors for bilateral and unilateral infantile cataracts of unknown etiology.

MAIN OUTCOME MEASURES

Infantile cataracts of unknown etiology.

RESULTS

Maternal interviews were completed for 43 case infants with bilateral and 109 with unilateral infantile cataracts of unknown etiology. Very low birth weight (<1500 g) was associated with both unilateral (adjusted odds ratio [OR], 6.0; 95% confidence interval [CI], 2.2-16.3) and bilateral (OR, 13.2; 95% CI, 4.2-41.1) cataracts, whereas low birth weight (1500-2499 g) was only associated with bilateral cataracts (OR, 3.3; 95% CI, 1.3-8.1). Infants with unilateral cataracts were more likely to be born to primigravid women (OR, 1.6; 95% CI, 1.0-2.7) than women with > or =2 previous pregnancies, although this was of borderline significance. Although not significant, effect estimates were elevated suggesting a possible association between unilateral cataracts and maternal substance abuse during pregnancy, and between bilateral cataracts and urinary tract infection during pregnancy and aspirin use during pregnancy.

CONCLUSIONS

Very low birth weight is associated with both bilateral and unilateral cataracts, whereas low birth weight is associated with bilateral cataracts and primigravidity with unilateral cataracts. Other associations, although not statistically significant, suggest risk factors that merit further research.

Cigarette exposure induces changes in maternal vascular function in a pregnant mouse model

Smoking is associated with multiple adverse pregnancy outcomes, including fetal growth restriction. The objective of this study was to determine whether cigarette smoke exposure during pregnancy in a mouse model affects the functional properties of maternal uterine, mesenteric, and renal arteries as a possible mechanism for growth restriction. C57Bl/CJ mice were exposed to whole body sidestream smoke for 4 h/day. Smoke particle exposure was increased from day 4 of gestation until late pregnancy (day 16-19), with mean total suspended particle levels of 63 mg/m(3), representative of moderate-to-heavy smoking in humans. Uterine, mesenteric, and renal arteries from late-pregnant and virgin mice were isolated and studied in a pressure-arteriograph system (n = 23). Plasma cotinine was measured by ELISA. Fetal weights were significantly reduced in smoke-exposed compared with control fetuses (0.88 +/- 0.1 vs. 1.0 +/- 0.08 g, P < 0.02), while litter sizes were not different. Endothelium-mediated relaxation responses to methacholine were significantly impaired in both the uterine and mesenteric vasculature of pregnant mice exposed to cigarette smoke during gestation. This difference was not apparent in isolated renal arteries from pregnant mice exposed to cigarette smoke; however, relaxation was significantly reduced in renal arteries from smoke-exposed virgin mice. In conclusion, we found that passive cigarette smoke exposure is associated with impaired vascular relaxation of uterine and mesenteric arteries in pregnant mice. Functional maternal vascular perturbations during pregnancy, specifically impaired peripheral and uterine vasodilation, may contribute to a mechanism by which smoking results in fetal growth restriction.

The risk of intrapartum stillbirth among smokers of advanced maternal age

BACKGROUND/AIM

The effects of advanced maternal age and smoking in pregnancy on fetal survival have previously been reported. However, whether advanced maternal age modifies the relationship between smoking in pregnancy and intrapartum stillbirth remains unknown. We therefore set out to determine the impact of advanced maternal age (> or =35 years) on the association between smoking during pregnancy and intrapartum stillbirth by employing retrospective analysis of birth registry data.

METHODS

We used a cohort of singleton births in Missouri from 1978 through 1997 (N = 1,436,628) to compute the risk of total, antepartum, and intrapartum stillbirth in smoking mothers. We categorized mothers into two age groups: "younger" (<35 years), and "older" (> or =35 years). Non-smoking mothers age <35 years were the referent category. Cox regression models were used to generate independent measures of association between intrauterine tobacco exposure and the risk of total, antepartum, and intrapartum stillbirth in each age group.

RESULTS

A total of 5,772 counts of stillbirth were identified, yielding a stillbirth rate of 4.0 per 1,000. Approximately 33% (N = 1,900) occurred among older smokers resulting in a stillbirth rate of 9.1 per 1,000. The probability of intrapartum stillbirth was greatest among older smokers, followed by younger smokers and lowest among younger non-smokers (P < 0.01). As compared to non-smoking younger gravidas, younger smoking mothers had a 30% greater likelihood for both antepartum and intrapartum stillbirth (adjusted hazard ratio [95% confidence interval]: 1.3 [1.2-1.4] and 1.3 [1.2-1.5], respectively). Among older smokers the risk for intrapartum stillbirth was three times that of the referent group (adjusted hazard ratio: 3.2, 95% confidence interval: 2.2-4.5).

CONCLUSIONS

The risk of intrapartum stillbirth associated with smoking in pregnancy is potentiated by the age of the mother. This information will help policy makers develop targeted smoking cessation campaigns and positively impact quit rates in older mothers.

Documenting and comparing plant species diversity by using numerical and parametric methods in Khaje Kalat, NE Iran

The aim was to examine and document several aspects of numerical diversity such as species richness, species diversity and evenness and to compare diversity in different slope aspects of the area by using numerical and parametric methods. About 193 quadrats of 4 m2 were located according to the nature of vegetation. Species composition and their abundance were recorded in a two-year period (2005 to 2006). The result of field investigation was collecting and identifying of the total 225 plant species belonging to 154 genera and 37 families. The abundance data were subjected to analyses by specific diversity packages to characterize and obtain numerical indices (Shannon, Simpson, Brillouin, McIntosh, etc.,) and parametric families of species diversity. Numerical indices were calculated and documented for monitoring purposes. The results of diversity in main slope aspects (N, S, E, W) showed higher species richness and species diversity indices in the north aspect than in the others but it was not true with evenness indices. About 30 species such as Acanthophyllum glandulosum, Acroptilon repens, Alcea tiliacea, Bromus sericeous, Astragalus turbinatus, Centaurea balsamita etc., were detected exclusively in the north aspect. This can be important in reducing the evenness. Diversity comparing by using rank-abundance plot as well as diversity ordering of Hill, Renyi and Patil and Taillie confirmed high species diversity in the north yet the result of ANOVA showed no significant differences in the four aspects. The result of diversity based on the models revealed that the whole area, the south and the west aspects follow lognormal distribution, north aspect follows logarithmic whereas the east follows both lognormal and logarithmic distribution. In other word, a shift from being lognormal to logarithmic model was observed in the east aspect.

Social class inequalities in perinatal outcomes: Scotland 1980-2000

OBJECTIVE

To examine social class inequalities in adverse perinatal events in Scotland between 1980 and 2000 and how these were influenced by other maternal risk factors.

DESIGN

Population based study using routine maternity discharge data.

SETTING

Scotland.

PARTICIPANTS

All women who gave birth to a live singleton baby in Scottish hospitals between 1980 and 2000 (n=1,282,172).

MAIN OUTCOME MEASURES

Low birth weight (LBW), preterm birth, and small for gestational age (SGA).

RESULTS

The distribution of social class changed over time, with the proportion of mothers with undetermined social class increasing from 3.9% in 1980-84 to 14.8% in 1995-2000. The relative index of inequality (RII) decreased during the 1980s for all outcomes. The RII then increased between the early and late 1990s (LBW from 2.09 (95%CI 1.97, 2.22) to 2.43 (2.29, 2.58), preterm from 1.52 (1.44, 1.61) to 1.75 (1.65, 1.86), and SGA from 2.28 (2.14, 2.42) to 2.49 (2.34, 2.66) respectively). Inequalities were greatest in married mothers, mothers aged over 35, mothers taller than 164 cm, and mothers with a parity of one or more. Inequalities were also greater by the end of the 1990s than at the start of the 1980s for women of parity one or more and for mothers who were not married.

CONCLUSION

Despite decreasing during the 1980s, inequalities in adverse perinatal outcomes increased during the 1990s in all strata defined by maternal characteristics.

Smoking habits, nicotine use, and congenital malformations

OBJECTIVE

We examined whether maternal smoking and use of nicotine substitutes during the first 12 weeks of pregnancy increased the prevalence of congenital malformations in general and of certain congenital malformations in particular.

METHODS

In the Danish National Birth Cohort (1997-2003) we identified 76,768 pregnancies (and their subsequent singleton births); 20,603 were exposed to tobacco smoking during the first 12 weeks of pregnancy. Birth outcomes were collected by linkage to the Central Population Register, the National Patients Register, and the National Birth Register. We identified congenital malformations from the Hospital Medical Birth Registry as they were recorded at birth or in the first year of follow-up.

RESULTS

Smoking mothers were younger, weighed less, consumed more alcohol, and had received less education. Children exposed to prenatal tobacco smoking had no increase in congenital malformations prevalence compared with the nonexposed children in both crude and adjusted analyses. Children born to nonsmokers, but who used nicotine substitutes, had a slightly increased relative congenital malformations prevalence ratio; relative prevalence rate ratio was 1.61 (95% confidence interval 1.01-2.58), which represents a 60% increased risk. When the analysis was restricted to musculoskeletal malformations, the relative prevalence rate ratio was 2.63 (95% confidence interval 1.53-4.52).

CONCLUSION

Our results showed no increase in congenital malformations related to prenatal tobacco smoking. However, we identified an increase of malformations risk in nonsmokers using nicotine substitutes. This finding needs to be replicated in other data sources.

LEVEL OF EVIDENCE

II-2.

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.

Changing patterns of inequality in birthweight and its determinants: a population-based study, Scotland 1980-2000

Birthweight is used as an indicator of individual and population health and is known to be strongly correlated with adult cardiovascular disease. This paper uses routinely collected maternity discharge data from Scotland between 1980 and 2000 to look at birthweight trends and the changes in the distribution of maternal risk factors for birthweight. We also examine the contributions of each of the risk factors to birthweight trends and investigate whether there has been a reduction in inequality in birthweight over time. Data from 1,282,172 singleton live births were used in the analysis. Both mean birthweight and low birthweight (LBW:<2500 g) were used as outcomes. The risk factors studied were maternal age, parity, maternal height, marital status and occupational social class of the father. The slope and relative indices of inequality were used to measure the change in inequalities over time. Mean birthweight increased from 3320 g in 1980 to 3410 g in 2000, while the percentage LBW decreased slightly from 5.7% in 1980 to 5.4% in 2000. The prevalence of many risk factors changed; there has been an increase in the proportion of older mothers, single mothers, taller mothers and mothers with undetermined social class. Although most risk factors had a significant change in effect over time, the inequalities in birthweight between groups did not appear to diminish over time. Both the slope and relative index of inequality had a quadratic relationship over time, with the inequalities in birthweight being greatest in the early 1980s and late 1990s.

Levels of excess infant deaths attributable to maternal smoking during pregnancy in the United States

OBJECTIVES

The objectives of the study were: 1) To determine the risk of infant mortality associated with prenatal cigarette smoking; 2) To assess whether the relationship, if existent, was dose-dependent; 3) To explore the morbidity pathway that explains the effect of tobacco smoke on infant mortality, and 4) to compute excess infant deaths attributable to maternal smoking in the United States.

METHODS

Retrospective cohort study on 3,004,616 singleton live births that occurred in 1997 in the United States using the US national linked birth/infant death data. Excess infant deaths due to maternal smoking were computed using the population-attributable risk (PAR).

RESULTS

Overall, 13.2% of pregnant women who delivered live births in 1997 smoked during pregnancy. The rate of infant mortality was 40% higher in this group as compared to nonsmoking gravidas (P < 0.0001). This risk increased with the amount of cigarettes consumed prenatally in a dose-dependent fashion (p for trend < 0.0001). Small-for-gestational age rather than preterm birth is the main mechanism through which smoking causes excess infant mortality. We estimated that about 5% of infant deaths in the United States were attributable to maternal smoking while pregnant, with variations by race/ethnicity. The proportion of infant deaths attributable to maternal smoking was highest among American Indians at 13%, almost three times the national average. If pregnant smokers were to halt tobacco use a total of 986 infant deaths would be averted annually.

CONCLUSIONS

Smoking during pregnancy accounts for a sizeable number of infant deaths in the United States. This highlights the need for infusion of more resources into existing smoking cessation campaigns in order to achieve higher quit rates, and substantially diminish current levels of smoking-associated infant deaths.

Maternal concentration of polychlorinated biphenyls and dichlorodiphenyl dichlorethylene and birth weight in Michigan fish eaters: a cohort study

BACKGROUND

Studies on maternal exposure to polychlorinated biphenyls (PCBs) reported inconsistent findings regarding birth weight: some studies showed no effect, some reported decreased birth weight, and one study found an increase in weights. These studies used different markers of exposure, such as measurement of PCBs in maternal serum or questionnaire data on fish consumption. Additionally maternal exposures, such as dichlorodiphenyl-dichloroethylene (DDE), which are related to PCB exposure and may interfere with the PCB effect, were rarely taken into account.

METHODS

Between 1973 and 1991, the Michigan Department of Community Health conducted three surveys to assess PCB and DDE serum concentrations in Michigan anglers. Through telephone interviews with parents, we gathered information on the birth characteristics of their offspring, focusing on deliveries that occurred after 1968. We used the maternal organochlorine (OC) measurement closest to the date of delivery as the exposure. Although one mother may have contributed more than one child, serum concentrations derived from measurements in different surveys could vary for different children from the same mother. The maternal DDE and PCB serum concentrations were categorized as follows: 0 -< 5 microg / L, 5 -< 15 microg / L, 15 -< 25 microg / L, >or=25 microg / L. Using repeated measurement models (Generalized Estimation Equation), we estimated the adjusted mean birth weight controlling for gender, birth order, gestational age, date of delivery as well as maternal age, height, education, and smoking status.

RESULTS

We identified 168 offspring who were born after 1968 and had maternal exposure information. We found a reduced birth weight for the offspring of mothers who had a PCB concentration >or=25 microg / L (adjusted birth weight = 2,958 g, p = 0.022). This group, however, was comprised of only seven observations. The association was not reduced when we excluded preterm deliveries. The birth weight of offspring was increased in women with higher DDE concentrations when controlling for PCBs; however, this association was not statistically significant.

CONCLUSION

Our results contribute to the body of evidence that high maternal serum PCB concentration may reduce the birth weight in offspring. However, only a small proportion of mothers may actually be exposed to PCB concentrations >or=25 microg / L.

Pharmacological treatment for pregnant women who smoke cigarettes

Smoking has been associated with several concerns in pregnancy including miscarriage, preterm delivery and stillbirth. Unfortunately, approximately 12% of the pregnant population continue to smoke cigarettes, suggesting a need for additional therapy beyond behavioural change. This paper reviews the literature on the use of nicotine replacement therapy and bupropion (Zyban^®) in the pregnant human population, the pharmacokinetics of nicotine in the pregnant woman, and current guidelines for smoking cessation for pregnant patients. There are currently four studies that have investigated the use of nicotine patch, three for nicotine gum, and registry and preliminary reports for bupropion. These studies did not show any adverse pregnancy outcomes with the use of pharmacological aid for smoking cessation. All the nicotine replacement therapy studies, with the exception of one randomized-controlled nicotine patch trial had small sample sizes and looked at short-term use of drug in the third trimester. Two studies have examined the pharmacokinetics of nicotine in the pregnant woman. The results from these studies reveal greater nicotine metabolism in pregnant individuals who continue to smoke during pregnancy. Current guidelines from several organizations uniformly recommend that Nicotine Replacement Therapy should be considered if non-pharmacological therapies have been unsuccessful. Bupropion is recommended in pregnancy if the benefits outweigh the risks. There is a need for further studies on the safety and effectiveness of Nicotine Replacement therapy and bupropion in pregnancy. However, considering the current research and guidelines, pharmacological cessation aids should be considered if non-pharmacological therapies have not been effective.

Where and to what extent is prevention of low birth weight possible?

Law birth weight (LBW), due to shortened gestation and/or inadequate fetal growth. is the major determinant of infant mortality and morbidity. Despite improvements in infant mortality, them has been no reduction in LBW rates. The authors examined the relationship between 33 maternal characteristics and the increased risks of preterm (PT) delivery or small-for-gestational-age (SGA) births in 76,444 Alberta women 1994-1997. PT was associated with preexisting medical conditions, obstetrical history, and pregnancy complications. Modifiable factors such as advanced maternal age contributed only 11% to the overall PT risk. SGA births were associated with several modifiable factors, including low prepregnancy weight, maternal age, smoking, drinking, and drug dependency. These contributed to 29% and 31% of PTand term SGA births. Smoking remains an important target for intervention, having contributed to 8% of PT births and about 24% of SGA births. SGA appears to be more amenable to prevention than PT delivery.

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.

The increase in very-low-birthweight infants in Germany: artefact or reality?

Earlier findings have shown that after unification with the Federal Republic of Germany (FRG) in October 1990 the proportion of very-low-birthweight infants in the former German Democratic Republic (GDR) increased. This study seeks to explore this observation in more detail at the regional level. The analysis of aggregate data of live births in Germany between 1991 and 1997 shows an increasing proportion of very-low-birthweight infants as well as a general trend towards heavier babies in both east and west. The growing proportion of live born infants at very low birthweights in the east, however, seems to be due, in part, to increased registration, most likely reflecting the introduction of the more comprehensive (western) definition of a live birth with unification in October 1990. A fairly distinct east-west pattern in the birthweight distribution present in 1991 had almost disappeared by 1997 and given way to a north-south one.

A prospective twin study of birth weight discordance and child problem behavior

BACKGROUND

We investigated whether low birth weight constitutes a causal risk factor for child problem behavior, using a variation of the co-twin control method.

METHODS

In a representative sample of 745 twin pairs (monozygotic: 324 pairs), birth weight was recorded at birth and child problem behavior at mean age 10 years was measured with the Child Behaviour Checklist (CBCL).

RESULTS

Lower birth weight was a continuous risk factor for later child problem behavior (adjusted regression coefficient over units of 500 g: beta = -.15, p =.046), and greater levels of within-pair CBCL discordance did not result in a reduced effect size. Greater within-pair birth weight discordance was associated with greater within-pair CBCL score discordance (beta =.35, p <.001). This latter effect was similar in monozygotic (beta =.34, p =.005) and dizygotic twins (beta =.37, p =.003).

CONCLUSIONS

The fact that (1) the effect size of the association between low birth weight and child problem behavior was not reduced in pairs with greater levels of CBCL discordance, and (2) similar effect sizes were found in monozygotic and dizygotic twins for the within-pair association between birth weight discordance and CBCL score discordance, suggests that the observed relationship between low birth weight and child problem behavior is not due to a shared environmental or genetic variable that influences both characteristics. Lower birth weight is a causal risk factor for child problem behavior, the effects of which may well extend into adulthood.

The effect of the increasing prevalence of maternal obesity on perinatal morbidity

OBJECTIVE

In this study, we assessed the temporal trends and relative and attributable perinatal risks of maternal obesity over a 20-year period.

STUDY DESIGN

We conducted a retrospective cohort study between 1980 and 1999 by using a computerized perinatal database of all women who received prenatal care and delivered their infants within a regional health care system. The main outcome measures were as follows: (1) annual mean body weight and the percentage of women classified as obese at the first prenatal visit (primary definition > or = 200 lb; secondary definitions > or = 250 lb, > or = 300 lb, body mass index > 29 kg/m(2)); and (2) relative and attributable risks of obesity for selected maternal and perinatal morbidities in successive 5-year periods.

RESULTS

From 1980 to 1999, the mean maternal weight of women at the first prenatal visit increased 20% (144-172 lb), as did the percentage of women > or = 200 lb (7.3-24.4), the percentage > or = 250 lb (1.9-10.7), the percentage > or = 300 lb (0.5-4.9), and the percentage with a body mass index > 29 kg/m(2) (16.3-36.4), P < .01 for all. Controlling for maternal age, race, and smoking status, obese women were at increased risk at each period for cesarean delivery (range of adjusted relative risk, 1.5-1.8), gestational diabetes (range, 1.8-2.9), and large (> 90th percentile) for gestational age infants (range, 1.8-2.2). From the earliest 5-year period (1980-1984) to the most recent (1995-1999), the percentage of obesity-attributable cesarean deliveries more than tripled from 3.9 to 11.6. Similar percentage increases were observed for the obesity-attributable risks for gestational diabetes (12.8-29.6) and large for gestational age infants (6.5-19.1). Trends for secondary obesity definitions were similar, although the magnitude of the increased attributable risks was smaller.

CONCLUSIONS

Efforts to reduce the frequency of certain perinatal morbidities will be constrained unless effective measures to prevent, or limit the risks of, maternal obesity are developed and implemented.

Neonatal mortality rates in communities with small maternity units compared with those having larger maternity units

OBJECTIVE

To compare neonatal mortality in geographical areas where most deliveries occur in large hospitals with areas where a larger proportion of deliveries occur in small maternity units.

DESIGN

Population-based study using data from The Norwegian Medical Birth Registry.

SETTING

Records on all deliveries in Norway from 1967 to 1996, a total of 1.7 million births, were equipped with data on the size of the maternity units used by delivering women in that particular area.

MAIN OUTCOME MEASURE

Risk of neonatal death.

RESULTS

Women living in areas where the most frequently used delivery unit had less than 2000 annual deliveries had 1.2 fold the risk of experiencing neonatal death of their newborn (95% CI 1.1-1.3). The relative risk of neonatal death in geographical areas where more than 75% of deliveries occurred in units with more than 3000 annual births was 0.8 (95% CI 0.7-0.9) compared with areas where none delivered in such large units. The relative risk of neonatal death in areas where the most frequently used delivery units had less than 100 annual births was 1.4 (95% CI 1.1-1.7) compared with areas where units of more than 3000 annual births were the most frequently used. Differences in outcome could not be explained by differences in travelling distance to an urban centre where most referral delivery units are located, differences between rural and urban municipalities, or by differences in biological or socio-economic risk factors between municipalities.

CONCLUSIONS

We observed a small but significantly decreased neonatal mortality in areas where the great majority of births occurred in large hospitals.

Risk factors for low birthweight in north-east Brazil: the role of caesarean section

Caesarean section (CS) delivery is associated with low birthweight (LBW) in south-east Brazil. A hospital-based study was conducted on singleton infants from mothers residing in São Luís, to assess if an association between CS and LBW was found in the northern part of the country, where the CS rate is lower than in the south-east. A standardised questionnaire was administered to a sample of 2541 mothers in 10 hospitals, representing 94% of all deliveries, from March 1997 to February 1998. In a logistic model, type of delivery was the independent variable, the other variables were treated as confounders, and interaction terms were added between type of delivery and all other factors. LBW was associated with low maternal height, maternal smoking, primiparity, previous LBW, public insurance, preterm birth and CS. The CS rate was 33.7%. The risk of CS was higher for primiparous and married mothers, those with high level of schooling and attended by the same physician during prenatal and delivery care, deliveries held in private hospitals, daylight hours or evenings, and for those mothers who had adequate prenatal care. Because it appears unlikely that only medical reasons are operative, it is a possibility that CS could cause LBW, reflecting abusive indications for elective CS.

Pregnancy outcomes and community health: the POUCH study of preterm delivery

In light of the social/ethnic disparity in preterm delivery (PTD) rates, the Pregnancy Outcomes and Community Health (POUCH) Study takes a broad view of the determinants of PTD by attempting to link underlying biological and psychosocial factors. The relationships between placental pathology, maternal biomarkers, and antecedent psychosocial factors are evaluated in three hypothesised pathways of PTD - one characterised primarily by infection, one by maternal vascular disease, and one by premature elevations in corticotropin releasing hormone in the absence of histological evidence of placental pathology. Within each pathway, an emphasis is placed on understanding the roles of stress and of maternal serum alpha-fetoprotein, an early biomarker associated with PTD. The POUCH Study enrolls pregnant women from five Michigan communities. Information about these women and their environments is gathered through detailed interviews and collection of biological samples including hair, urine, saliva, blood, vaginal fluid, and vaginal smear at 15-26 weeks of gestation. We have chosen to focus on the second trimester--a time when pathological processes may have evolved to a detectable stage, but generally before the onset of biological changes that accompany labour. This focus is consistent with the long-range goal of early detection/intervention and prevention of PTD.

Origins of fetal growth restriction

Regulation of growth of the fetus and its placenta begins before pregnancy. Early in pregnancy the mother sets the rate of growth of the fetus on a trajectory, which may be modified by events later in pregnancy. Low maternal weight for height, history of previous small babies, maternal undernutrition, pregnancy disorders, e.g. pre-eclampsia, are associated with low birthweight. Maternal smoking is a major factor in developed countries; infections and undernutrition in developing countries.Recently, there has been emphasis on adverse long-term outcomes including ischaemic heart disease, hypertension and diabetes associated with poor fetal growth. Experimental studies in animals show that some of these outcomes can readily be induced by restriction of fetal growth. Progress in determining successful treatments to improve the growth of the fetus has lagged behind these epidemiological and experimental findings. However, nutrient supplements improve growth in undernourished women and smoking cessation also improves fetal size and outcome.

Maternal cigarette smoking during pregnancy and infant ponderal index at birth in the Swedish Medical Birth Register, 1991-1992

OBJECTIVES

This study examined the effect of maternal smoking during pregnancy on infant body proportion.

METHODS

The ponderal index, defined as birthweight divided by crown-heel length cubed, was examined in 207,607 infants from the Swedish Medical Birth Register for 1991 and 1992.

RESULTS

Infant ponderal index was used as the outcome variable in an ordinary least squares continuous regression, which included early pregnancy smoking status, gestational age, and birthweight among the predictors. Ponderal index increased by 0.030 (+/- 0.0014) among infants of moderate smokers and by 0.040 (+/- 0.0017) among infants of heavy smokers, showing a dose response.

CONCLUSIONS

Smoking differentially alters the trajectory of weight vs length growth in the fetus.

Short-term health and economic benefits of smoking cessation: low birth weight

OBJECTIVES

To estimate excess direct medical costs of low birth weight from maternal smoking and short-term cost savings from smoking cessation programs before or during the first trimester of pregnancy.

METHODS

Simulations using data on neonatal costs per live birth. Outcome measures are mean US excess direct medical cost per live birth, total excess direct medical cost, reductions in low birth weight, and savings in medical costs from an annual 1 percentage point drop in smoking prevalence among pregnant women.

RESULTS

Mean average excess direct medical cost per live birth for each pregnant smoker (in 1995 dollars) was $511; total cost was $263 million. An annual drop of 1 percentage point in smoking prevalence would prevent 1300 low birth weight live births and save $21 million in direct medical costs in the first year of the program; it would prevent 57,200 low birth weight infants and save $572 million in direct medical costs in 7 years.

CONCLUSIONS

Smoking cessation before the end of the first trimester produces significant cost savings from the prevention of low birth weight.

Sociodemographic determinants of low birthweight in Greece: a population study

A total population sample of 10,654 singleton births from the Greek National Perinatal Survey of April 1983 was analysed to identify factors independently associated with low birthweight (LBW). The sample was divided into two groups according to the gravidity of the mothers (3368 primigravidae and 7286 multigravidae). Data examined included regional characteristics, marital status, age at and duration of marriage, parental ages at delivery, crowding in the home, insurance status, parental occupational classification and parental education levels. Logistic regression was used to define the socio-economic and demographic characteristics independently associated with the delivery of an LBW singleton baby. Significantly different LBW rates were found among the two groups: 4.3% in the primigravidae and 5.2% for multigravidae. For primigravidae significant associations were found with marital status, maternal occupation and father's education, while for multigravidae significant features were mother's education and place (region) of residence. The study showed little to assist in devising strategies of primary prevention of LBW in Greece.