Maternal smoking during pregnancy and offspring IQ

BACKGROUND: Maternal smoking in pregnancy lowers birthweight. It is unclear, however, whether smoking during pregnancy lowers offspring IQ, and, if it does, whether it is through the smoking effect on fetal growth. METHOD: Representative samples of low birthweight (<2500 g) and normal birthweight children born in 1983-85 from inner-city and suburban communities in southeast Michigan, USA were assessed at ages 6, 11, and 17, using Wechsler intelligence tests. Smoking during pregnancy was ascertained from mothers at the first assessment; and smoking at any time was ascertained at the first and second assessment. Generalized estimating equation models were used, with children's IQ at all three assessments as outcomes (n = 798). RESULTS: Without adjustment, offspring of mothers who smoked during pregnancy scored 6.8 IQ points lower than offspring of mothers who never smoked, on average. Low birthweight children scored 5.4 IQ points lower than normal birthweight children, on average. The statistical association of maternal smoking with offspring IQ was confounded by maternal characteristics, chiefly, maternal cognitive ability as measured by IQ and education; adjustment for these factors eliminated the association. By contrast, adjustment for maternal IQ and education as well as smoking during pregnancy had a negligible effect on the low birthweight-related IQ deficit. Low birthweight did not mediate the association of smoking and lowered IQ in offspring. CONCLUSION: Maternal smoking during pregnancy is a proxy for a matrix of vulnerabilities for adverse child cognitive development and has no direct causal effect on child's IQ. The relationship of low birthweight and IQ is independent of maternal smoking and maternal cognitive abilities.     

Maternal smoking during pregnancy predicts nicotine disorder (dependence or withdrawal) in young adults – a birth cohort study

Objective: To investigate whether maternal smoking during pregnancy predicts offspring nicotine disorder (dependence or withdrawal) at 21 years.
Method: Participants comprised a prospective birth cohort involving 7,223 singleton children whose mothers were enrolled between 1981 and 1983 at the first antenatal visit to the Mater Mothers' Hospital, Brisbane, Queensland. The present sub-cohort consisted of 2,571 youth who completed the Composite International Diagnostic Interview-computerised version (CIDI-Auto) that assesses nicotine dependence and withdrawal according to DSM-IV diagnostic criteria at the 21-year follow-up.
Results: 12.8% of offspring met criteria for nicotine dependence and 8.5% met criteria for withdrawal. 16.6% met criteria for either dependence or withdrawal. Smoking during pregnancy resulted in offspring being more likely to have dependence or withdrawal at 21 years than offspring of mothers who never smoked (age adjusted odds ratio 1.53 (95% CI: 1.19-1.96).
Conclusions: Findings emphasise the long-term adverse effects of maternal smoking during pregnancy, including nicotine dependence in young adult offspring.
Implications: Public health approaches should strengthen arguments for mothers to cease smoking during pregnancy in view of the long-term health implications for offspring, and reinforce measures to help smokers among pregnant women and women of childbearing age to stop.     

Assessment of chronic exposure to cigarette smoke and its change during pregnancy by segmental analysis of maternal hair nicotine

This study aimed to investigate the association between biomarkers of fetal exposure to smoking during the whole pregnancy, nicotine in maternal and newborns hair samples, and quantitative measurement of smoking intake and exposure evaluated by maternal self-reported questionnaire. Study subjects were 150 mothers and their newborns from a hospital in Barcelona. A questionnaire including smoking habits was completed in the third trimester of pregnancy and on the day of delivery. Nicotine content was measured in two subsequent segments of maternal hair accounting for the first and last months of pregnancy, and in fetal hair. The geometric mean of nicotine concentration in maternal hair discriminated between nonexposition (3.84 and 2.80 ng/mg in distal and proximal hair segment, respectively) and exposition to cigarette smoke during pregnancy (6.06 and 4.30 ng/mg in distal and proximal hair segment, respectively) (P<0.05), and between these two classes and active smoking (14.40 and 11.08 ng/mg in distal and proximal hair segment, respectively). Maternal hair nicotine was able to differentiate levels of exposure to tobacco smoke and levels of intake. Nicotine concentration in hair from newborns did not differentiate between exposure and nonexposure to environmental tobacco smoke (ETS) in nonsmoking mothers. Finally, chronic exposure to cigarette smoke during pregnancy, assessed by maternal hair nicotine, correlated negatively with anthropometric parameters of newborns.     

Cord serum cotinine as a biomarker of fetal exposure to cigarette smoke at the end of pregnancy

This study investigated the association between biomarkers of fetal exposure to cigarette smoke at the end of pregnancy, cotinine in cord serum and in maternal and newborn urine samples, and quantitative measurement of smoking intake and exposure evaluated by maternal self-reported questionnaire. Study subjects were 429 mothers and their newborns from a hospital in Barcelona, Spain. A questionnaire including smoking habits was completed in the third trimester of pregnancy and on the day of delivery. Cotinine concentration in cord serum was associated with daily exposure to nicotine in nonsmokers and with daily nicotine intake in smokers. The geometric mean of cotinine concentration in cord serum statistically discriminated between newborns from nonexposed and exposed nonsmoking mothers, and between these two classes and smokers, and furthermore was able to differentiate levels of exposure to tobacco smoke and levels of intake stratified in tertiles. Urinary cotinine levels in newborns from nonsmoking mothers exposed to more than 4 mg nicotine daily were statistically different from levels in two other categories of exposure. Cotinine concentration in urine from newborns and from mothers did not differentiate between exposure and nonexposure to environmental tobacco smoke (ETS) in nonsmoking mothers. Cord serum cotinine appeared to be the most adequate biomarker of fetal exposure to smoking at the end of pregnancy, distinguishing not only active smoking from passive smoking, but also exposure to ETS from nonexposure.     

Prenatal effects of maternal smoking on daughters' smoking: nicotine or testosterone exposure?

OBJECTIVES: The purpose of this study was to specify the effect of prenatal fetal exposure to maternal cotinine and testosterone on daughters' smoking in adolescence and adulthood. METHODS: Longitudinal causal models were estimated among 240 White mother-daughter pairs from the Child Health and Development Study. Mothers and daughters were reinterviewed when daughters were aged 15 to 17 years, and daughters were interviewed at 27 to 30 years of age. Blood samples were obtained from both parents during pregnancy and from adult daughters. RESULTS: Testosterone and smoking were positively correlated among mothers during their pregnancy and among adult daughters. Maternal prenatal cotinine had no direct effect on daughters' smoking; self-reported smoking in pregnancy did have a direct effect. Smoking among daughters during adolescence was determined by maternal prenatal testosterone and self-reported maternal smoking during pregnancy and postnatally. Smoking among adult daughters reflected chronic smoking since adolescence and the continuing effect of postnatal maternal smoking. Prenatal maternal testosterone affected adult daughters' testosterone. CONCLUSIONS: Estimates of the impact of prenatal maternal smoking depend on the measure of smoking. Prenatal testosterone exposure is a previously unrecognized risk factor for smoking among female offspring.     

Maternal smoking and birth weight: interaction with parity and mother's own in utero exposure to smoking

BACKGROUND: Few studies have reported interactions between maternal smoking and other maternal characteristics and exposures. We examined maternal smoking in a cohort study for which data from 3 generations were available to examine maternal characteristics and exposures from a life-course perspective. METHODS: We had data from 3 generations: women enrolled in the U.S. Collaborative Perinatal Project (CPP) between 1959 and 1965 at the Baltimore site (G1); daughters (G2) of those G1 mothers who were followed to ages 27-33 years in the Pathways to Adulthood study; and children (G3) born to the G2 women who provided pregnancy and birth information during the Pathways study. These data allowed examination of exposures that occurred to the mother during her childhood and in utero. RESULTS: We found evidence of a 3-way interaction effect on birth weight for maternal smoking in pregnancy, maternal exposure to smoking in utero (grandmaternal smoking), and maternal parity. Maternal smoking reduced birth weight in 3 of the subgroups, with the size of the effect on birth weight moderated by parity and the mother's own in utero exposure to smoking. CONCLUSIONS: A mother's prenatal exposure to smoke may affect the birth weight of her offspring. This effect would be consistent with both the accumulation-of-risk and the fetal-programming hypotheses.     

In utero and postnatal maternal smoking and asthma in adolescence

BACKGROUND: Asthma in early childhood has been associated with maternal smoking during pregnancy and parental smoking soon after birth. However, less is known about these exposures and the development of asthma symptoms in adolescence. METHODS: Data were taken from the Mater University Study of Pregnancy, a large birth cohort study of mothers and children enrolled in Brisbane, Australia, beginning in 1981. Smoking was assessed at 2 stages during pregnancy and at the 6-month and 5-year follow-up visits. Asthma was assessed from maternal reports that were provided when the child was age 14 years. We conducted multivariable multinomial logistic regression analyses to assess the effect of maternal smoking on asthma symptoms. RESULTS: There was a strong sex interaction such that girls whose mothers had smoked heavily (20 or more cigarettes per day) in pregnancy and at the 6-month follow up had increased odds of experiencing asthma symptoms at age 14 (odds ratio = 1.96; 95% confidence interval = 1.25-3.08). The contribution of heavy smoking during pregnancy appeared to be stronger than heavy smoking after the birth. No similar associations were seen for boys. CONCLUSION: Female adolescents whose mothers smoked heavily during the fetal period and the early months of life have increased risk of asthma symptoms in adolescence. In utero exposure to heavy smoking was found to have a stronger effect than postnatal environmental tobacco exposure.     

Maternal and paternal smoking during pregnancy and risk of ADHD symptoms in offspring: testing for intrauterine effects

Maternal smoking during pregnancy is associated with attention deficit hyperactivity disorder (ADHD) in offspring. It is assumed by many that this association is causal. Others suggest that observed associations are due to unmeasured genetic factors or other confounding factors. The authors compared risks of maternal smoking during pregnancy with those of paternal smoking during pregnancy. With a causal intrauterine effect, no independent association should be observed between paternal smoking and offspring ADHD. If the association is due to confounding factors, risks of offspring ADHD should be of similar magnitudes regardless of which parent smokes. This hypothesis was tested in 8,324 children from a well-characterized United Kingdom prospective cohort study, the Avon Longitudinal Study of Parents and Children (data from 1991-2000). Associations between offspring ADHD and maternal and paternal smoking during pregnancy were compared using regression analyses. Offspring ADHD symptoms were associated with exposure to both maternal and paternal smoking during pregnancy (mothers: β = 0.25, 95% confidence interval: 0.18, 0.32; fathers: β = 0.21, 95% confidence interval: 0.15, 0.27). When paternal smoking was examined in the absence of maternal smoking, associations remained and did not appear to be due to passive smoking exposure in utero. These findings suggest that associations between maternal smoking during pregnancy and child ADHD may be due to genetic or household-level confounding rather than to causal intrauterine effects.     

Neonatal hair nicotine levels and fetal exposure to paternal smoking at home

Exposure to environmental tobacco smoke (ETS) is a major risk to human health, and the home is the greatest single source of ETS for children. The authors investigated fetal exposure to paternal smoking at home during pregnancy. Korean families were included as trios of fathers, mothers, and neonates identified in 2005-2007. Sixty-three trios were finally enrolled in this study after exclusion of those in which the mother was a smoker or was regularly exposed to ETS at places other than the home. Nicotine and cotinine concentrations in hair were measured by using liquid chromatography-tandem mass spectrometry to determine long-term exposure to ETS. The difference between neonatal nicotine concentrations in the smoker and nonsmoker groups was not statistically significant. However, in the indoor-smoker group, neonatal nicotine concentrations were significantly higher than in the outdoor and nonsmoker groups (P < 0.05). Furthermore, neonatal nicotine concentrations in the outdoor-smoker group were not different from those in the nonsmoker group. These findings indicate that paternal smoking inside the home leads to significant fetal and maternal exposure to ETS and may subsequently affect fetal health. Conversely, findings show that paternal smoking outside the home prevents the mother and her fetus from being exposed to ETS.     

Maternal smoking during pregnancy and subcutaneous fat mass in early childhood. The Generation R Study

Maternal smoking during pregnancy increases the risk of obesity in the offspring. Not much is known about the associations with other measures of body composition. We assessed the associations of maternal smoking during pregnancy with the development of subcutaneous fat mass measured as peripheral and central skinfold thickness measurements in early childhood, in a population-based prospective cohort study from early fetal life onward in the city of Rotterdam, The Netherlands. The study was performed in 907 mothers and their children at the ages of 1.5, 6 and 24 months. As compared to non-smoking mothers, mothers who continued smoking during pregnancy were more likely to have a younger age and a lower educational level. Their children had a lower birth weight, higher risk of small size for gestational age and were breastfed for a shorter duration (P-values <0.01). We did not observe differences in peripheral, central and total subcutaneous fat mass between the offspring of non-smoking mothers, mothers who smoked in first trimester only and mothers who continued smoking during pregnancy (P > 0.05). Also, the reported number of cigarettes smoked by mothers in both first and third trimester of pregnancy were not associated with peripheral, central and total subcutaneous fat mass in the offspring at the ages of 1.5, 6 and 24 months. Our findings suggest that fetal exposure to cigarette smoke during pregnancy does not influence subcutaneous fat mass in early childhood. Follow-up studies are needed in children at older ages and to identify associations of maternal smoking during pregnancy with other measures of body composition.     

Breastfeeding duration and perinatal cigarette smoking in a population-based cohort

OBJECTIVES: We examined the association between breastfeeding duration and maternal smoking before, during, and after pregnancy. METHODS: Data from the 2000-2001 Oregon Pregnancy Risk Assessment Monitoring System were used. Early weaning was defined as not breastfeeding at 10 weeks postpartum. RESULTS: At 10 weeks after pregnancy, 25.7% of mothers who initiated breastfeeding no longer breastfed. After controlling for confounders, quitters (mothers who quit smoking during pregnancy and maintained quit status after pregnancy) and postpartum relapsers (mothers who quit smoking during pregnancy and resumed smoking after delivery) did not have significantly higher risk for early weaning than nonsmokers. However, persistent smokers (mothers who smoked before, during, and after pregnancy) were 2.18 times more likely not to breastfeed at 10 weeks (95% confidence interval=1.52, 2.97). Women who smoked 10 or more cigarettes per day postpartum (i.e., heavy postpartum relapsers and heavy persistent smokers) were 2.3-2.4 times more likely to wean their infants before 10 weeks than were nonsmokers. CONCLUSIONS: Maternal smoking is associated with early weaning. Stopping smoking during pregnancy and decreasing the number of cigarettes smoked postpartum may increase breastfeeding duration.     

Bias in maternal reports of smoking during pregnancy associated with fetal distress

BACKGROUND: Studies examining the adverse effects of smoking during pregnancy commonly use maternal reports. We hypothesized that if an adverse event occurred during pregnancy, women may underreport smoking. This study looked for bias in maternal report of smoking if fetal distress occurs. METHODS: Data were collected prospectively from patients attending The MotheRisk Program who smoked during pregnancy, and were categorized by delivery outcome, maternal and neonatal characteristics, and the raw number of cigarettes smoked per day during pregnancy reported at clinic and at follow-up. The difference between these two values was compared. RESULTS: 95 women had uneventful deliveries and 25 had fetal distress. Women who reported fetal distress decreased their report of smoking after delivery compared to their original report during pregnancy, whereas women with an uneventful labour did not (p = 0.04). CONCLUSIONS: Our results suggest that if an adverse pregnancy outcome occurs, mothers may tend to underreport their cigarette consumption.     

孕妇被动吸烟与小于胎龄儿关系的Meta分析

目的 探讨孕妇孕期被动吸烟与小于胎龄儿之间的关系,分析不同孕期和不同地点被动吸烟的效应.方法 利用Meta分析方法综合分析国内外8篇关于孕妇孕期被动吸烟与小于胎龄儿关系的回顾性研究文献.结果 孕妇孕期被动吸烟与小于胎龄儿之间的粗合并效应值OR=1.45(95%CI:1.05～2.01),调整合并效应值OR=1.76(95%CI:1.15～2.69);孕妇孕早期被动吸烟的合并效应值OR=1.85(95%CI:1.25～2.72),孕中晚期被动吸烟的合并效应值OR=2.12(95%CI:1.43～3.13);家庭和工作中被动吸烟与小于胎龄儿之间的关系均没有统计学意义.结论 孕妇孕期被动吸烟可增加发生小于胎龄儿的危险性.除了家庭和工作环境外,还应注意其他环境的被动吸烟.     

Association of self-reported passive smoking in pregnant women with cotinine level of maternal urine and umbilical cord blood at delivery

Passive smoking during pregnancy leads to adverse effects on mother and infant. The present investigation was designed to evaluate the association between maternal reported passive smoking with the cotinine concentration of maternal urine and umbilical cord blood at delivery and to determine the accuracy of maternal reporting of exposure to cigarette smoke during pregnancy. This was a cross-sectional study. From the 108 non-smoker pregnant women who were referred for delivery, 54 were passive smokers. Urine samples were collected from the mothers in the delivery room and blood samples after birth were taken from the umbilical cord. Passive smoking was evaluated through questionnaire and cotinine level of urine and umbilical cord blood. The geometric mean cotinine concentration of the maternal urine and the umbilical cord serum were, respectively, 27.4 ± 29.96 ng/mL and 3.71 ± 1.22 ng/mL in the exposed group (P < 0.001) and 0.75 ± 2.29 and 0.40 ± 0.63 in the non-exposed group (P < 0.001). There was a statistically significant correlation between maternal urinary and umbilical cord serum level of cotinine (P < 0.001, r = 0.58). Significant associations were shown between maternal reports of exposure to cigarette smoking with cotinine level of urine (kappa = 96%) and umbilical cord (kappa = 98%) (P < 0.001). This study shows that the pregnant woman's report of passive smoking during pregnancy in Iran is accurate. The questionnaire is an appropriate method to evaluate smoke exposure and could replace cotinine measurement.     

A dose-response relationship between maternal smoking during late pregnancy and adult intelligence in male offspring

An association between maternal smoking during pregnancy and cognitive and behavioural development has been observed in several studies, but potential effects of maternal smoking on offspring adult intelligence have not been investigated. The objective of the present study was to investigate a potential association between maternal smoking during pregnancy and offspring intelligence in young adulthood. Adult intelligence was assessed at the mean age of 18.7 years by a military draft board intelligence test (Borge Priens Prove) for 3044 singleton males from the Copenhagen Perinatal Cohort with information regarding maternal smoking during the third trimester coded into five categories (about 50% of the mothers were smokers). The following potential confounders were included as covariates in multivariable analyses: parental social status and education, single mother status, mother's height and age, number of pregnancies, and gestational age. In separate analyses, birthweight and length were also included as covariates. Maternal cigarette smoking during the third trimester, adjusted for the seven covariates, showed a negative association with offspring adult intelligence (P=0.0001). The mean difference between the no-smoking and the heaviest smoking category amounted to 0.41 standard deviation, corresponding to an IQ difference of 6.2 points [95% confidence interval 0.14, 0.68]. The association remained significant when further adjusted for birthweight and length (P=0.007). Both unadjusted and adjusted means suggested a dose-response relationship between maternal smoking during pregnancy and offspring adult intelligence. When subjects with missing data were excluded, essentially the same results were obtained in the reduced sample (n=1829). These results suggest that smoking during pregnancy may have long-term negative consequences on offspring adult intelligence.     

Maternal cigarette smoking and invasive meningococcal disease: a cohort study among young children in metropolitan Atlanta, 1989-1996

OBJECTIVES: This study assessed the association between maternal cigarette smoking during pregnancy and the risk of invasive meningococcal disease during early childhood. METHODS: Using a retrospective cohort study design, cases from an active surveillance project monitoring all invasive meningococcal disease in the metropolitan Atlanta area from 1989 to 1995 were merged with linked birth and death certificate data files. Children who had not died or acquired meningococcal disease were assumed to be alive and free of the illness. The Cox proportional hazards analysis was used to assess the independent association between maternal smoking and meningococcal disease. RESULTS: The crude rate of meningococcal disease was 5 times higher for children whose mothers smoked during pregnancy than for children whose mothers did not smoke (0.05% vs 0.01%). Multivariate analysis revealed that maternal smoking (risk ratio [RR] = 2.9; 95% confidence interval [CI] = 1.5, 5.7) and a mother's having fewer than 12 years of education (RR = 2.1; 95% CI = 1.0, 4.2) were independently associated with invasive meningococcal disease. CONCLUSIONS: Maternal smoking, a likely surrogate for tobacco smoke exposure following delivery, appears to be a modifiable risk factor for sporadic meningococcal disease in young children.     

Maternal smoking, social class and outcomes of pregnancy

Exposure to tobacco during pregnancy is an important risk factor for infant health. Recently the prevalence of smoking during pregnancy has declined in our area. The objective of this study was to analyse the association between several social variables and the fetal exposure to smoking, as well as the association between maternal smoking and some adverse gestational outcomes. Data collection was cross-sectional. The study population were women in the city of Barcelona (Catalonia, Spain) delivering a child without birth defects. The sample corresponded to the controls of the Birth Defects Registry of Barcelona, 2% of all pregnancy deliveries in the city from 1994 to 2003 (n = 2297). Information sources were hospital records and a personal interview of mothers. The analysis measured first the association between independent variables (instruction level, social class, occupation, nationality, planned pregnancy, parity, hospital funding and smoking status of the mother's partner) with two dependent variables: smoking at the initiation of pregnancy and quitting during pregnancy. Second, the persistence of smoking over pregnancy and all independent variables were studied with three variables indicating adverse outcomes of pregnancy: low gestation, low birthweight and intrauterine growth restriction (IUGR). Finally, the joint association between the persistence of smoking over pregnancy and social class taken as independent variables was determined with the three variables indicating adverse outcomes of pregnancy. Logistic regression models were fitted, adjusting for maternal age. Results are presented as odds ratios with their 95% confidence intervals. The prevalence of smoking at the onset of gestation was 41%, and 40% of these women quit during pregnancy, so that 25% delivered as active smokers. Fewer women with higher educational levels and from families with non-manual jobs smoked, as did immigrants, those planning pregnancy and women whose partner did not smoke. Smoking immigrants quit more frequently than nationals, as did those planning pregnancy, primiparae, and women whose partner did not smoke. Low gestation, low birthweight and IUGR were more frequent among smokers and women with a manual occupation, but manual occupation lost its significance when adjusting for smoking. The association between smoking and adverse results was higher for IUGR. In conclusion, the prevalence of smoking and quitting during pregnancy varied according to social factors. The influence of social factors on the outcome of pregnancy was mediated strongly by smoking in a country that provides access to health care free of cost. A priority in reducing inequalities in health is to help women from manual work backgrounds quit smoking.     

Maternal alcohol and coffee drinking, parental smoking and childhood leukaemia: a French population-based case-control study

We investigated the role of maternal alcohol and coffee drinking during pregnancy and that of parental smoking in the aetiology of childhood leukaemia. A French, population-based, case-control study was conducted, comparing 472 [407 acute lymphoblastic leukaemia (ALL) and 62 acute myeloblastic leukaemia] cases of childhood acute leukaemia (AL) and 567 population controls, frequency-matched with cases on age, gender and region of residence. Both case and control mothers filled in a comprehensive self-administered standardised questionnaire, eliciting detailed data on maternal alcohol and coffee consumption during pregnancy and parental smoking before, during and after pregnancy. Maternal alcohol consumption of more than 1 drink per day was related to ALL (OR = 2.8 [95% CI 1.8, 5.9]). While maternal coffee consumption was not significantly related to AL (OR = 1.4 [95% CI 0.9, 2.3]), highest intake of coffee (more than 3 cups per day) during pregnancy was associated with AL in children whose mothers were non-smokers (OR = 1.9 [95% CI 1.0, 3.5]). No association with parental smoking, either maternal or paternal, was observed with AL. The present results suggest a possible role of the highest consumption of alcohol by the mother during pregnancy in the aetiology of childhood AL.     

The influence of active and passive smoking during pregnancy on umbilical cord blood levels of vitamins A and E and neonatal anthropometric indices

Smoking during pregnancy has been shown to be detrimental for the developing fetus. The effects of active and passive maternal smoking on umbilical cord serum levels of vitamin A and vitamin E were examined. Secondary measures included anthropometric parameters in the newborn. Maternal and umbilical cord serum levels of vitamins A and E were measured at delivery. The mothers were assigned to three groups: non-smoking (n 12); passive smoking (n 13); active smoking (n 18). Based on multivariate linear regressions, active smoking during pregnancy was associated with increased umbilical cord serum levels of vitamin A and vitamin E. While enhanced circulating levels of vitamin A in cord blood were also found in non-smoking mothers exposed to tobacco smoke during pregnancy, those of vitamin E were not influenced. Further, an inverse association between smoking behaviour during pregnancy and birth length was observed, with shortest length in active smokers followed by passive smoking mothers. Active and passive maternal smoking behaviour during pregnancy increases the fetal demand for antioxidant compounds in order to counteract the oxidative burden by cigarette smoke. Against this background, the observed increase in umbilical cord serum levels of vitamins A and E may subserve antioxidative processes in response to tobacco smoke-induced oxidative stress. This would reduce the availability of vitamins A and E for fetal maturation, which is critical inasmuch as both compounds are indispensable for the developing fetus. However, due to the cross-sectional nature of our observation, this line of reasoning definitely requires validation in cause-effect experiments in the future.     

Maternal smoking and low birthweight: implications for antenatal care.

The incidence of low birthweight has been related to smoking prevalence in each social group using published data for 1984. The attributable risk of low birthweight has been estimated, based on a relative risk of 2 for mothers who smoke during pregnancy. Assuming 12.5% of cigarette smokers stopped smoking during pregnancy, 18.1% of all low weight births were caused by maternal smoking in 1984. The percentage for most social groups was similar. The overall attributable risk from smoking was estimated to be 12.7 low weight births per 1000 total births, with a further 12.1 per 1000 due to other factors acting in a socioeconomic gradient. We estimate that the minimum attainable low birthweight incidence in 1984 was 45.4 per 1000 total births, based on the lowest observed incidence, corrected for smoking prevalence, which was in social group II. We recommend the addition of maternal smoking information to the Korner maternity clinical options data set, to enable an accurate assessment of the risks and to provide local monitoring of initiatives to reduce smoking prevalence during pregnancy.