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 and childhood growth trajectory: a random effects regression analysis

Background

Although maternal smoking during pregnancy has been reported to have an effect on childhood overweight/obesity, the impact of maternal smoking on the trajectory of the body mass of their offspring is not very clear. Previously, we investigated this effect by using a fixed-effect model. However, this analysis was limited because it rounded and categorized the age of the children. Therefore, we used a random-effects hierarchical linear regression model in the present study.

Methods

The study population comprised children born between 1 April 1991 and 31 March 1999 in Koshu City, Japan and their mothers. Maternal smoking during early pregnancy was the exposure studied. The body mass index (BMI) z-score trajectory of children born to smoking and non-smoking mothers, by gender, was used as the outcome. We modeled BMI trajectory using a 2-level random intercept and slope regression.

Results

The participating mothers delivered 1619 babies during the study period. For male children, there was very strong evidence that the effect of age in months on the increase in BMI z-score was enhanced by maternal smoking during pregnancy (P < 0.0001). In contrast, for female children, there was only weak evidence for an interaction between age in months and maternal smoking during pregnancy (P = 0.054), which suggests that the effect of maternal smoking during pregnancy on the early-life BMI trajectory of offspring differed by gender.

Conclusions

These results may be valuable for exploring the mechanism of fetal programming and might therefore be clinically important.Key words: body mass index, childhood growth, gender, multi-level analysis, pregnancy, smoking     

Maternal smoking during pregnancy and smoking by adolescent daughters.

OBJECTIVES. Since cigarette smoking in adolescence represents a crucial entry point in the progression to illicit drugs, risk factors for adolescent smoking have public health implications. The influence of mothers on children's smoking appears to be greater than that of fathers. To explain the selective influence of mothers, we examined the consequences of maternal smoking during pregnancy in two longitudinal samples. METHODS. Analyses were conducted on follow-up interview data from two dyadic samples of mothers and firstborn adolescents for whom data on maternal smoking during and after pregnancy were available (192 mother-child pairs originating from New York State and 797 dyads from a national sample). RESULTS. In both samples, maternal smoking during pregnancy, when postnatal smoking was controlled, selectively increased the probability that female children would smoke and would persist in smoking (adjusted odds ratios of about 4). CONCLUSIONS. The findings suggest that nicotine or other substances released by maternal smoking can affect the fetus, perhaps through the nicotinic input to the dopaminergic motivational system, so as to predispose the brain in a critical period of its development to the subsequent addictive influence of nicotine consumed more than a decade later in life.     

Maternal obesity in pregnancy and respiratory health in early childhood

Obesity is associated with systemic inflammation, immunological changes, increased risk of respiratory infections and chronic respiratory illness. Maternal obesity in pregnancy increases the risk of pregnancy complications, caesarean sections and adverse birth outcomes, which have in turn been associated with respiratory illness in children. To our knowledge, the possible influence of maternal obesity in pregnancy on respiratory illness in early childhood beyond the newborn period has not been explored. We examined the relationship between a high maternal body mass index (BMI) in pregnancy and lower respiratory tract infections and wheeze up to 18 months of age in the Norwegian Mother and Child Study (MoBa), a population-based cohort study that includes 100 000 pregnant women, conducted at the Norwegian Institute of Public Health. We analysed data from the first 33 192 children, born between 1999 and 2005.
In unadjusted analyses maternal obesity in pregnancy was related to both respiratory infections and wheeze in the children. In multivariable analyses, only an effect on wheeze remained. The risk of wheeze increased linearly with maternal BMI in pregnancy, and was 3.3% higher [95% CI 1.2, 5.3] for children with mothers who were obese during pregnancy, than for children of mothers with normal BMI. This effect was not mediated through obesity-related pregnancy complications, low birthweight, preterm birth or caesarean section.     

Maternal smoking in pregnancy, fetal development, and childhood asthma

OBJECTIVES: We examined the relationships among maternal smoking in pregnancy, fetal development, and the risk of asthma in childhood. METHODS: We conducted a population-based cohort study, where all 58 841 singleton births were followed for 7 years using nationwide registries. RESULTS: Maternal smoking increased the risk of asthma (adjusted odds ratio = 1.35; 95% confidence interval = 1.13, 1.62 for high exposure). Low birthweight and preterm delivery increased the risk of asthma at the age of 7, whereas being small for gestational age did not. CONCLUSIONS: Maternal smoking in pregnancy increases the risk of asthma during the first 7 years of life, and only a small fraction of the effect seems to be mediated through fetal growth.     

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.     

Maternal obesity and glucose intolerance during pregnancy among Mexican-Americans

Low birthweight is uncommon among Mexican-American infants, despite the substantial proportion of mothers who live in poverty. This apparent paradox has generated studies of factors protecting fetal growth, but may have masked other important health problems in the Mexican-American community. Obesity, impaired glucose tolerance and diabetes are common among Mexican-American women of childbearing age and during pregnancy. Prevalence of these conditions is two to four times higher in Mexican-American than in non-Hispanic white women. As obesity and glucose intolerance during pregnancy are associated with fetal overgrowth and increased risk of subsequent obesity and type 2 diabetes in mother and child, the adequacy of birthweight as a measure of maternal and infant risk may be obscured in populations with a high prevalence of these conditions. Their possible contribution to the increasing incidence of obesity and type 2 diabetes in Mexican-American children, adolescents and young adults has not been examined. Appropriate preconception, prenatal and follow-up care may identify high-risk women, improve weight and metabolic status and reduce the severity and impact of diabetes and its complications. However, late or no prenatal care is common among Mexican-American women and the frequency of follow-up care is unknown. As low birthweight is a major public health indicator of maternal and neonatal health, perceived 'good birth outcomes' have reduced health policy, programme and research attention to Mexican-American mothers and infants. Studies of the impact of obesity and glucose intolerance during pregnancy on the birthweights of Mexican-American infants should be undertaken, along with systematic assessment of the subsequent health status and preventive health-care needs of women and children in this population.     

Maternal smoking during pregnancy and expenditures on neonatal health care

Cigarette smoking during pregnancy substantially increases the risk of low-weight birth, and infants born to smokers weigh less, on average, than those born to nonsmokers. Low birth weight is an important predictor of neonatal morbidity and death, and the intensity of neonatal care is significantly higher for low-birth-weight infants. In this study, we estimate expenditures on neonatal care based on the relation between maternal smoking during pregnancy and the incidence of low-weight births. Our results indicate that maternal smoking during pregnancy was responsible for 35,816 low-weight births in the U.S. in 1983, or about 14.5% of all low-weight births. We also estimate that 14,977, or 6.6%, of all admissions to neonatal intensive care units were a result of maternal smoking and that these admissions cost approximately $272 million, representing 8.5% of total national expenditures on neonatal intensive care services. We estimate that the average cost of neonatal care was $288 higher for infants born to smokers than for those born to nonsmokers.     

Maternal smoking and childhood asthma.

The role of maternal smoking as a causal factor for the incidence of childhood asthma is still not clearly established. It was investigated among 3- and 4-year-old-child incident cases confirmed by a 6-year follow-up (n = 294) and cases who no longer had symptoms after diagnosis (n = 110). The study took place in Montréal, Canada, between 1988 and 1997. Persistent and transient cases were compared with their respective controls from the original case-control study of incidence. The odds ratio for heavy maternal smoking adjusted for known risk factors for asthma was 3.84 (95% confidence interval: 1.68, 8.76) among persistent cases and close to one among transient cases.     

Maternal smoking during pregnancy and school performance at age 15

BACKGROUND: Smoking during pregnancy has been suggested to have long-term consequences for neuropsychologic development in the offspring, including behavioral problems, attention deficit disorders, and antisocial behavior. Also, findings from several studies indicate an association with impaired cognitive function in the children. METHODS: In a population-based Swedish cohort study, we examined possible associations between maternal smoking in pregnancy and educational achievement in the offspring at age 15 years among more than 400,000 male and female students born 1983 through 1987. Generalized estimating equation models were used to evaluate associations of maternal smoking, other maternal characteristics, and birth characteristics with school performance. Odds ratios (ORs) were used as a measure of risk. RESULTS: In a model adjusted for maternal characteristics, maternal smoking compared with no tobacco use during pregnancy was associated with an increased risk of poor scholastic achievement: for 1-9 cigarettes per day, the OR was 1.59 (95% confidence interval = 1.59-1.63) and for 10 or more cigarettes per day, the OR was 1.92 (1.86-1.98). These risks remained unchanged when we also adjusted for smoking-related pregnancy outcomes such as fetal growth restriction and preterm birth. However, if the mother had smoked in her first pregnancy, but not in her second pregnancy, the younger sibling was also at increased risk of poor school performance. CONCLUSION: Observed associations between maternal smoking during pregnancy and poor cognitive performance in the offspring might not be causal. We suggest that associations reported in earlier studies may instead reflect the influence of unmeasured characteristics that differ between smokers and nonsmokers.     

Maternal vitamin D intake during pregnancy and early childhood wheezing

BACKGROUND: Maternal intake of vitamin D in pregnancy is a potentially modifiable but understudied risk factor for the development of asthma in children. OBJECTIVE: We investigated whether maternal vitamin D intake in pregnancy is associated with decreased risks of wheezing symptoms in young children. DESIGN: Subjects were from a birth cohort recruited in utero with the primary objective of identifying associations between maternal diet during pregnancy and asthma and allergies in children. A random sample of 2000 healthy pregnant women was recruited while attending antenatal clinics at the Aberdeen Maternity Hospital, Scotland, at approximately 12 wk gestation. Maternal vitamin D intake was ascertained from a food-frequency questionnaire completed at 32 wk of gestation. The main outcome measures were wheezing symptoms, spirometry, bronchodilator response, atopic sensitization, and exhaled nitric oxide at 5 y. RESULTS: Respiratory details through 5 y and maternal food-frequency-questionnaire data were available for 1212 children. In models adjusted for potential confounders, including the children's vitamin D intake, a comparison of the highest and lowest quintiles of maternal total vitamin D intake conferred lower risks for ever wheeze [odds ratio (OR): 0.48; 95% CI: 0.25, 0.91], wheeze in the previous year (OR: 0.35; 95% CI: 0.15, 0.83), and persistent wheeze (OR: 0.33; 95% CI: 0.11, 0.98) in 5-y-old children. In addition, lower maternal total vitamin D intakes in pregnancy were also associated with decreased bronchodilator response (P = 0.04). No associations were observed between maternal vitamin D intakes and spirometry or exhaled nitric oxide concentrations. CONCLUSION: Increasing maternal vitamin D intakes during pregnancy may decrease the risk of wheeze symptoms in early childhood.     

Maternal cigarette smoking and pregnancy outcome

Maternal smoking rates in pregnancy have declined, particularly in the non-manual social classes, and perinatal mortality rates have fallen over the last 20 years. We have therefore re-evaluated the relationship between maternal cigarette smoking and pregnancy outcome against this background. A total of 608 stillbirths and 634 infant deaths were identified using the All Wales Perinatal Survey. The cause of death was classified using the clinicopathological system. Maternal smoking rates and social class groupings were compared with those in a cohort of 16047 survivors born to women resident in South Glamorgan. The smoking rate was 37.8% in mothers of babies who died compared with 27.2% in mothers of survivors, an odds ratio (OR) of 1.63 [95% CI 1.44, 1.84]. The OR for unexplained stillbirth was 1.72 [95% CI 1.38, 2.13], placental abruption 2.07 [95% CI 1.29, 3.31], infection 3.70 [95% CI 2.23, 6.13] and sudden infant death syndrome 4.84 [95% CI 3.05, 7.69]. Maternal smoking was not associated with death due to prematurity or a congenital anomaly. Despite changes in smoking habits and the causes of perinatal death, smoking during pregnancy continues to be strongly associated with fetal and infant mortality. It is important that health promotion activities are effective in reducing smoking during pregnancy.     

Maternal smoking during pregnancy and limb reduction malformations in Sweden.

OBJECTIVE: This study was undertaken to investigate a possible connection between different types of limb reduction defects and maternal smoking during pregnancy. METHODS: With the use of the Swedish health registries, 610 cases of limb reduction malformations were selected from among 1 109 299 infants born between 1983 and 1993 with known smoking exposure in early pregnancy. Confounders such as maternal age and parity were controlled for with the use of the Mantel-Haenszel technique. RESULTS: The odds ratio for any maternal smoking among all cases of limb reductions was 1.26 (95% confidence interval = 1.06, 1.50). The main subgroups of limb reduction defects showed similar odds ratios, but in longitudinal reduction defect, only unilateral cases showed an association with maternal smoking. CONCLUSIONS: This study supports an association between maternal smoking and limb reduction malformations, but further work is needed before a causal inference can be made.     

Maternal cigarette smoking during pregnancy in relation to oral clefts

Studies on maternal smoking in relation to oral cleft defects have yielded inconsistent findings, with results ranging from no association to sixfold increases in risk. The authors examined this relation in a case-control study conducted in Boston, Massachusetts, Philadelphia, Pennsylvania, Toronto, Ontario, Canada, and the state of Iowa during the years 1983-1987, in which mothers of malformed infants were interviewed within 6 months after delivery about prenatal events and exposures. Maternal cigarette smoking during pregnancy for 400 infants with cleft lip with or without cleft palate and for 215 infants with cleft palate alone was compared with that for 2,710 infants with other malformations (controls). Relative risks (and 95% confidence intervals) were estimated for smokers of 1-14, 15-24, and greater than or equal to 25 cigarettes per day relative to never smokers; the respective estimates for cleft lip with or without cleft palate were 1.2 (95% confidence interval (CI) 0.9-1.6), 1.4 (95% CI 1.0-2.1), and 0.7 (95% CI 0.3-1.6), and for cleft palate alone, estimates were 1.0 (95% CI 0.7-1.5), 0.9 (95% CI 0.5-1.5), and 0.8 (95% CI 0.3-2.2). Relative risks were also close to unity for case subgroups divided according to the presence or absence of an associated malformation. Multivariate control of several potential confounders did not alter these estimates. Based on this large series of cases, maternal smoking during pregnancy does not appear to increase the risk of oral clefts.     

Maternal smoking during pregnancy and risks of suicidal acts in young offspring

Obstetric and neonatal complications have been associated with completed and attempted suicide (suicidal acts) in young offspring. Maternal smoking is one of the most important risk factors for obstetric complications, but the association between prenatal smoking exposure and offspring risk of suicidal acts is unknown. We performed a population-based study of 1,449,333 single births born in Sweden between 1983 and 1996, derived from linked registry data. Maternal smoking and risks of suicidal acts in offspring were estimated using hazard ratios, derived from proportional-hazard models, controlling for potential confounding of parental socio-demographic factors and psychiatric care in first degree relatives. To control for unmeasured familial confounding, a matched case-control analysis of suicidal acts was performed within sibling pairs discordant for prenatal smoking exposure. In the cohort analysis, the adjusted hazard ratio for completed suicide among offspring to women smoking 1-9 cigarettes and at least 10 cigarettes per day were 1.67, 95% confidence interval (CI), 1.29-2.16, and 1.54, 95% CI, 1.12-2.10. For suicidal acts, corresponding hazard ratios were 1.28, 95% CI 1.21-1.35 and 1.48, 95% CI 1.39-1.57, respectively. However, in sibling pairs discordant for suicidal acts and prenatal smoking exposure, we found no evidence that prenatal smoking exposure increased the risk of suicidal acts. We conclude that the association between prenatal smoking exposure and offspring risk of suicidal acts is probably confounded by unmeasured familial factors.