Biomedical subjects

Sven Cnattingius

Publications and source records attributed to Sven Cnattingius.

At least 19 recordsLinked to original sources

PubMed2007

Incidence of hospitalization for postpartum psychotic and bipolar episodes in women with and without prior prepregnancy or prenatal psychiatric hospitalizations.

CONTEXT: Postpartum psychosis occurs in 1 to 2 cases per 1000 live births. Most studies have not distinguished postpartum psychosis from bipolar disorder or the proportion of the incidence attributable to prepregnancy psychiatric morbidity. OBJECTIVE: To determine the incidence of postpartum psychosis and bipolar disorder attributable to previous psychiatric hospitalization. DESIGN: Population-based study using linked registry data to determine postpartum onset of psychotic and bipolar episodes within 90 days after the first birth, by women with and without prepregnancy or prenatal psychiatric hospitalization. We assessed the type, number, and recency of previous hospitalizations on the incidence of hospitalization for postpartum psychotic and bipolar episodes. SETTING: Nationwide Swedish Hospital Discharge and Medical Birth registers. PATIENTS: Swedish women delivering a first live infant between January 1, 1987, and December 31, 2001. MAIN OUTCOME MEASURES: Postpartum hospitalization for psychosis or bipolar disorder. RESULTS: The cumulative incidences for postpartum psychotic and bipolar episodes (adjusted for age at first birth) were 0.07% and 0.03%, respectively. The incidence of psychiatric hospitalizations for postpartum psychotic or bipolar episodes among women without previous psychiatric hospitalizations was 0.04% and 0.01% of first births, respectively; for women with any psychiatric hospitalization before delivery, the incidence was 9.24% and 4.48%, respectively. For postpartum psychotic and bipolar episodes, the risk increased significantly with the recency of prepregnancy hospitalizations, number of previous hospitalizations, and length of most recent hospitalization. More than 40% of women hospitalized during the prenatal period for a bipolar or a psychotic condition were hospitalized again during the postpartum period. Approximately 90% of all postpartum psychotic and bipolar episodes occurred within the first 4 weeks after delivery. CONCLUSIONS: Almost 10% of women hospitalized for psychiatric morbidity before delivery develop postpartum psychosis after their first birth. This underscores the need for obstetricians to assess history of psychiatric symptoms and, with pediatric and psychiatric colleagues, to optimize the treatment of mothers with psychiatric diagnoses through childbirth.

Adult↗

PubMed2006

Will an adverse pregnancy outcome influence the risk of continued smoking in the next pregnancy?

OBJECTIVE: The purpose of this study was to study the effect of pregnancy outcomes on risks of continued smoking in subsequent pregnancy. STUDY DESIGN: Cohort study of first and second single births among 98,778 Swedish women who were daily smokers in first pregnancy. RESULTS: In all, 70.2% of women continued to smoke in second pregnancy. Compared with women with a previous normal pregnancy outcome, risk of smoking in second pregnancy was increased among women with a previous small-for-gestational-age birth (adjusted odds ratio [OR], 95% CI 1.28 [95% CI 1.19-1.37]), and reduced among women who had experienced a stillbirth (OR 0.76 [95% CI 0.63-0.93]) or an infant death because of congenital malformations (OR 0.67 [95% CI 0.49-0.92]. A previous preterm birth, Sudden Infant Death Syndrome, and other causes of infant death did not influence risk. CONCLUSION: A previous adverse pregnancy outcome has only a modest influence on smoking habits in the successive pregnancy.

Adult↗

PubMed2006

Interpregnancy weight change and risk of adverse pregnancy outcomes: a population-based study.

BACKGROUND: Maternal obesity has been positively associated with risk of adverse pregnancy outcomes, but evidence of a causal relation is scarce. Causality would be lent support if temporal changes in weight affected risk of adverse pregnancy outcomes. METHODS: We examined the associations between change in prepregnancy body-mass index (BMI) from the first to the second pregnancies, and the risk of adverse outcomes during the second pregnancy in a nationwide Swedish study of 151 025 women who had their first two consecutive singleton births between 1992 and 2001. FINDINGS: Compared with women whose BMI changed between -1.0 and 0.9 units, the adjusted odds ratios for adverse pregnancy outcomes for those who gained 3 or more units during an average 2 years were: pre-eclampsia, 1.78 (95% CI 1.52-2.08); gestational hypertension 1.76 (1.39-2.23); gestational diabetes 2.09 (1.68-2.61); caesarean delivery 1.32 (1.22-1.44); stillbirth 1.63 (1.20-2.21); and large-for-gestational-age birth 1.87 (1.72-2.04). The associations were linearly related to the amount of weight change and were also noted in women who had a healthy prepregnancy BMI for both pregnancies. INTERPRETATION: These findings lend support to a causal relation between being overweight or obese and risks of adverse pregnancy outcomes. Additionally they suggest that modest increases in BMI before pregnancy could result in perinatal complications, even if a woman does not become overweight. Our results provide robust epidemiological evidence for advocating weight loss in overweight and obese women who are planning to become pregnant and, to prevent weight gain before pregnancy in women with healthy BMIs.

Adult↗

PubMed2006

Association of cytochrome P450 1B1 polymorphism with first-trimester miscarriage.

OBJECTIVE: To determine whether the cytochrome P450 1B1 (CYP1B1) Val432Leu polymorphism is associated with risk of miscarriage. We also analyzed the possible interaction between this polymorphism and caffeine intake. DESIGN: The population-based case-control study included 507 women with miscarriage in the first trimester of pregnancy and 908 controls with a normal first-trimester pregnancy. The controls were frequency matched to cases. The material was analyzed taking maternal age, smoking habits, alcohol intake, caffeine intake, fetal karyotype, nausea, and vomiting into consideration. SETTING: University hospital and primary care facility. MAIN OUTCOME MEASURE(S): CYP1B1 Val432Leu genotype frequencies in cases and controls. RESULT(S): Carriers of the CYP1B1 432 Val/Val genotype were at a higher risk of miscarriage in the first trimester of pregnancy (odds ratio = 1.46; 95% confidence interval, 1.02-2.08). We also found a significant interaction between genotype and caffeine intake. CONCLUSION(S): CYP1B1 Val432Leu polymorphism is associated with first-trimester miscarriage, and it may also modify the risk among coffee drinkers.

Abortion, Spontaneous↗

PubMed2006

Familial aggregation of small-for-gestational-age births: the importance of fetal genetic effects.

OBJECTIVE: This study was undertaken to disentangle the maternal genetic, fetal genetic, and environmental effects for the risk of having small-for-gestational-age (SGA) offspring. STUDY DESIGN: By cross-linking the population-based Swedish Multi-Generation and Medical Birth Registers, we extracted 2,193,142 births between 1973 and 2001 with both parents identified. Odds ratios (OR) were calculated to estimate the relative risks, and generalized linear mixed models were used to estimate the contribution of genetic and environmental effects. RESULTS: Women whose full sisters had an offspring born SGA had a significantly increased risk of having a SGA offspring themselves (OR = 1.8, 95% CI 1.7-1.9), whereas the corresponding risk for brothers was lower (OR = 1.3, 95% CI 1.2-1.4). Thirty-seven percent of the liability was explained by fetal (including both maternal and paternal) genetic effects and 9% by maternal genetic effects. CONCLUSION: Genetic factors account for almost half of the liability to have SGA births. These effects are primarily caused by fetal genes.

Female↗

PubMed2006

Self-reported nicotine exposure and plasma levels of cotinine in early and late pregnancy.

BACKGROUND: The accuracy of maternal self-reported smoking information, especially exposure to environmental tobacco smoke, has been questioned. This study aimed to validate self-reported smoking, smoking cessation, and environmental tobacco smoke exposure in early and late pregnancy, using the biomarker cotinine as the gold standard. METHODS: Prospective cohort study of 953 pregnant Swedish women between 1996 and 1998. In-person interviews and cotinine measurements were performed at 6-12 and 31-34 completed weeks of gestation. All women were asked about nicotine exposures throughout pregnancy, including cigarette smoking, oral snuff, nicotine replacement therapy, and environmental tobacco smoke exposure. RESULTS: The validity of self-reported daily smoking was high in early and late pregnancy. However, among women reporting smoking cessation before the first interview and between the first and second interviews, 13% and 25% misreported active smoking, respectively. According to cotinine measurements, 22% of non-smoking women were exposed to environmental tobacco smoke in early pregnancy, and 8% were exposed in late pregnancy. Self-reported information on environmental tobacco smoke exposure in early and late pregnancy misclassified most exposed women as unexposed. CONCLUSION: The results of this study indicate that self-reported smoking information among pregnant women can be trusted. However, among women reporting smoking cessation during pregnancy, the misclassification rate increased with recency of quitting. Environmental tobacco smoke exposure was common among non-smokers, and the low validity of self-reported environmental tobacco smoke exposure suggests that future studies on environmental tobacco smoke exposure and risks of pregnancy outcomes may have to rely on biomarker assessments.

Cotinine↗

PubMed2006

Environmental tobacco smoke and risk of spontaneous abortion.

BACKGROUND: Studies of exposure to environmental tobacco smoke (ETS) and risk of spontaneous abortion are limited to a few studies of self-reported exposure, and the results have been inconsistent. The aim of this study was to investigate risk of early spontaneous abortion related to ETS and active smoking as defined by plasma cotinine levels. METHODS: We conducted a population-based case-control study in Uppsala County, Sweden, between January 1996 and December 1998. Cases were 463 women with spontaneous abortion at 6 to 12 completed weeks of gestation, and controls were 864 pregnant women matched to cases according to the week of gestation. Exposure status was defined by plasma cotinine concentrations: nonexposed, <0.1 ng/mL; ETS-exposed, 0.1-15 ng/mL; and exposed to active smoking, >15 ng/mL. Multivariable analysis was used to estimate the relative risk of spontaneous abortion associated with exposure to ETS and active smoking. RESULTS: Nineteen percent of controls and 24% of cases were classified as having been exposed to ETS. Compared with nonexposed women, risk of spontaneous abortion was increased among both ETS-exposed women (adjusted odds ratio = 1.67; 95% confidence interval = 1.17-2.38) and active smokers (2.11; 1.36-3.27). We could not show a differential effect of exposure to ETS or active smoking between normal and abnormal fetal karyotype abortions. CONCLUSIONS: Nonsmoking pregnant women exposed to ETS may be at increased risk of spontaneous abortion. Given the high prevalence of ETS exposure, the public health consequences of passive smoking regarding early fetal loss may be substantial.

Abortion, Spontaneous↗

PubMed2006

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.

Adolescent↗

PubMed2006

Risks of repeated miscarriage.

There is a lack of well-designed epidemiological studies of possible risk factors for repeated miscarriage. In this Swedish population-based case-control study, we investigated the association between sociodemographic and anthropometric factors, obstetric history and life-style factors, with respect to the risks of first-trimester repeated miscarriage. Information on maternal characteristics was collected through in-person interviews. Plasma blood samples were analysed for cotinine and folate concentrations. Adjusted odds ratios (OR) with 95% confidence interval [CI] were used to estimate the relative risk of repeated miscarriage. The risks of repeated miscarriage were increased for women aged > or = 35 years (adjusted OR 2.9 [95% CI 1.4, 5.8]), as well as for women aged < or = 24 years (OR 2.8 [95% CI 1.1, 6.8]). Women with a history of at least one preceding miscarriage prior to the two index pregnancies, women reporting prolonged time to conceive, and women with a history of myoma, faced a more than fourfold increased risk of repeated miscarriage. Smokers were at an increased risk of repeated miscarriage (OR 2.1 [95% CI 1.1, 4.1]). Among non-smoking women with high caffeine intake, there was an increased risk of repeated miscarriage, whereas there was no such association among smokers. Low plasma folate levels were not associated with increased risks.

Abortion, Spontaneous↗

PubMed2006

A prospective study of the transient decrease in ovarian cancer risk following childbirth.

Epidemiologic evidence shows that the risk of ovarian cancer is decreased following childbirth. We examined the time points when the decreased risk of postpartum maternal ovarian cancer reaches the lowest point and whether the protective effect diminishes over time. A case-control study nested within the Swedish Fertility Register included 10,086 cases of epithelial ovarian cancer recorded in the Swedish Cancer Register from 1961 to 2001. From the Fertility Register, 49,249 eligible subjects matched to the cases by age were selected as controls. The analysis contrasted risk between adjacent parities through logistic regression models that included indicator variables representing each year of age, age at delivery, and time since delivery. Compared with nulliparous women, uniparous women had a transient decrease in maternal ovarian cancer risk at 2 years after delivery (spline-derived odds ratio, 0.71; 95% confidence interval, 0.53-0.95, for those delivered at age 25 years) and maintained a lower risk for 4 years postpartum. Similar transient decreases were observed in biparous women compared with uniparous women and in women with three parities compared with biparous women. The protective effect of childbearing seemed to diminish with time. The transient decrease in postpartum ovarian cancer risk may define the latent period required for pregnancy hormones in clearing out ovarian cells that have undergone early stages of malignant transformation. The period before the risk increases again could indicate the period required for ovarian cancer induction.

Adolescent↗

PubMed2006

Birth characteristics and risk of low intellectual performance in early adulthood: are the associations confounded by socioeconomic factors in adolescence or familial effects?

OBJECTIVE: In this study we investigated whether the association between measures of fetal growth restriction and intellectual performance was mediated by socioeconomic or familial factors. METHODS: This was a population-based cohort study of 357,768 Swedish males born as singletons without congenital malformations between 1973 and 1981. The main outcome measure was intellectual performance at military conscription. RESULTS: Compared with men born with appropriate birth weight for gestational age, men born light for gestational age suffered an increased risk of low intellectual performance after adjustment for maternal and socioeconomic factors. The increase in risk of low intellectual performance related to a decrease in birth weight for gestational age was similar between families and within families. Men born short or with a small head circumference for gestational age were also at increased risk of low intellectual performance, both when adjusting for maternal and socioeconomic factors and within families. CONCLUSIONS: We found that all of the studied dimensions of restricted fetal growth are independently associated with increased risks of low intellectual performance and that these associations are only partly mediated by socioeconomic or familial factors.

Adolescent↗

PubMed2006

Risks for low intellectual performance related to being born small for gestational age are modified by gestational age.

OBJECTIVE: We sought to study whether the association between being born small for gestational age and risk for low intellectual performance was modified by gestational age. METHODS: A population-based cohort study was conducted of 352,125 boys who were born between 28 and 43 completed weeks of gestation from 1973 to 1981 in Sweden. Risk for low intellectual performance at military conscription, estimated as odds ratios with 95% confidence intervals was measured. RESULTS: Compared with men who were born preterm (28-36 weeks) and had normal birth weight for gestational age, men who were born preterm and had a very low birth weight for gestational age were not at increased risk for low intellectual performance. In contrast, men who were born preterm with a very short birth length or a very small head circumference for gestational age faced a near doubled risk for low intellectual performance compared with their appropriate peers. Among men who were born at term (37-41 weeks), risk for low intellectual performance was increased among those with very or moderately small birth weight, birth length, or head circumference for gestational age. CONCLUSIONS: During early stages of gestation, growth in length and head circumference may be more important for intellectual development than weight increase. Future studies on size at birth and intellectual performance should consider also including anthropometric measurements other than birth weight.

Adolescent↗

PubMed2005

Risk of high blood pressure among young men increases with the degree of immaturity at birth.

BACKGROUND: Survivors of preterm birth constitute a new generation of young adults, but little is known about their long-term health. We investigated the association between gestational age (GA) and risk of high blood pressure (HBP) in young Swedish men and whether GA modified the risk of HBP; ie, whether HBP was related to being born small for gestational age (SGA). METHODS AND RESULTS: This population-based cohort study included 329 495 Swedish men born in 1973 to 1981 who were conscripted for military service in 1993 to 2001. Multivariate linear- and logistic-regression analyses were performed. Main outcome measures were systolic and diastolic BPs at conscription. Linear-regression analyses showed that systolic BP increased with decreasing GA (regression coefficient -0.31 mm Hg/wk, P<0.001). Systolic and diastolic BPs both increased with decreasing birth weight for GA, but the association with systolic BP was most evident (regression coefficient -0.67 mm Hg per SD score in birth weight for GA, P<0.001). Compared with men born at term (GA, 37 to 41 weeks), the adjusted odd ratios (95% confidence intervals [CIs]) for high systolic BP (> or =140 mm Hg) were as follows: moderately preterm (33 to 36 weeks), 1.25 (1.19 to 1.30); very preterm (29 to 32 weeks), 1.48 (1.30 to 1.68); and extremely preterm (24 to 28 weeks), 1.93 (1.34 to 2.76). Being SGA was associated only with an increased risk of high systolic BP among men born at 33 weeks or later. The risk estimates for high diastolic BP (> or =90 mm Hg) increased with decreasing GA, but the risk reached significance only among men born moderately preterm. CONCLUSIONS: Preterm birth, a common pregnancy complication, is a risk factor for HBP in young men. The risk of high systolic BP associated with birth weight for GA is modified by GA, suggesting that perinatal contributions to BP elevation later in life may be induced by different biological pathways.

Adult↗

PubMed2005

Pregnancy characteristics and maternal risk of breast cancer.

CONTEXT: During pregnancy, serum levels of estrogen, progesterone, and other hormones are markedly higher than during other periods of life. Pregnancy hormones primarily are produced in the placenta, and signs of placental impairment may serve as indirect markers of hormone exposures during pregnancy. During pregnancy, these markers have been inconsistently associated with subsequent risk of breast cancer in the mother. OBJECTIVE: To examine associations between indirect markers of hormonal exposures, such as placental weight and other pregnancy characteristics, and maternal risk of developing breast cancer. DESIGN AND SETTING: Population-based cohort study using data from the Swedish Birth Register, the Swedish Cancer Register, the Swedish Cause of Death Register, and the Swedish Register of Population and Population Changes. PARTICIPANTS: Women included in the Sweden Birth Register who delivered singletons between 1982 and 1989, with complete information on date of birth and gestational age. Women were followed up until the occurrence of breast cancer, death, or end of follow-up (December 31, 2001). Cox proportional hazards models were used to estimate associations between hormone exposures and risks of breast cancer. MAIN OUTCOME MEASURE: Incidence of invasive breast cancer. RESULTS: Of 314,019 women in the cohort, 2216 (0.7%) developed breast cancer during the follow-up through 2001, of whom 2100 (95%) were diagnosed before age 50 years. Compared with women who had placentas weighing less than 500 g in 2 consecutive pregnancies, the risk of breast cancer was increased among women whose placentas weighed between 500 and 699 g in their first pregnancy and at least 700 g in their second pregnancy (or vice versa) (adjusted hazard ratio, 1.82; 95% confidence interval [CI], 1.07-3.08), and the corresponding risk was doubled among women whose placentas weighed at least 700 g in both pregnancies (adjusted hazard ratio, 2.05; 95% CI, 1.15-3.64). A high birth weight (> or =4000 g) in 2 successive births was associated with an increased risk of breast cancer before but not after adjusting for placental weight and other covariates (adjusted hazard ratio, 1.10; 95% CI, 0.76-1.59). CONCLUSIONS: Placental weight is positively associated with maternal risk of breast cancer. These results further support the hypothesis that pregnancy hormones are important modifiers of subsequent maternal breast cancer risk.

Birth Weight↗

PubMed2005

Preterm birth, low birth weight, and risk for esophageal adenocarcinoma.

BACKGROUND & AIMS: Gastroesophageal reflux is common among preterm infants and those who are small for gestational age, and it is a strong risk factor for adenocarcinoma of the esophagus. METHODS: In a cohort of 3364 individuals born preterm and/or small for gestational age between 1925 and 1949, we assessed the long-term risk for esophageal cancer. RESULTS: The standardized incidence rate ratio for esophageal adenocarcinoma was increased more than 7-fold in the cohort (standardized incidence rate ratio, 7.27; 95% confidence interval, 1.98-18.62), and a birth weight <2000 g was associated with a more than 11-fold increase in risk (standardized incidence rate ratio, 11.5; 95% confidence interval, 1.39-41.5). CONCLUSIONS: The associations may be spurious, but if not, they may be explained by increased gastroesophageal reflux during infancy among infants born preterm and/or small for gestational age.

Adenocarcinoma↗

PubMed2005

Does prenatal sonography affect intellectual performance?

BACKGROUND: Little is known about potential risks of ultrasound during pregnancy. The developing brain is susceptible to environmental influences, and prenatal ultrasound has been reported to affect cognitive abilities in animals. METHODS: To assess a possible association between prenatal ultrasound and intellectual performance, we studied men born in Sweden from 1973 to 1978 who enrolled for military service from 1991 to 1996. Intellectual scores (mean +/- standard deviation = 5 +/- 2) were measured by a test battery at enrollment, and subnormal performance was defined as a score of 3 or less. We estimated differences in mean intellectual score between ultrasound-exposed and ultrasound-unexposed using linear regression, and we calculated relative risks of subnormal performance using logistic regression analysis. RESULTS: There were 7999 eligible men born in a hospital (Malmo) that included ultrasound scanning in standard antenatal care (exposed) and 197,829 men born in hospitals without ultrasound scanning programs (unexposed). We found lower intellectual performance scores (mean difference = -0.16; 95% confidence interval = -0.21 to -0.11) and an increased risk of subnormal performance (odds ratio = 1.28; CI = 1.18 to 1.38) among ultrasound-exposed compared with unexposed. However, men born in Malmo before scanning was introduced also had lower scores, and the decrease in test scores after the introduction of ultrasound was small. Moreover, we found no differences in intellectual performance within pairs of brothers as a result of ultrasound exposure. CONCLUSIONS: This study failed to demonstrate a clear association between ultrasound scanning and intellectual performance.

Adolescent↗

PubMed2005

Birth characteristics and risk of high systolic blood pressure in early adulthood: socioeconomic factors and familial effects.

BACKGROUND: Although an inverse association between size at birth and blood pressure has been found in several studies, few studies have adjusted for the influence of socioeconomic and familial effects. METHODS: We investigated whether the association between birth weight and systolic blood pressure in young men is confounded by socioeconomic factors in adolescence or familial factors (ie, common genes and shared environment). Our population-based cohort study comprised 330,768 Swedish men born between 1973 and 1981, and conscripted for military service between 1991 and 2000. The analyses of family effects were restricted to 89,856 siblings from the initial cohort. A high systolic blood pressure at conscription was defined as a systolic blood pressure >/=140 mm Hg. Birth weight for gestational age <-2 standard deviation scores was considered "light for gestational age." RESULTS: Compared with men who had normal birth weight for gestational age, men who had been born light for gestational age were at increased risk of high systolic blood pressure (odds ratio = 1.14; 95% confidence interval = 1.07-1.22), even after adjustment for important confounders such as socioeconomic status. The increase in risk of high systolic blood pressure related to 1 standard deviation score decrease in birth weight for gestational age was similar within families (1.08; 1.04-1.12) and between families (1.05; 1.03-1.08). CONCLUSIONS: This study suggests that low birth weight for gestational age slightly increases the risk of high systolic blood pressure, and that the association appears not to be confounded by socioeconomic or familial effects.

Adult↗

PubMed2005

Maternal smoking and causes of very preterm birth.

BACKGROUND: Smoking increases the risk of preterm birth. The present study was made to elucidate the relation of smoking to causes of very preterm birth. METHODS: In a case-control study on all very preterm births in two regions of Stockholm 1988-1992, prospectively collected data were extracted from antenatal and delivery records on smoking, other maternal characteristics, pregnancy complications, and causes of preterm birth. Cases were live single births with a gestational age of < or =32 weeks and 0 days, and controls were live singletons delivered at 37 weeks or later (n = 295, respectively). Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated with logistic regression. RESULTS: Compared with non-smokers, adjusted ORs of very preterm birth among moderate smokers (1-9 cigarettes per day) and heavy smokers (> or =10 cigarettes per day) were 1.4 (95% CI 0.8-2.4) and 2.9 (95% CI 1.5-5.7), respectively. Compared with non-smokers, risk of preterm labor was increased among moderate and heavy smokers [ORs 1.9 (95% CI 1.0-3.6) and 2.6 (95% CI 1.1-1.6), respectively]. These risks remained essentially unchanged in women without an identifiable cause of preterm labor ('idiopathic preterm labor'). Smoking was also associated with dose-dependent increases in risks of preterm birth due to preterm premature rupture of membranes and late pregnancy bleedings. There was no association between smoking and risk of very preterm birth caused by hypertensive diseases. CONCLUSIONS: Smoking increases the risk of very preterm birth caused by preterm labor (including idiopathic preterm labor), preterm premature rupture of membranes, and late pregnancy bleedings.

Adult↗