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.

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.

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.

Plasma folate levels and risk of spontaneous abortion.

CONTEXT: Both folate deficiency and folic acid supplements have been reported to increase the risk of spontaneous abortion. The results are inconclusive, however, and measurements of folate have not been available in all studies. OBJECTIVE: To study the association between plasma folate levels and the risk of spontaneous abortion. DESIGN, SETTING, AND POPULATION: Population-based, matched, case-control study of case women with spontaneous abortion and control women from January 1996 through December 1998 in Uppsala County, Sweden. Plasma folate measurements were available for 468 cases and 921 controls at 6 to 12 gestational weeks. MAIN OUTCOME MEASURE: Risk of spontaneous abortion vs maternal plasma folate level. RESULTS: Compared with women with plasma folate levels between 2.20 and 3.95 ng/mL (5.0 and 8.9 nmol/L), women with low (< or =2.19 ng/mL [< or =4.9 nmol/L]) folate levels were at increased risk of spontaneous abortion (adjusted odds ratio [OR], 1.47; 95% confidence interval [CI], 1.01-2.14), whereas women with higher folate levels (3.96-6.16 ng/mL [9.0-13.9 nmol/L] and > or =6.17 ng/mL [> or =14.0 nmol/L]) showed no increased risk of spontaneous abortion (OR, 0.84; 95% CI, 0.59-1.20; and OR, 0.74; 95% CI, 0.47-1.16, respectively). Low folate levels were associated with a significantly increased risk when the fetal karyotype was abnormal (OR, 1.95; 95% CI, 1.09-3.48) but not when the fetal karyotype was normal (OR, 1.11; 95% CI, 0.55-2.24) or unknown (OR, 1.45; 95% CI, 0.90-2.33). CONCLUSION: Low plasma folate levels were associated with an increased risk of early spontaneous abortion.