Research ArticlesEffects of smoking during pregnancy: Five meta-analyses
Introduction
Despite widespread evidence that smoking during pregnancy adversely impacts the health of the newborn, a self-reported 19% of American women continue to smoke during pregnancy.1 The true prevalence of tobacco use by pregnant women may be even higher: Studies that biochemically validate tobacco exposure suggest that pregnant women may either fail to disclose or underreport their use of tobacco during pregnancy.2, 3 The risks associated with this behavior are well documented. The literature provides examples of numerous studies that link tobacco use during pregnancy to an increased risk of low birthweight, perinatal mortality, and sudden infant death syndrome (SIDS).4, 5 Moreover, the impact of smoking during pregnancy may occur well before the birth of the child: Research indicates that use of tobacco can affect a woman’s ability to carry a pregnancy to term without complications.
Full information on the extent of smoking’s risk to the newborn and the pregnant mother is vital for motivating physician efforts to encourage women of reproductive age to quit smoking. Unfortunately, much of the research on the impact of tobacco use on the health of the pregnancy itself has been published piecemeal, failing to provide physicians with an overall view of the risks posed by smoking to the mother. Methodologic limitations within some studies in this area may additionally undermine the use of such research by health care practitioners. For example, a number of studies evaluating the impact of smoking on pregnancy complications have failed to control for additional factors believed to be associated with the event. Examples include research on ectopic pregnancy not adjusting for a history of pelvic inflammatory disease6, 7, 8; research on placenta previa and placental abruption not controlling for parity9, 10; and research on pre-eclampsia not adjusting for body mass index.11 Failure to adjust for potential confounders may lead to variation in effect sizes from study to study and devalue the results on effect size for use by health care practitioners.
In an effort to substantiate and summarize research on the association between smoking during pregnancy and the risk of major maternal pregnancy complications, we undertook meta-analyses on the association between smoking and five adverse pregnancy events. Using meta-analyses, we derived summary measures (odds ratio) of the association of cigarette smoking during pregnancy with abruptio placenta, placenta previa, ectopic pregnancy, pre-eclampsia, and preterm premature rupture of the membrane (PPROM). Meta-analysis is a statistical method that allows researchers to combine data from different studies on the same topic. This method increases the statistical power beyond that of individual studies and can provide robust and unbiased summary measures of association. In incorporating summary measures of effect for all major pregnancy complications found to have an association with smoking within one paper, we are able to present a comprehensive picture of the risks that smoking poses to a pregnancy.
Section snippets
Study selection
Using the MEDLINE and Current Contents databases for 1966 through May 1995, we searched for published research examining the association between smoking during pregnancy and pregnancy complications. We retrieved all relevant publications, including review articles, and examined their bibliographies for additional references on the topics. We included only English-language North American or Western European studies because we assumed that these populations would be more homogeneous in their
Results
The 34 studies used in the meta-analyses, their study design, and their determined odds ratios are listed in Table 1A, Table 1B, Table 1C, Table 1D, Table 1E. The pooled odds ratios and 95% confidence intervals for each pregnancy complication are presented in Table 2. We note that the CIs presented here are larger than they would be if we had used the fixed effects model and reflect variation due to possible heterogeneity among studies.
Preterm premature rupture of the membranes (PPROM)
Simple PROM is the premature rupture of the (amniotic) membranes before spontaneous onset of labor. With expectant management of PROM, 9 of 10 patients will progress into labor. More troublesome is preterm PROM, or PPROM, which is PROM that occurs before 37 weeks of gestation. In the United States, PPROM occurs in 0.7% to 2.0% of pregnancies34 and approximately 30% of preterm births.35 The measure of effect derived in the meta-analysis for this condition was an odds ratio of 1.70 (95% CI = 1.18
Discussion
Our meta-analyses showed that cigarette smoking during pregnancy is strongly associated with an elevated risk for abruptio placenta, ectopic pregnancy, and PPROM, and a decreased risk for pre-eclampsia. Although the overall placenta previa meta-analysis also showed a significant association between smoking during pregnancy and previa, none of the previa “subset” analyses (those that analyzed subsets of studies defined by certain study design characteristics)resulted in statistically significant
References (48)
- et al.
Cigarette smoking during pregnancy in relation to placenta previa
Am J Obstet Gynecol
(1991) - et al.
The relationship between exposure during pregnancy to cigarette smoking and cocaine use and placenta previa
Am J Obstet Gynecol
(1994) - et al.
Relationship of maternal smoking during pregnancy to placenta previa
Am J Prev Med
(1992) - et al.
Risk factors for preterm premature rupture of fetal membranesa multicenter case-control study
Am J Obstet Gynecol
(1990) - et al.
Epidemiological correlates of preterm premature rupture of membranes
Int J Gynecol Obstet
(1994) - et al.
Risk factors for preeclampsia in healthy nulliparous womena prospective multicenter study
Am J Obstet Gynecol
(1995) - US Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention. Advance...
- et al.
Integrating smoking cessation into routine public prenatal carethe Smoking Cessation Pregnancy Project
Am J Public Health
(1995) - et al.
Health education for pregnant smokersits behavioral impact and cost benefit
Am J Public Health
(1993) - et al.
Effect of maternal cigarette smoking on pregnancy complications and sudden infant death syndrome
Fam Prac
(1995)
The relationship of smoking and ectopic pregnancy
Am J Public Health
Induced abortions, contraceptive practices and tobacco smoking as risk factors for ectopic pregnancy in Athens
Br J Obstet Gynecol
Maternal cigarette smoking and the risk of tubal pregnancy
Am J Epidemiol
The effect of placenta previa on blood loss in second-trimester pregnancy termination
Obstet Gynecol
Factors associated with abruptio placentae in preterm deliveries
Acta Obstet Gynecol Scan
Cigarette smoking and pre-eclampsia
Obstet Gynecol
Meta-analysis in clinical trials
Cont Clin Trials
Maternal smoking and placenta previa
Epidemiology
Smoking and drinking during pregnancytheir effects on preterm birth
JAMA
Bleeding during the latter half of pregnancy
Correlates of placental abruption
Br J Obstet Gynaecol
Risk factors for abruptio placentae
S Afr Med J
Placental abruption in the preterm gestationan association with chorioamnionitis
Obstet Gynecol
Cited by (351)
The environmental risk factors associated with ectopic pregnancy: An umbrella review
2023, Journal of Gynecology Obstetrics and Human ReproductionCitation Excerpt :In total, six meta-analyses were included that were eligible for inclusion in this umbrella review (Figure 1). These six eligible articles [13–17] included nine meta-analyses with 55,755 EP cases with 860,623 subjects. Meta-analyses were based on cohort, cross-sectional or case-control design.
Airway pollution and smoking in reproductive health
2022, Best Practice and Research: Clinical Obstetrics and GynaecologyCigarette smoke-induced trophoblast cell ferroptosis in rat placenta and the effects of L-arginine intervention
2022, Ecotoxicology and Environmental Safety