Effects of smoking during pregnancy: Five meta-analyses

Background: The purpose of this study was to estimate, using meta-analysis, pooled odds ratios for the effects of smoking on five pregnancy complications: placenta previa, abruptio placenta, ectopic pregnancy, preterm premature rupture of the membrane (PPROM), and pre-eclampsia. Methods: Published articles were identified through computer search and literature review. Five criteria were applied to those studies initially identified to determine those eligible for the meta-analysis. A random effects model was applied to derive pooled odds ratios for the eligible studies for each pregnancy complication. Meta-analyses were repeated on subsets of the studies to confirm the overall results. Results: Smoking was found to be strongly associated with an elevated risk of placenta previa, abruptio placenta, ectopic pregnancy, and PPROM, and a decreased risk of pre-eclampsia. All pooled odds ratios were statistically significant. The pooled ratios ranged from 1.58 for placenta previa to 1.77 for ectopic pregnancy. The pooled odds ratio for pre-eclampsia was 0.51 and all subset analyses confirmed this seemingly protective effect. Conclusions: Smoking during pregnancy is a significant and preventable factor affecting ectopic pregnancy, placental abruption, placenta previa, and PPROM. The findings of smoking’s apparently protective effect on pre-eclampsia should be balanced with these harmful effects. In addition, the biological linkage between smoking and pre-eclampsia is not yet well understood. Pregnant women should be advised to stop smoking in order to reduce the overall risk of pregnancy complications as well as any risk of adverse impact on the unborn child.