Objective: To analyze the effect of passive smoking of pregnancy women in early pregnancy and different stages during pregnancy on fetal Low-Birth-Weight.
Methods: Meta analysis was applied to analyze the relationship between maternal passive smoking during pregnancy and fetal low-birth-weight. NCBI, OVID-MEDLINE, CNKI, VIP and CBM were searched with the language limited to Chinese and English. The search was finished in April 2008. Pooled ORs with 95% CI were estimated.
Results: Totally, 26 papers were got, including 20 cohort studies and 6 case-control studies. Maternal passive smoking was associated with an increased risk of low-birth-weight. The unadjusted pooled OR was 1.65 (95% CI = 1.39-1.97), and the adjusted pooled OR was 1.60 (95% Ci = 1.25 - 2.05). The pooled OR of exposure with lowest and highest level were OR = 1.53 (95% CI: 1.14 - 2.04)and OR = 2.53(95% CI: 1.46-4.36), respectively. The pooled OR of exposure at early pregnancy was 1.12 (95% CI = 0.82-1.55), with no statistically significance.
Conclusion: Maternal passive smoking during pregnancy could increase the risk of delivering a low birth-weight baby. Middle or late pregnancy might be the sensitive period of passive smoking's effect. Whether passive smoking' s threshold effect exists or not is still not sure.