Study on the correlation between vaginal bleeding in first trimester and preterm birth: A birth cohort study in Lanzhou, China

Objects To investigate the correlation between first trimester vaginal bleeding and preterm birth (PB), and to offer suggestions on the perinatal health care and preterm birth prevention. Methods A birth cohort study was conducted on 10 179 pregnant women. Unconditional logistic regression model was used to evaluate the associations between vaginal bleeding and preterm birth in sub-preterm groups. Results Of the 10 179 pregnant women included, a total of 1001 women suffered from vaginal bleeding during the first trimester, of which 119 suffered from PB. Any vaginal bleeding increased the risk of PB. Severe bleeding was a high-risk factor of PB, associated with 4.8-fold risk of very PB, 2.7-fold risk of spontaneous PB without PROM (premature rupture of membrane) and 4.6-fold risk of medical induced PB. Bleeding prolonged more than 1 week increased 66% risk of PB and 36% risk of PB on initial episode happened in 5-12 weeks of gestation age, especially in moderate PB, in medical-induced PB and in spontaneous PB with PPROM (preterm premature rupture of membrane which is one cause of PB). Mild bleeding or bleeding within 1 week or initial episode happened within 4 weeks of gestation age possibly had no influence on PB. Conclusion Vaginal bleeding in the first-trimester was an independent risk factor for PB. The severity, duration and initial time of vaginal bleeding had different effects on different subtypes of PB.