First-Trimester Vaginal Bleeding and Complications Later in Pregnancy

Abstract

First-trimester vaginal bleeding is a common complication of pregnancy with an incidence of 15% to 25%. Approximately 50% of pregnant women with such bleeding miscarry before 20 weeks' gestation, and those who do not seem to be at increased risk of other complications later in pregnancy. Several studies have investigated the association between first-trimester bleeding and the risk of complications later in the same pregnancy but have not studied the consequences of such bleeding in a second pregnancy. This registry-based, retrospective cohort study investigated the association between first-trimester bleeding and later complications in both the first and second pregnancies. Data were obtained from the National Patient Registry on all first (n = 782,287) and second pregnancies (n = 536,419) delivered between 1978 and 2007. First-trimester bleeding was defined as vaginal bleeding diagnosed before 12 completed weeks' gestation. Multivariate logistic regression analysis was used to calculate the associations across the two pregnancies and to adjust for maternal age and calendar year. First-trimester bleeding increased the risk of delivering preterm in weeks 32 to 36 from 3.6% to 6.1% (adjusted odds ratio [aOR], 1.65; 95% confidence interval [CI], 1.57-1.77) and in weeks 28 to 31 from 0.3% to 0.9% (aOR, 2.98; 95% CI, 2.50-3.54). First-trimester bleeding was also associated with an increased risk of placental abruption (aOR = 1.48; 95% CI: 1.30-1.68). In addition, first-trimester bleeding in the first pregnancy increased the risk of recurrence in the second pregnancy from 2.2% to 8.2% (aOR, 4.05; 95% CI, 3.78-4.34), of preterm delivery from 2.7% to 4.8% (aOR, 1.83; 95% CI, 1.67-2.00), and of placental abruption from 0.9% to 1.0% (aOR, 1.29; 95% CI, 1.07-1.56). These findings suggest that first-trimester vaginal bleeding in a first pregnancy may be a clinically relevant marker for recurrence of first-trimester bleeding in a subsequent pregnancy and for increased risk of later complications in both the first and second pregnancy.