Background: To evaluate the impact of surgically induced first-trimester abortion on the risk of miscarriage in a subsequent pregnancy.
Methods: The study is a pregnancy cohort study. It was conducted among 15 general hospitals or maternity and infant health institutes in Shanghai, China from November 1993 to March 1998. The abortion cohort consisted of pregnant women whose previous pregnancies were terminated by vacuum aspiration (98%). The reference cohort consisted of primigravidae. Subjects were recruited at 35-63 days of gestational age. A total of 2953 pregnant women were enrolled; 1502 in the abortion cohort, 1451 in the reference cohort.
Results: There were only 62 women lost to follow-up. The remaining 2891 women had 2732 live births, and 137 miscarriages. About 5.5% of pregnancies in the abortion cohort were miscarried and 4.0% in the reference cohort. Once potential confounders were controlled for by logistic regression, odds ratio (OR) of miscarriage between the abortion cohort and the reference cohort was 1.55 (95% CI: 1.08-2.23). The adjusted OR were 2.44 (95% CI: 1.16-5.15) among women who were recruited within 49 days of gestational age, and 1.72 (95% CI: 1.09-2.72) for the first-trimester miscarriage.
Conclusions: Induced abortion by vacuum aspiration is associated with an increased risk of first-trimester miscarriage in the subsequent pregnancy.