Risk factors predisposing to fetal loss following a second trimester amniocentesis

To examine the influence of possible risk factors on fetal loss rate following amniocentesis.

Retrospective analysis of case records between 1993 and 1998.

Fetal medicine unit of a large teaching hospital.

One thousand and six women with singleton pregnancies formed the study group. Seven hundred and eight of them had bleeding during the current pregnancy before the procedure. while 298 had a history of three or more first trimester abortions and/or a second trimester miscarriage or termination of pregnancy. Four thousand and twenty-four women who had amniocentesis and had no risk factors served as controls. Both groups were also classified according to maternal age. Group 1:1,610 women aged 20-34 years; Group 2: 2850 women aged 35-39 years; Group 3; 570 women > 40 years.

Women of both groups underwent a second trimester amniocentesis between 16 and 21 weeks of gestation. Fetal losses following amniocentesis were examined in three time intervals: 1. in the first two weeks after the procedure; 2. up to the 28th week; 3. from the 28th week to term.

There was a statistically significant difference in the fetal loss rate between women aged 20-34 years (2.54%) and those > 40 years (5.1%). Women with a history of vaginal bleeding during the current pregnancy had a higher fetal loss rate compared with controls (6.5% vs 2.8%), which corresponds to an odds ratio of 2.4 (95% CI 1.69-3.42). A similar difference was found between the group of women with a history of previous abortions/terminations and the controls (8% vs 2.8%): OR 3.03 (95% Cl 1.92-4.79).

There is a higher risk of fetal loss following amniocentesis in women > 40 years of age compared with those aged 20-34 years. Bleeding in the current pregnancy, a history of three or more first trimester abortions, a second trimester miscarriage or termination of pregnancy seem to be significant predisposing factors for fetal loss after an amniocentesis.