Risk factors for procedure-related fetal losses after mid-trimester genetic amniocentesis

The objective of this study was to determine the institutional pregnancy loss rate following second-trimester genetic amniocentesis and to ascertain whether factors exist which would identify pregnancies at increased risk of having a procedure-related fetal loss.

University Teaching Hospital

Details of the procedure and pregnancy outcome of all patients who had amniocentesis planned or performed between 15-22 gestational weeks between January 1997 and June 2004 were extracted from our clinical audit database. The procedure-related fetal loss rate, defined as all unintended abortions, stillbirths and neonatal deaths without major fetal abnormalities or obvious obstetric causes, was determined and compared to a presumed background fetal loss rate of 0.8% based on a cohort of women who did not undergo the procedure.

A total of 3468 consecutive amniocentesis were performed in 3440 patients with 3498 fetuses. The mean gestational age at amniocentesis was 17.6 +/- 1.2 weeks. The majority (98.6%) required only one puncture and a transplacental procedure was required in 2.7% cases. A total of 3465 chromosomal studies were performed. Sixty six cases (1.9%) of major chromosomal abnormalities were detected. Pregnancy outcome was ascertained in all except 26 singleton pregnancies (0.74%). There were 3285 (93.9%) livebirths, 103 (2.9%) termination of pregnancies (TOP), 6 (0.17%) fetal demises before the procedure, and 20 (0.61%) unintended fetal losses due to significant fetal abnormalities or obstetric complications. The remaining 58 fetal losses (1.66%) were classified as potentially procedure-related, which could be either background fetal losses or procedure-related. The procedure-related fetal loss rate after correcting for the background loss rate was 0.86%.Potentially procedure-related fetal losses were found to be significantly associated with a procedure at 18 weeks or beyond (odds ratio OR = 1.97), a procedure performed for abnormal second-trimester biochemical screening test (OR = 3.08), a bloody tap (OR = 6.48), and a female fetus (OR = 2.39); but not to the number of punctures (p = 0.66) nor transplacental amniocentesis (p = 0.104).

Mid-trimester amniocentesis is associated with a small but significant risk of fetal loss of 0.86%.