Individual risk of fetal loss following routine second trimester amniocentesis: a controlled study of 20,460 cases.

PURPOSE: The aim of this study was to evaluate the impact of maternal risk factors on excess fetal loss related to amniocentesis. MATERIALS AND METHODS: We compared fetal outcome and details of risk factors for fetal loss in 20,460 patients undergoing amniocenteses between April 1997 and March 2005 to 11,017 controls given ultrasound during the same period in our tertiary level prenatal unit. The risk factors were recorded before the procedure. Spontaneous fetal loss was defined as spontaneous miscarriage and intrauterine fetal demise at any gestational age. RESULTS: The excess rate of spontaneous loss attributed to the amniocentesis procedure averaged 0.49 % (CI: 0.26 - 0.72) for all pregnancies under routine care (1.31 % 268/20,460 versus 0.82 % 90/11,017). The fetal loss rate was increased in the intervention group for the following isolated risk factors: vaginal bleeding before procedure (19/647, 2.9 % CI: 1.6 - 4.2 %); vaginal bleeding at date of procedure (3/33, 9.1 % CI: - 0.7 - 18.9 %); a history of 3 or more spontaneous abortions (6/257, 2.3 % CI: 0.5 - 4.2 %); body mass index > 40 (5/160, 3.1 % CI: 0.4 - 5.8 %) and cigarette consumption > 10/day (13/671, 1.94 % CI: 0.9 - 3.0). If none of these risk factors was present, the abortion rate in the intervention group was 1.18 % (219/18,617) and 0.63 % (61/9,677) in the control group. Maternal age > 40 at birth did not alter the rate of loss in the intervention group, but did in the control group (1.4 % 38/2,717 and 1.69 % 7/414). CONCLUSION: After routine amniocentesis patients have an additional procedure-related risk of spontaneous pregnancy loss equivalent to 0.5 %. The absence of risk factors in the patient's history does not reduce this additional risk.