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Prenat Diagn. 2006 Oct;26(10):925-30.

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

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Fetal Medicine Unit, Department of Obstetrics and Gynaecology, Prince of Wales Hospital, The Chinese University of Hong Kong Shatin, Hong Kong SAR, China.



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%.

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