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Early Amnio Increases Risk for Clubfoot and Pregnancy Loss

Amnio at 13 weeks' gestation increased risk in this cytogenically normal cohort.

Amniocentesis at 15 weeks' gestation has become increasingly safe, and there are reasons to investigate whether the procedure could be performed at even earlier gestational ages. First, chorionic villus sampling (CVS), traditionally performed at 10 to 12 weeks' gestation, might not be available. And second, with increasing use of first-trimester noninvasive prenatal screening (measurement of nuchal translucency and maternal serum analytes), more women with abnormal screening results require definitive evaluation. However, several large collaborative studies have shown unacceptably high pregnancy loss rates when amniocentesis is performed before 15 weeks' gestation.

This study, funded by the National Institute of Child Health and Human Development, involved 3775 women seeking invasive screening procedures because of advanced maternal age, previous fetal trisomy, or positive noninvasive screening results. The women were randomized to undergo either transabdominal CVS or amniocentesis between 11 and 14 weeks' gestation (i.e., the time frame relevant for follow-up of noninvasive first-trimester screening). Before and during recruitment, other studies showed unacceptably high complication rates for amniocentesis performed at 11 and 12 weeks' gestation. Therefore, the earlier study arms were dropped, and more than 90% of procedures were performed during weeks 13 and 14.

Almost all women underwent their assigned procedures and were followed through delivery; analyses were restricted to the cytogenetically normal cohort (n=3698). The combined outcome of spontaneous loss before 20 weeks and procedure-related termination occurred slightly more often after amniocentesis than after CVS, with risk most increased when amniocentesis was performed during week 13 (relative risk, 2.07; P=0.05). In addition, incidence of talipes equinovarus (clubfoot) was fourfold higher after amniocentesis than after CVS (P=0.02); again, most cases occurred when amniocentesis was performed during week 13 (RR, 4.65).

Comment: Amniocentesis at 13 weeks' gestation is clearly associated with increased risk for talipes equinovarus and probably associated with increased risk for pregnancy loss, compared with amniocentesis at 15 weeks. The presumptive mechanism is amniotic-fluid leakage after the procedure. Early amniocentesis should not be part of the accepted prenatal diagnostic regimen. Definitive testing should be accomplished by chorionic villus sampling or by amniocentesis at 15 weeks or later.

— Sandra Ann Carson, MD

Published in Journal Watch Women's Health July 20, 2004

Citation(s):

Philip J et al. Late first-trimester invasive prenatal diagnosis: Results of an international randomized trial. Obstet Gynecol 2004 Jun; 103:1164-73.

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