Early amniocentesis versus transabdominal chorion villus sampling for prenatal diagnosis.

BACKGROUND

A major disadvantage of amniocentesis is that test results are usually available only after 18 weeks gestation. Early amniocentesis can now be done between 9 to 14 weeks gestation.

OBJECTIVES

The objective was to assess the safety and accuracy of early amniocentesis compared with chorion villus sampling.

SEARCH STRATEGY

The Cochrane Pregnancy and Childbirth Group trials register and the Cochrane Controlled Trials Register were searched. Date of last search: October 1998.

SELECTION CRITERIA

Randomised trials comparing early amniocentesis with transabdominal chorion villus sampling.

DATA COLLECTION AND ANALYSIS

One reviewer assessed eligibility and trial quality.

MAIN RESULTS

Three studies were included. Sampling failure was 0.4% in the early amniocentesis group compared to 2% in the chorion villus group (relative risk 0.23, 95% confidence interval 0.08 to 0.65). Consequently, more women in the chorion villus sampling group needed a second prenatal diagnostic test (relative risk 0.43, 95% confidence interval 0.21 to 0.88). There were no statistically significant differences in the laboratory failures (relative risk 0.43, 95% confidence interval 0. 17 to 1.10) or number of women with various chromosomal abnormalities (relative risk 0.51, 95% confidence interval 0.26 to 1. 04). Combined total pregnancy loss in the early amniocentesis group was 6.2% (57/915) compared with 5% (46/917) in the chorion villus sampling group (relative risk 1.24, 95% confidence interval 0.85 to 1.81). There were more spontaneous miscarriages after early amniocentesis (4.4% versus 2.3%, relative risk 1.92, 95% confidence interval 1.14 to 3.23). There was no difference in the incidence of neonatal respiratory distress and anomalies in the newborn infants. The incidence of talipes was greater in the early amniocentesis group, although haemangiomas were more common in the chorion villus sampling group.

REVIEWER'S CONCLUSIONS: Current data suggest that early amniocentesis is associated with a greater risk of spontaneous miscarriage and neonatal talipes compared to transabdominal chorion villus sampling. An increased risk of these complications needs to be weighed against fewer technical difficulties and the possibility of fewer neonatal haemangiomas.