Background. Most published reports on early amniocentesis are of cohort studies rather than randomised trials. This study was designed to assess the safety and cytogenetic accuracy of early amniocentesis in contrast to midtrimester amniocentesis in a randomised multicentre setting. Methods. Pregnant women were randomly allocated early amniocentesis (between 11+0 and 12+6 gestational weeks(days)) or midtrimester (between 15+0 and 16+6 gestational weeks(days)) amniocentesis. A detailed fetal ultrasound examination was done between 15 and 20 gestational weeks in all women. All amniocenteses were done under continuous ultrasound guidance: 11 mL (early amniocentesis) or 20 mL (midtrimester amniocentesis) of amniotic fluid were removed for cytogenic analysis. No more than two needle insertions were done on the same day. All fetal losses (spontaneous or induced abortions) were counted as outcome events and post-procedural losses had cytogenic analysis. Maternal and fetal health were assessed at 20-22 weeks and 5 weeks after delivery. Logistic regression analysis was used to assess the significance of the differences between the early amniocentesis and midtrimester amniocentesis groups. Findings. 4374 pregnant women took part in the study. 1916 (87.8%) of 2183 women in the early amniocentesis group had their amniocentesis before 13 gestational weeks. 1775 (81.2%) of 2185 women in the midtrimester group had their amniocentesis after 15 gestational weeks. There was a significant difference in total fetal losses for early amniocentesis compared with midtrimester amniocentesis (7.6% vs 5.9%; difference 1.7%, one-sided CI 2.98%, p = 0.012). There was a significant increase in talipes equinovarus in the early amniocentesis group compared with the midtrimester amniocentesis group (1.3% vs 0.1%, p = 0.0001). There was a significant difference in postprocedural amniotic-fluid leakage (early amniocentesis 3.5% vs midtrimester amniocentesis 1.7%, p = 0.0007). Interpretation. Our study shows that early amniocentesis is associated with an increased risk of fetal loss and talipes equinovarus. Our results should be taken into consideration when invasive prenatal diagnosis is being offered.
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