Amniocentesis in twin gestation: the association between gestational age at procedure and complications.

Purpose: Third trimester amniocentesis is often performed when indications arise after 24 weeks of gestation-typically to investigate new sonographic findings, and might be related to pre-term birth. Scarcity of data exists concerning the risks of third-trimester amniocentesis in twin pregnancies.

Methods: A retrospective cohort study of all twin gestations that underwent amniocentesis in a tertiary hospital between 2007 and 2016. Outcomes and procedure-related complications were compared between third-trimester (≥ 24 weeks) and mid-trimester amniocentesis (16-23 weeks). Primary outcome was defined as membrane rupture within four weeks of procedure. Logistic regression analysis was utilized to adjust results to potential confounders.

Results: Overall, 185 eligible women were included, of them, 28 (15.1%) underwent third-trimester amniocentesis and 157 (84.9%) underwent mid-trimester amniocentesis. Women in the third-trimester amniocentesis group were younger and presented higher frequencies of intra-uterine growth restriction (31.5 vs. 35.3, p < 0.001, and 28% vs. 10% p = 0.015, respectively). The prevalence of membrane rupture within 4 weeks of the procedure was significantly higher in the third-trimester amniocentesis group (31% vs. 1%, p < 0.001). Delivery rates after third-trimester amniocentesis within 1, 2 and 4 weeks of the procedure were 11%, 14.8% and 52%, respectively, versus 0% following mid-trimester amniocentesis (p < 0.001). Gestational age at delivery was similar between the groups (35.7 vs. 36.4 gestational weeks, p = 0.34). In multivariate analysis, gestational age at amniocentesis was found to be an independent risk factor for premature rupture of membranes within 4 weeks of the procedure.

Conclusion: Third trimester amniocentesis in twin pregnancies is associated with significantly higher rates of procedure-related membrane rupture compared to mid-trimester amniocentesis.