A Cochrane review [Abstract] 1 included 14 studies. In a low risk population with a background pregnancy loss of around 2%, a second trimester amniocentesis will increase this risk by another 1%..Spontaneous miscarriages are more common following second trimester amniocentesis as compared with controls with no amniocentesis (2.1% vs. 1.3%; RR 1.02-2.52). Early amniocentesis is not a safe early alternative to second trimester amniocentesis because of increased pregnancy loss (7.6% vs. 5.9%; RR 1.29, 95% CI 1.03 to 1.61) and higher incidence of talipes compared to CVS (chorionic villus sampling) (RR 6.43, 95% CI 1.68 to 24.64). Compared with second trimester amniocentesis, transcervical CVS carries a significantly higher risk of pregnancy loss (14.5% versus 11%; RR 1.40, 95% CI 1.09 to 1.81) and spontaneous miscarriage (12.9% versus 9.4%; RR 1.50, 95% CI 1.07 to 2.11). One study compared transabdominal CVS with second trimester amniocentesis and found no significant difference in the total pregnancy loss between the two procedures (6.3% versus 7%). Transcervical CVS is more technically demanding than transabdominal CVS with more failures to obtain sample and more multiple insertions.
A retrospective study 2 evaluated procedures of invasive prenatal testing (2001-2014) including 936 amniocentesis procedures and 1051 chorionic villus samplings, of which 405 cases were executed transabdominally and 646 transcervically. Only singleton pregnancies before 24 weeks and 0 days of gestation where the pregnancy outcome was known were included. The total fetal loss rates were determined to be 1.73% for transabdominal chorionic villus sampling, 2.01% for transcervical chorionic villus sampling and 1.18% for amniocentesis. No statistically noticeable differences between the total fetal loss rates of all three procedures were found (P=0.399).
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