Objectives: The aim of this study is to determine the complications of third trimester amniocentesis for fetal karyotyping among women unwilling to accept the fetal loss risks of second trimester amniocentesis.
Materials and methods: A retrospective study was carried out from January 1998 to December 2006 of 182 singleton pregnancies that underwent a late amniocentesis (after 32 weeks) for fetal karyotyping. The indications were integrated risk (maternal age, first trimester nuchal translucency, second trimester maternal serum markers) over 1/250 (n=68), isolated maternal age over 38 years (n=51), isolated abnormal second trimester biochemical markers (n=34), history of personal or familial a chromosomal abnormality (n=21) or maternal choice (n=8). Presence of fetal abnormalities at ultrasound or context of viral or parasitologic seroconversion as well as multiple pregnancies were considered as non-inclusion criteria.
Results: Median maternal age and gestational age at sampling were 39 years (range 23-48) and 32.4 weeks (29.5-37.6). Median interval between amniocentesis and definitive results of amniocentesis on the one hand, and delivery on the on the hand were 15 days (7-42) and 47 days (8-69), respectively. There were no chromosomal abnormality and non-termination of pregnancy. Nine patients out of 182(5%) had a spontaneous labour followed by premature delivery before 37 weeks and six women (3.3%) among those nine displayed preterm premature rupture of membranes (PPROM). Four patients out of 182 (2%) gave birth before definitive karyotyping result but all of them had a direct fluorescence in situ hybridisation analysis with a normal karyotyping result known well before delivery.
Conclusions: The risk of preterm premature rupture of membrane is 3.3%, with a 5% risk of premature delivery before 37 weeks. This late procedure provides a safe reassurance to women who are unwilling to accept the risks of earlier amniocentesis. However, it should only be used in particular situation and in countries were legislation allows late termination of pregnancy.