OP05.05: Counselling patients with positive non‐invasive prenatal screens: how maternal age and ultrasound findings impact positive predictive values

Abstract

Conclusions: This study shows that gestational age has a significant effect on the accuracy of fetal gender determination ultrasound in the first trimester. Identification male 11 weeks (CRL <57 mm) is difficult and prone to a high rate of errors. OP05.04Non-invasive diagnosis of RhD status and fetal gender from maternal plasma: our results from years 2008 to 2014Objectives: The aim of the study was to perform non-invasive prenatal detection of fetal RhD gene (RHD) from plasma of RhD-negative pregnant women to detect RhD materno-fetal incompatibility together with fetal sex. Methods: We tested 354 plasma samples of RhD negative mothers (range 10-38 wks). In the first pilot phase (2008-2012) 281 samples were tested for RHD exon 10 only. In the second phase (2012-2014) 73 samples were tested for three RHD exons (5, 7 and 10) together with DNA from buccal swabs of RhD negative mothers. 40 samples of maternal blood (range 7-32 wks) were also tested for fetal gender since 2012. Fetal DNA was isolated from 1 ml of maternal plasma by QIAamp Circulating Nucleic Acid Kit (Qiagen, Germany) and fetal status was determined by RT-PCR method. Results: In the first phase (exon 10 only), 175 RhD+ and 97 RhD-results were detected, 9 plasma samples (3,3%) were non-informative. 144 samples were postnatally verified (52,9%) and 5 (3,47%) false RhD negative (FN) and 4 (2,77%) false RhD positive (FP) cases were then registered. In the second period (2012-2014) 73 samples were tested for three RHD exons (5, 7 and 10) together with DNA from buccal swabs of RhD negative mothers. 44 samples were RhD+, 28 RhD-and 1 sample (1,37%) non-informative. No FN and FP results were recorded postanatally. 21 cases of 40 gender determination were medically indicated due to gonosomal recessive diseases risk -mostly Hemophilia A (8x) and Duchenne muscular dystrophy (5x). Male gender was determined in 21 tested fetuses. All cases were verified postnatally, no FP neither FN results were found. Six cases of gender determination before 10wks of pregnancy (2x7,4x9) were proven correct (4x male), but the small number does not allow to draw any conclusions of testing accuracy. Conclusions: Non-invasive RhD determination with three exons (5, 7, 10) together with DNA from buccal swabs of RhD negative mothers and fetal gender determination from 10th week of pregnancy provides diagnostic accuracy.