Pregnancies conceived using assisted reproductive technologies (ART) have low levels of pregnancy-associated plasma protein-A (PAPP-A) leading to a high rate of false-positive results in first trimester screening for Down syndrome.

BACKGROUND First trimester screening (FTS) for Down syndrome combines measurement of nuchal translucency, free beta-human chorionic gonadotrophin and pregnancy-associated plasma protein-A (PAPP-A). The aim of this study was to undertake a detailed analysis of FTS results in singleton pregnancies conceived using assisted reproductive technologies (ART) and non-ART pregnancies. METHODS A record linkage study compared outcomes in 1739 ART-conceived and 50 253 naturally conceived pregnancies. RESULTS Overall, significantly lower PAPP-A levels were detected in ART pregnancies (0.83 multiples of median, MoM) than in controls (1.00 MoM) (t-test P < 0.001). This difference remained after excluding complicated pregnancies. Analysis of factors affecting PAPP-A levels suggested fresh compared with frozen embryo transfers and use of artificial cycles compared with natural cycles for frozen transfers were associated with lower values. The adjusted odds ratio (AdjOR) for receiving a false-positive result was 1.71 (95% CI 1.44-2.04; P < 0.001) for ART pregnancies compared with non-ART pregnancies, and this leads to a higher AdjOR (1.24, 95% CI 1.03-1.49; P = 0.02) for having a chorionic villous sampling (CVS) or amniocentesis. CONCLUSIONS ART pregnancies have reduced FTS PAPP-A levels leading to an increased likelihood of receiving a false-positive result and having a CVS/amniocentesis. Lower PAPP-A may reflect impairment of early implantation with some forms of ART.