Background: Serum PAPP-A is part of first trimester Down syndrome screening. Low levels have been associated with adverse outcome and chromosomal abnormality.
Aims: To assess the incidence of adverse outcome when PAPP-A levels are at or below 0.2 multiples of the median (MoM).
Methods: Consecutive patients attending a first trimester screening program were collected. Those with low PAPP-A levels were divided into 3 groups: < 0.1MoM; 0.11 - 0.15MoM; and 0.16 – 0.2MoM.
Results: Screening 44535 patients resulted in 197 with PAPP-A levels < 0.2 MoM (31, 54 and 112 cases for the 3 groups respectively). The incidence of karyotypic abnormality increased with decreasing PAPP-A levels. In the absence of chromosome abnormality, pregnancy outcomes were defined as "normal " in at least 30% and "good" in at least 60%, with both percentages increasing as the PAPP-A level rose. The incidence of prematurity was similar in the 3 groups, but higher than the statewide average, while the incidence of extreme prematurity appeared to be related to reducing PAPP-A levels. The incidence of growth restriction in the 3 groups was similar, but was still double the incidence in the normal population.
Conclusion: If the PAPP-A level is < 0.2 MoM and the karyotype is normal, there is an increased risk of adverse outcome, becoming more likely with further reduction in PAPP-A levels. Even with PAPP-A below 0.1 MoM, a good outcome can be expected in 60% of cases. Careful morphological assessment is suggested and later monitoring of fetal growth and well being.