OC17.08: Levels of cell free fetal DNA can be used to differentiate between mild and severe pre‐eclampsia, but is not predictive of SGA

To investigate whether levels of cell free fetal DNA (cffDNA) assessed at 25 weeks gestation when determining fetal RHD status and PAPP-A from the combined first trimester risk assessment for trisomy 21 can identify women at risk of developing pre-eclampsia and SGA neonates. A population of 964 singleton pregnant RhD negative women with an RHD positive fetus who participated in the antenatal RHD screening programme in the Capital Region of Denmark. All women had a first trimester nuchal translucency scan and a 20 week malformation scan. Gestational age was based on CRL measurement at first trimester screening, PAPP-A was measured at 8–14 weeks. SGA was calculated using the regression equation constructed by Marsál and co-workers. We used a standard dilution curve to calculate the amounts of cffDNA. A total of 38 women developed pre-eclampsia (3.9%), 15 cases of severe and 23 cases of mild pre-eclampsia. The number of neonates born SGA was 51 (5.3 %). The OR of developing mild pre-eclampsia given a cffDNA level below the 5th centile was 4.1 (95% CI: 1.2–13.2) and the OR of developing severe pre-eclampsia given a cffDNA level above the 90th centile was 10.2 (95% CI: 3.4–30.4). SGA was significantly associated with fetal DNA levels above the 90th centile (P = 0.009). Amongst women diagnosed with pre-eclampsia 46% in the group with cffDNA levels above the 90th centile delivered an SGA neonate compared to 7% in the group with cffDNA levels below the 90th centile. Amongst women not developing pre-eclampsia the numbers were 7.1% versus 4.5%. PAPP-A levels below the 5th centile were associated with mild pre-eclampsia, but not with SGA. Cell free fetal DNA is a marker for pre-eclampsia. High levels were associated with severe pre-eclampsia, low levels with mild pre-eclampsia, thus indicating different placental pathologic mechanisms. High levels of cffDNA is a poor marker of SGA independently of pre-eclampsia.