First trimester combined screening for preeclampsia in twin pregnancies - results of the first 100 twin pregnancies included in the IPSISS (Implementing Preeclampsia Screening in Switzerland) cohort.

Background
Preeclampsia (PE) is more common in twin than in singleton pregnancies. First trimester combined screening including maternal risk factors, uterine artery pulsatility index (UtA-PI), mean arterial pressure (MAP) and placental growth factor (PlGF) is possible in twin pregnancies. However, the performance is reported to be inferior compared to singletons.Objective
The objective of this trial was to assess the performance of PE-screening in the first 100 twin pregnancies included in the IPSISS cohort in Switzerland.Study Design
This is a prospective multi-center registry study performed in Switzerland, including all twin and singleton pregnancies included in the registry with complete screening parameters and outcome data, between June 2020 and June 2024. 3263 singleton and 104 twin pregnancies were included in this analysis. Pregnancies considered at risk for preterm PE were prescribed low dose aspirin (LDA) according to local guidelines. All parameters were converted to multiple of medians (MoM) by the online calculator on the FMF website (The Fetal Medicine Foundation. Calculators. Research Tools. https://fetalmedicine.org/research/peRisk). Parameters were compared between singleton, monochorionic (MC) and dichorionic (DC) twins. Statistical analysis was performed with GraphPad Prism 10.0 for Windows.. Continuous variables were analysed using the Student t-test or Mann-Whitney U-test while proportions were evaluated utilizing the Fisher's exact test or Chi2 test and Kruskal Wallis test.Results
The incidence of preterm preeclampsia (pPE) in singleton pregnancies with live birth was 29/3'221 (0.9%) compared to 5/101 (5.0%) in twins. In uneventful pregnancies, median MAP [IQR] was significantly higher in MC twins compared to singletons, but not in DC twins (88.5mmHg [85.4-98.0] versus 86.3mmHg [81.0-91.5], (p=0.005)). Median UtA-PI [IQR] was significantly lower in DC twins compared to singletons and MC twins (1.40 [1.05-1.65] vs 1.50 [1.20-1.9] (p=0.0006) and 1.60 [1.35-1.80] (p=0.022) respectively). Median PlGF [IQR] was significantly higher in DC twins than in singletons, but not in MC twins (55.0pg/ml [43.5-79.1] versus 41.0pg/ml [31.0-53.8], (p<0.0001)) and median PAPP-A [IQR] was significantly higher in both DC and MC twins compared to singletons (9.72IU/l [5.12-14.06] and 6.89IU/l [4.13-11.59] vs 3.25IU/l [1.81-5.15] (p<0.0001) respectively). In twin pregnancies that later developed pPE, PlGF-MoM [IQR] was significantly lower than in uneventful twin pregnancies (0.52 MoM [0.44-0.81] vs 0.99 MoM [0.67-1.41], (p=0.012)), while all other markers showed no significant difference. At a fixed screen positive rate (SPR), significantly more twin pregnancies with pPE were screen negative than singleton pregnancies with pPE.Conclusion
This study demonstrated that in our cohort the markers perform as expected in twin compared to singleton pregnancies, and that at fixed SPR, fewer twin pregnancies with later PE were detected compared to singletons. Our preliminary results showed that a higher cut-off than 1:100, with a corresponding higher SPR, must be chosen when screening for pPE in twin pregnancies, in order to achieve an acceptable detection rate.Tweetable Abstract
Analysis of preeclampsia screening in the first 100 twin pregnancies included in the IPSISS cohort showed that a higher cut-off than 1:100 must be used to screen for preterm preeclampsia in twins.