First trimester risk of preeclampsia and rate of spontaneous birth in patients without preeclampsia

Background First-trimester screening for preeclampsia (PE), by a combination of maternal risk factors and mean arterial pressure (MAP), uterine artery pulsatility index (UtA-PI) and placental growth factor (PlGF), as proposed by the Fetal Medicine Foundation (FMF) provides effective prediction of preterm PE. Placental dysfunction is a potential precursor of spontaneous birth. Objective The objective of this study is to examine whether the estimated risk of PE is associated with the gestational age at onset of spontaneous delivery in the absence of PE. Study Design This was a secondary analysis of the data from the SPREE trial, in which there was comparison in the performance of first-trimester screening for preterm PE by the FMF model vs. a traditional history-based risk scoring system. The population for the present study included only the subgroup of women with spontaneous onset of delivery (labor with intact membranes or preterm prelabor rupture of membranes) and was arbitrarily divided into three groups according to the risk for preterm PE assessed by the FMF model at 11-13 weeks’ gestation: group 1 (low risk, ˂1/100), group 2 (intermediate-risk, 1/50 to 1/100) and group 3 (high-risk, ˃1/50). A survival analysis was carried out with Kaplan-Meier estimator and a Cox regression analysis stratified according to three PE risk groups. Gestational age at spontaneous birth in the study groups was compared by means of Log-rank test and Hazard Ratio (HR). Results The study population comprised of 10,820 cases with delivery after spontaneous onset of labor, among the total of 16,451 cases participating in SPREE. There were 9795 cases in group 1,583 in group 2, and 442 in group 3. The gestational age at delivery was <28, <32, <35, <37 and <40 weeks in 0.29%, 0.64%, 1.68%, 4.52% and 44.97%, respectively, in group 1, 0.69%, 1.71%, 3.26%, 7.72% and 55.23% in group 2 and 0.45%, 1.81%, 5.66%, 13.80% and 63.12% in group 3. The curve profile of gestational age at spontaneous birth in the three study groups was significantly different overall and in pairwise comparisons (p-values <0.001). Cox regression analysis showed risks increase for spontaneous birth of 18% when comparing intermediate-risk vs. low-risk (p˂0.001) and 41% when comparing high-risk vs. low-risk categories (p˂0.001). Conclusions In this study investigating birth after spontaneous onset of labor in women without PE, there are two major findings. First, the duration of pregnancy decreases with increasing first-trimester risk for PE. Second, in a high-risk group, compared to a low-risk group, the risk of spontaneous birth is 4-times higher at 24-26 weeks, 3-times higher at 28-32 weeks, and 2-times higher at 34-39 weeks. These differences present major clinical implications for antepartum counselling, monitoring and interventions in these pregnancies.