The 36-week preeclampsia risk by the Fetal Medicine Foundation algorithm is associated with fetal compromise following induction of labor.

Background: Previous studies demonstrated that placental dysfunction leads to intrapartum fetal distress, particularly when an abnormal pattern of angiogenic markers is demonstrated at 36 weeks of gestation. Prediction of intrapartum fetal compromise is particularly important in patients undergoing induction of labor due to different indications for delivery, as this can be a useful in optimizing the method and timing of the induction.

Objective: To examine whether the risk of preeclampsia assessed by the Fetal Medicine Foundation (FMF) algorithm (derived from a combination of maternal risk factors, mean arterial pressure, placental growth factor and soluble fms-like tyrosine kinase-1), associates with the risk of intrapartum fetal compromise requiring cesarean delivery, in a population of singleton pregnancies undergoing labor induction for various indications.

Study Design: Retrospective analysis on prospectively collected data from women with singleton pregnancies undergoing routine assessments at 35 to 36 weeks of gestation at King's College Hospital (London, UK). The study outcome was the rate of fetal compromise requiring cesarean delivery, examined in relation to the risk of preeclampsia assessed at 36 weeks by the FMF algorithm. Patients undergoing spontaneous labor and prelabor cesarean deliveries were excluded. Five risk categories for preeclampsia were created based on the 36 weeks FMF algorithm: A:˃1/2; B:1/2 -1/5; C: 1/5-1/20; D:1/20-1/50 and E:˂1/50. Based on the reason for induction, we created five categories: premature rupture of membranes; post-term (˃41 weeks), preeclampsia, fetal growth restriction (estimated fetal weight ˂5th centile), preeclampsia and fetal growth restriction. A multinomial logistic regression was used to assess the risk of fetal compromise across the FMF risk categories and accounting for all delivery outcomes (spontaneous or operative vaginal delivery and urgent cesarean delivery for fetal compromise, failure to progress or other reasons), allowing accurate and generalizable risk assessment of fetal compromise.

Results: Of 45,375 screened pregnancies, 26,597 (58.6%) had spontaneous onset of labor, 6529 (14.0%) underwent elective pre-labor cesarean delivery, and these were excluded from the analysis; 12,249 were included, of which 182 had a gestational age at birth ≤37 weeks and 1,444 had fetal compromise (crude risk 11.8%). The rate of vaginal delivery in the study population was 69.4%. The rates of fetal compromise in the five induction categories were: 9.7% (premature rupture of membranes), 13.5% (post-term), 14.8% (preeclampsia), 17.2% (fetal growth restriction), and 23.4% (preeclampsia and fetal growth restriction). Cases with vs without intrapartum fetal compromise had higher mean PE risk (1/45 vs. 1/81; p-value < 0.001). The risk of cesarean delivery for fetal compromise increased with: i) advancing gestational age (each week increase at 35-40 weeks: +1%; at 41-42 weeks: +5%); ii) nulliparity +7-10% vs multiparity iii) higher FMF risk of preeclampsia (from the low-risk <1/50 to the high-risk category ≥1/2: +18%; with greater effect for higher preeclampsia risk). In this study population, the rates of fetal compromise were lower with diagnoses of preeclampsia and rupture of membranes and higher with fetal growth restriction (alone or in combination with preeclampsia) and post-term.

Conclusions: This study points out the clinically useful association of the 36 weeks FMF risk for preeclampsia with fetal compromise after labor induction. The combination of preeclampsia risk by the 36 weeks FMF method and major delivery indications significantly associates with intrapartum fetal compromise requiring cesarean delivery and may be used to optimize labor induction.