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. The prediction of intrapartum fetal compromise is particularly important in patients undergoing induction of labor because of different indications for delivery, as this can be a useful in optimizing the method and timing of induction of labor. Objective: This study aimed to examine whether the risk of preeclampsia assessed using the Fetal Medicine Foundation algorithm (derived from a combination of maternal risk factors, mean arterial pressure, uterine arteries pulsatility index, placental growth factor, and soluble fms–like tyrosine kinase-1) is associated with the risk of intrapartum fetal compromise requiring cesarean delivery in a population of patients with singleton pregnancies undergoing induction of labor for various indications. Study Design: This was a retrospective analysis on prospectively collected data from women with singleton pregnancies who underwent routine assessments at 35 0/7 to 36 6/7 weeks of gestation at King's College Hospital (London, United Kingdom). The study outcome was the rate of fetal compromise requiring cesarean delivery, examined in relation to the risk of preeclampsia assessed at 36 weeks of gestation using the Fetal Medicine Foundation risk model. Patients who underwent spontaneous labor and prelabor cesarean deliveries were excluded. In addition, 5 risk categories for preeclampsia were created on the basis of the Fetal Medicine Foundation 36-week risk model: 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 of labor, we created 5 categories: premature rupture of membranes, postterm pregnancy (˃41 weeks of gestation), preeclampsia, fetal growth restriction (estimated fetal weight of ˂5th percentile), and preeclampsia and fetal growth restriction. A multinomial logistic regression was used to assess the risk of fetal compromise across the Fetal Medicine Foundation risk categories, accounting for all delivery outcomes (spontaneous or operative vaginal delivery and urgent cesarean delivery for fetal compromise, failure to progress, or other reasons) and allowing accurate and generalizable risk assessment of fetal compromise. Results: Of 45,375 pregnant women, 26,597 (58.6%) had spontaneous onset of labor, 6529 (14.0%) underwent elective prelabor cesarean delivery, which were excluded from the analysis. A total of 12,249 pregnant women were included, of which 182 had birth at ≤37 weeks of gestation and 1444 had fetal compromise (crude risk of 11.8%). The rate of vaginal delivery in the study population was 69.4%. The rates of fetal compromise in the 5 induction categories were 9.7% for premature rupture of membranes, 13.5% for postterm pregnancy, 14.8% for preeclampsia, 17.2% for fetal growth restriction, and 23.4% for preeclampsia and fetal growth restriction. Cases with intrapartum fetal compromise had a higher mean preeclampsia risk than cases without intrapartum fetal compromise (1/45 vs 1/81, respectively; P<.001). The risk of cesarean delivery for fetal compromise increased with (1) advancing gestational age (each week increase at 35–40 weeks: +1%; at 41–42 weeks: +5%), (2) nulliparity (+7%–10%) vs multiparity, (3) higher Fetal Medicine Foundation risk of preeclampsia (from the low-risk category of <1/50 to the high-risk category of ≥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 postterm pregnancy. Conclusion: Our study highlights the clinical use of the Fetal Medicine Foundation 36-week PE risk model in determining the risk of fetal compromise requiring cesarean delivery after induction of labor. The same model can be combined with standard obstetric indications to induction of labour to establish the risk of fetal compromise requiring cesarean delivery. Therefore, the Fetal Medicine Foundation 36-week PE risk model can be used to optimize induction of labor.