Intrapartum Sildenafil to Improve Perinatal Outcomes: A Randomized Clinical Trial

Importance: Sildenafil citrate may increase uteroplacental blood flow. Its ability to reduce perinatal complications related to fetal hypoxia during labor is uncertain. Objective: To compare the effectiveness of intrapartum maternal oral sildenafil citrate vs placebo in improving perinatal outcomes potentially related to intrapartum hypoxia in term pregnancies. Design, Setting, and Participants: This pragmatic, multicenter, investigator-initiated, placebo-controlled randomized clinical trial including 3257 women was conducted in 13 Australian hospitals from September 6, 2021, to June 28, 2024. The last date of follow-up (28-day neonatal mortality) was July 26, 2024. Women aged 18 years or older with singleton or dichorionic twin pregnancies, planning vaginal birth at term by either spontaneous labor or induction of labor, were recruited. Interventions: Women were assigned to 50 mg oral sildenafil citrate every 8 hours up to 150 mg or equivalent placebo. Main Outcome and Measures: The primary composite outcome was intrapartum stillbirth, neonatal death, Apgar score less than 4 at 5 minutes (a score of <4 at 5 minutes is indicative of severe neonatal depression at birth, with scores ranging from 0 to 10), acidosis at birth (umbilical cord artery pH <7.0), hypoxic ischemic encephalopathy, neonatal seizures, neonatal respiratory support for greater than 4 hours, neonatal unit admission for greater than 48 hours, persistent pulmonary hypertension of the newborn, or meconium aspiration syndrome. Secondary outcomes were the individual components of the primary composite and emergency cesarean delivery or instrumental birth for intrapartum fetal distress. Results: A total of 3257 women were randomized to sildenafil citrate (n = 1626 women and 1634 infants) or placebo (n = 1631 women and 1641 infants). Mean (SD) maternal age and gestation at randomization were similar in both groups (31.7 [5.1] vs 31.5 [5.0] years and 39.5 [1.2] vs 39.5 [1.1] weeks, respectively). A total of 868 participants (53.4%) vs 874 participants (53.6%) were of Australia/New Zealand ethnicity and 315 participants (19.4%) vs 311 participants (19.1%) were of European ethnicity. Most participants were nulliparous (944 of 1624 [58.1%; 2 missing values] vs 966 of 1630 [59.3%; 1 missing value]). Induction of labor occurred in 1353 of 1621 women (83.5%) in the sildenafil citrate group and 1348 of 1627 women (82.9%) in the placebo group. The primary outcome occurred in 83 of 1625 women (5.1%) in the sildenafil citrate group and 84 of 1625 (5.2%) in the placebo group (relative risk, 1.02; 95% CI, 0.75-1.37). Sildenafil citrate had no significant effect on emergency cesarean delivery or instrumental vaginal birth for fetal distress (relative risk, 1.12; 95% CI, 0.98-1.29) or on any of the individual components of the primary outcome. Subgroup analyses showed no evidence of heterogeneity of treatment effect. Conclusions and Relevance: Sildenafil citrate did not result in a lower incidence of adverse perinatal outcomes potentially related to intrapartum hypoxia.