The PRISM pilot feasibility study consists of two phases to determine: 1) to delivery practices, rates of primary and secondary outcomes, and feasibility of enrollment rates, and 2) to assess the feasibility and acceptability of the intervention and expected enrollment rates, and estimate the effect size of sildenafil citrate on maternal and neonatal outcomes in a low resource settings in preparation for the main RCT.

The primary objectives of the PRISM pilot study relate to feasibility of a large randomized controlled trial of intrapartum sildenafil citrate and will aid in design of a definitive trial among pregnant women to day 42 postpartum (pp) and their newborns to day 28 pp. The pilot will help prepare for the main trial by allowing the investigators to:

• Determine the rate and indication for fetal heart rate monitoring practices;
• Determine the rate and indications for operative delivery;
• Inform the rates of relevant primary and secondary outcomes to possibly target in a large randomized controlled trial of intrapartum sildenafil citrate;
• Assess the feasibility and acceptability of the intervention and expected enrollment rates;
• Estimate the effect size of sildenafil citrate on maternal and neonatal outcomes in a low resource setting.

Inclusion Criteria:

• Admission to facility with plan for spontaneous or induced vaginal delivery
• Early stage of labor (≤ 6 cm cervical dilation per local standard) at ≥ 37 weeks gestation
• Age ≥ 18 years of age
• Presence of single live fetus confirmed via a fetal heart rate by Doptone in cephalic position
• Provision of written informed consent [Note: if written consent is obtained at an early time, verbal re-confirmation is required at time of enrollment]

Exclusion Criteria:

• Non-emancipated minors (as per local regulations)
• Plan for Cesarean delivery or history of cesarean section prior to enrollment*
• Unknown gestational age
• Advanced stage of labor (>6 cm or 10 cm cervical dilation per local standards) and pushing or too distressed to understand, confirm, or give informed consent regardless of cervical dilation
• Not capable of giving consent due to other health problems such as obstetric emergencies (for example, antepartum hemorrhage) or mental disorder;
• Any medical condition considered a contraindication, including contraindication to sildenafil therapy, per the judgement of site investigators
• Any maternal medical condition or status that precludes informed consent
• Recognized fetal anomaly

Pregnant women who are delivering in a participating health facility will be screened for eligibility

The pilot observational study will be undertaken in two sites in Zambia; one in a Level 3 delivery facility and a Level 2 delivery facility in Lusaka. A maximum of 1000 women per site will be enrolled in the pilot study. Each site will prospectively collect up to six months of data, three months of piloting forms and non-drug interventions. A subsequent small RCT with study medication will enroll 500 participants over a period of up to three months per site. Enrollment will take place in pre-identified health facilities where women present for labor and delivery.