Reducing the risk of fetal distress with sildenafil study (RIDSTRESS): a double-blind randomised control trial

Liam Dunn, Vicki Flenady, Sailesh Kumar

Labour is perhaps the most hazardous time in pregnancy. As many as 20 % of cerebral palsy cases in term infants result from intrapartum events and up to 63 % of babies who develop intrapartum compromise have no prior risk factors. Sildenafil citrate (SC), a phosphodiesterase 5 inhibitor, improves uterine blood supply through vasodilatation and potentially could improve placental perfusion and hence reduce the risk of intrapartum fetal hypoxia. The aim of this study is to evaluate the efficacy of SC to reduce the risk of intrapartum fetal compromise and the need for emergency operative delivery. This is a single centre, double-blind, randomised, phase II clinical trial of SC or placebo given during labour to women (18-50 years of age) with a single, appropriately grown, non-anomalous baby at term (37-42 weeks gestation). Those with cardiovascular, renal, hepatic, ocular or hypertensive disease or contraindication to SC will be excluded. Participants will be randomised to either SC 50 mg or placebo capsules eight hourly (SC maximum 150 mg) to commence when admitted to birth suite for management of labour. Within 3 h of the first dose, a repeat ultrasound scan will be performed to measure any changes in uteroplacental and fetal Doppler indices. Labour will continue otherwise in accordance with hospital clinical guidelines. The primary outcome is emergency caesarean section for intrapartum fetal compromise. Secondary outcomes include the effect of SC on fetal and uteroplacental blood flow, meconium liquor, fetal heart rate abnormalities and neonatal outcomes (admission to neonatal intensive care, Apgar <7 at 5 min, cord pH <7.1 or lactate >4.0 mmol/L, neonatal encephalopathy, death). This is the first reported study evaluating the efficacy of SC on reducing the risk intrapartum fetal compromise. Australian New Zealand Clinical Trial Registry ACTRN12615000319572.