Does sildenafil reduce the risk of fetal distress in labour?

Labour is perhaps the most hazardous time in pregnancy for the fetus. Uterine contractions can contribute to more than a halving of blood flow to the uterus and placenta and this in turn may lead to fetal distress. In most pregnancies, the placental blood supply and function is adequate but it may not be sufficient to tolerate the extra demands of labour. Up to 63% of babies who become distressed and suffer oxygen deprivation in labour have no prior risk factors. Furthermore, events in labour account for as many as 20% of cases of cerebral palsy in term infants. Recent research demonstrates that the changes in blood flow to the fetus can be detected by ultrasound and that these changes are highly predictive of identifying fetuses at risk of becoming distressed in labour, as well as reliably excluding those that were not at risk. With this in mind, investigating ways to preserve and promote the blood supply and in turn, the oxygenation to the fetus has the potential to significantly change intrapartum care. Sildenafil is a vasodilator (opens blood vessels) and based on previous research may play a role in enhancing blood flow to the fetus. This clinical trial will investigate if having sildenafil in labour improves the blood flow to the fetus and reduces the need for emergency operative delivery (either caesarean section or operative vaginal birth) for fetal distress.