Primary composite outcome
| Components of composite primary end point | Rate (%) | Association with long-term adverse outcome |
| Intrapartum stillbirth70 | 0.1* | – |
| 28-day neonatal mortality | 0.24 | – |
| Apgar score <4 at 5 min | 0.5 | ↑ Risk of cerebral palsy71 |
| Umbilical cord artery pH <7.0 | 2.2† | ↑ Risk of Hypoxic Ischaemic Encephalopathy (HIE)72 |
| Neonatal encephalopathy Sarnat grade 2 or 373 | 0.5 | ↑ Risk of death or disability74 |
| Neonatal seizures‡73 | 0.25 | ↑ Risk of death or disability74 |
| Neonatal respiratory support for >4 hours | 3.6 | ↑ Risk of cerebral palsy75 |
| Neonatal unit admission for >48 hours | 4.3 | ↑ Asthma after term respiratory morbidity76 |
| Persistent pulmonary hypertension73 | 0.04 | ↑ Risk of death or disability77 |
| Meconium aspiration73 | 0.75 | ↑ Risk of death or disability78 |
| Total (corrected for overlap) | 7.0 |
*Based on data from Grobman et al.20
†Based on data from Yeh et al.72
‡Although seizures include non-encephalopathic causes like stroke or metabolic disorders, in a randomised trial, those causes not influenced by sildenafil will tend to be evenly balanced between study arms and therefore tend not to bias the comparison. In this pragmatic trial, seizures, persistent pulmonary hypertension and meconium aspiration are all defined using local protocols.