Induction of labour (IOL) is done for 20% of pregnancies for various maternal and fetal indications and nearly 20% of labour inductions end up in caesarean section. The most common causes are failed induction and intrapartum fetal distress. In spite of significant advances in methods of IOL and intrapartum fetal monitoring, no interventions are proven to reduce the development of intrapartum fetal distress

Inclusion Criteria:

1. Singleton pregnancy.
2. Pregnant ≥ 37 weeks gestation.
3. Fetus with longitudinal lie and vertex presentation.
4. Healthy fetus with EFW>2500 gm

Exclusion Criteria:

1. Patients with previous cesarean delivery or uterine surgery.
2. Antepartum hemorrhage.
3. Cephalopelvic disproportion.
4. Category II or III non-stress test.
5. Medical disease as hypertension, cardiac, renal and hepatic disorders
6. Intrauterine fetal death.
7. Fetal growth restriction.
8. Fetuses with major congenital malformations.
9. Women taking any anti-hypertensive medication, alpha-adrenergic blocking agents, calcium channel blockers (verapamil), nitrates, medications used to treat pulmonary arterial hypertension, and other phosphodiesterase type 5 inhibitors.
10. Women with a contra-indication to sildenafil treatment such as hypersensitivity to sildenafil.