Nitric oxide plays a crucial role in several aspects of female reproductive physiology including menstruation, conception, , ovarian function, sperm motility and implantation. Increased nitric oxide production may be involved in the normal haemodynamic changes of pregnancy, in the maintenance of the uteroplacental circulation and in the control of maternal vascular tone, while a deficit in nitric oxide may contribute to the pathophysiology of intrauterine growth restriction and preeclampsia. There is considerable evidence that nitric oxide is involved in inhibition of uterine contractility during pregnancy and in the process of cervical ripening at the onset of labor.