Maternal Administration of Sildenafil Citrate Alters Fetal and Placental Growth and Fetal-Placental Vascular Resistance in the Growth-Restricted Ovine Fetus

Intrauterine growth restriction (IUGR) causes short- and long-term morbidity. Reduced placental perfusion is an important pathogenic component of IUGR; substances that enhance vasodilation in the uterine circulation, such as sildenafil citrate (sildenafil), may improve placental blood flow and fetal growth. This study aimed to examine the effects of sildenafil in the growth-restricted ovine fetus. Ewes carrying singleton pregnancies underwent insertion of vascular catheters, and then, they were randomized to receive uterine artery embolization (IUGR) or to a control group. Ewes in the IUGR group received a daily infusion of sildenafil (IUGR+SC; n=10) or vehicle (IUGR+V; n=8) for 21 days. The control group received no treatment (n=9). Umbilical artery blood flow was measured using Doppler ultrasound and the resistive index (RI) calculated. Fetal weight, biometry, and placental weight were obtained at postmortem after treatment completion. Umbilical artery RI in IUGR+V fell less than in controls; the RI of IUGR+SC was intermediate to that of the other 2 groups (mean±SEM for control versus IUGR+V versus IUGR+SC: ∆RI, 0.09±0.03 versus -0.01±0.02 versus 0.03±0.02; F(2, 22)=4.21; P=0.03). Compared with controls, lamb and placental weights were reduced in IUGR+V but not in IUGR+SC (control versus IUGR+V versus IUGR+SC: fetal weight, 4381±247 versus 3447±235 versus 3687±129 g; F(2, 24)=5.49; P=0.01 and placental weight: 559.7±35.0 versus 376.2±32.5 versus 475.2±42.5 g; F(2, 24)=4.64; P=0.01). Sildenafil may be a useful adjunct in the management of IUGR. An increase in placental weight and fall in fetal-placental resistance suggests that changes to growth are at least partly mediated by changes to placental growth rather than alterations in placental efficiency.