['This study investigated the effects of inhibition of vascular endothelial growth factor (VEGF) during the first postpartum cycle in marmosets housed with a fertile male where a 90% fertility rate is normal.', 'On resumption of mating, females were treated with either 25 mg/kg aflibercept, a potent VEGF inhibitor, or control Fc protein (n=6 per group) at the time of ovulation. Effects on timing of pregnancy were monitored by measuring plasma progesterone, chorionic gonadotropin (CG) and uterine palpation.', 'In five of six Fc-treated controls, the postpartum rise in progesterone was maintained and followed by a sustained rise in CG by Day 30 posttreatment indicating pregnancy. In all six aflibercept-treated animals, progesterone secretion was suppressed in the treatment cycle and a CG rise did not occur by Day 30. Pregnancy was delayed to the next cycle, significantly extending interbirth interval compared to controls. Posttreatment deliveries and infant development were normal.'] Does inhibition of vascular endothelial growth factor during the postovulatory period prevent pregnancy in the marmoset?