Induced preterm birth in sheep: a suitable model for studying the developmental effects of moderately preterm birth.

Our aim was to characterize an ovine model of preterm birth that allows analysis of the developmental effects of preterm birth in the absence of postnatal confounding factors. Preterm birth was induced at 131 days of gestation in 82 lambs; controls (n = 31) were born at term (145 days). Overall survival of preterm lambs was 60%; males had significantly lower survival than females (44% vs 76%); 94% of term lambs survived. Although the birth weight of preterm lambs was approximately 0.9 kg lower than in term lambs, the crown-to-rump and forelimb lengths were similar. At 9 weeks after term-equivalent age, there were no differences in body weight or dimensions between preterm and term lambs; when adjusted for body weight, the heart was 21% heavier in preterm than term lambs. We conclude that moderately preterm birth in sheep is characterized by a greater survival of female lambs than males and has significant effects on organ development.