Postnatal development of rats born preterm and postterm. I. Body weight.

Abstract

Litters with 3 preterm, 3 term and 3 postterm littermates have been fed by one mother each. Fetal body weight continues to increase in utero if the normal gestational period is extended by 1 day. But this intrauterine weight gain is smaller than the postnatal weight gains of term rats of the same conceptional ages. While the body weights of term and postterm rats increase rapidly immediately after birth, there is a lag phase of 3 days in preterm animals. This delay in weight gain is not caught up during a period of 30 postnatal days. This appears to be due to malnutrition in the early postnatal period. After the 20th day of life, the weight gain markedly increases in all groups, indicating the effect of supplemental feeding in the weaning period.