The peak velocity for fetal weight gain occurs in the last few weeks of pregnancy. As the fetus matures, it swallows and absorbs an increasing amount of amniotic fluid, which contributes to the growth of the fetus. The authors studied cases of small intestinal atresia (IA) treated over 9 years to determine whether amniotic fluid has any nutritive role in the development of human fetus, and if it does, at what stage of gestation is the contribution of amniotic fluid significant to fetal nutrition. Fifty-nine newborns had IA (24 jejunal, 35 ileal). Ten of the patients had associated anomalies (3 cystic fibrosis, 2 congenital heart disease, 1 neural tube defect, 1 microcephaly, 2 malrotation, 1 vesicoureteric reflux). Among the 24 babies with jejunal atresia, one was a twin, and birth weight was not recorded for another. These two patients were excluded from the study. Of the remaining 22 patients with jejunal atresia, 10 were born before 36 weeks' gestation; only five of 35 patients with ileal atresia were born before 36 weeks' gestation. Fourteen patients were below the 10th percentile for birth weight after correction for gestational age, one was born before 36 weeks, and 13 were born after 36 weeks. Five (41.7%) of the 12 patients with jejunal atresia who were born after 36 weeks' gestation were underweight, as were eight (26.7%) of the 30 patients with ileal atresia. Thus, it appears that amniotic fluid contributes to the fetal growth in the last few weeks of gestation, and the higher the obstruction in the small intestine, the more pronounced the effect on the nutrition of the fetus.