Summary: The head is more than 1/3 of entire length at 9 weeks of gestation, ~1/4 length at birth and ~1/8 length in the adult. Maternal environment controls fetal growth. Embryonic growth depend upon growth factors and new born mice lacking insulin-like growth factor 2 (IGF-2) are only 60% of normal birth size. Growth hormone (GH) is secreted throughout fetal life and secretion by the
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