Amniotic fluid hIGFBP-1 levels across gestation. Total hIGFBP-1 levels in amniotic fluid were measured by a species-specific immunoradiometric assay. The data compare hIGFBP-1 levels between (a) wild-type and transgenic females and (b) wild-type and transgenic fetuses from F+/M– matings. Data represent mean hIGFBP-1 levels in amniotic fluid from 15–25 fetuses. Black bars, transgenic; white bars, wild-type. *P <0.01 for e17.5 transgenic versus wild-type.