EVIDENCE SUGGESTING THAT THE ODORTYPES OF PREGNANT-WOMEN ARE A COMPOUND OF MATERNAL AND FETAL ODORTYPES

Odortypes-namely, body odors that distinguish one individual from anot her on the basis of genetic polymorphism at the major histocompatibili ty complex and other loci-are a fundamental element in the social life and reproductive behavior of the mouse, including familial imprinting , mate choice, and control of early pregnancy. Odortypes are strongly represented in urine, During mouse pregnancy, an outcrossed mother's u rine acquires fetal major histocompatibility complex odortypes of pate rnal origin, an observation that we took as the focus of a search for odortypes in humans, using a fully automated computer-programmed olfac tometer in which trained rats are known to distinguish precisely the o dortypes of another species. Five women provided urine samples before and after birth, which in each case appropriately trained rats were fo und to distinguish in the olfactometer. Whether this olfactory distinc tion of mothers' urine before and after birth reflects in part the odo rtype and hence genotype of the fetus, and not just the state of pregn ancy per se, was tested in a second study in which each mother's postp artum urine was mixed either with urine from her own infant or with ur ine of a different, same-aged infant. Responses of trained rats were m ore positive with respect to the former (congruous) mixtures than to t he latter (incongruous) mixtures, implying that, as in the mouse, huma n fetal odortypes of paternal genomic origin are represented in the od ortype of the mother, doubtless by circulatory transfer of the pertine nt odorants.