Fetal weight and intrauterine position in rats

Abstract

Abstract Fetal weight data from 28 litters of Wistar rats were analyzed for the effect of position in the uterine horn on fetal weight. The deviation of each fetus from the mean weight of all fetuses in a uterine horn was divided by the standard deviation of the mean. The standard scores thus obtained were studied for position effect. A pattern of fetal weights was found in which the heaviest fetus occupied the middle position with a progressive decrease in weights toward the ovarian and cervical ends of the horn. The lightest fetus in each horn was most likely to be found occupying either one of these extreme positions. These results are discussed with respect to a hemodynamic theory of fetal growth control that has been postulated for the guinea pig and mouse, and it is concluded that this theory is not applicable to the normal rat pregnancy.