The relation of the uterine vasculature to fetal growth and the intrauterine position effect in rats

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Abstract
Ligation of the uterine vasculature was performed on the 10th or 18th day of gestation in 114 Wistar rats. In each rat the blood vessels of one uterine horn were ligated at the level of the oviduct, midhorn, or the cervix; the opposite horn served as a control. Fetal weight and mortality data were analysed for the effect of the vascular interruption and the effect of intrauterine position. It was found that patency of the ovarian artery was not essential for normal fetal growth and that the loop‐artery configuration of the vessels to the uterine horn was not a determinant of the position effect. The time in gestation at which the ligation was performed had a decided effect on ultimate fetal weight: the later in gestation, the greater the fetal growth retardation. Various factors that could be responsible for the position effect are discussed. It is suggested that the association between fetal weight and intrauterine position is species dependent and is determined by unknown factors, not singly by hemodynamics, myometrial pressure, or time of implantation.