Fetal weight and intrauterine position in rats

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.

Fetal male masculinization in control and prenatally stressed rats

“…At Day 18, when AGD was expressed as a ratio to body weight or when body weight was examined alone relative to intrauterine position, fetuses at the mid-horn positions had heavier somatic weights than fetuses at the cervical location. These data verify earlier reports that examined the relationship between absolute intrauterine position and fetal body weight (Barr et al, 1969;Bruce & Norman, 1975;Cornwall, Carter, & Bradshaw, 1984). Futhermore, a significant difference in AGD was obtained with the MANOVA between fetuses located in the right and the left uterine horns.…”

“…For example, one important intervening variable is the intrauterine location of the fetus. Several investigators have demonstrated that rat fetuses, regardless of sex, weigh significantly more at the mid-horn positions than do fetuses located at the cervical and ovarian locations (Ban-, Jensh, & Brent, 1969;Norman & Bruce, 1979). For the MANOVA, a general linear model contained the following fetal data obtained for Scott & Carter, 1980).…”

Developmental effects of the uterine environment: dependence on fetal sex in rats

“…In polytocous species with bicornuate uteri, fetal body weight is inversely proportional to the number of fetuses present in both the ipsilateral and the contralateral uterine horns (Ibsen, 1928 ; Hammond, 1935;Barcroft, 1944; Hashima, 1956;McLaren & Michie, 1959Healy, McLaren & Michie, 1960;McCarthy, 1965;McLaren, 1965;Barr, Jensh & Brent, 1969. This influence of the uterine environment has been explained on the basis of competition among fetuses for a relatively limited supply of nutrients (Ibsen, 1928;Hammond & Marshall, 1952;McCance, 1962), space (Ibsen, 1928;Barcroft, 1944;McLaren, 1965), and/or uterine vasculature (Eckstein, McKeown & Record, 1955;McCance, 1962;McLaren, 1965).…”

“…Fetal growth is also affected by intrauterine position, although species differ in the location of the most and least favourable developmental sites (Ibsen, 1928;Rosahn & Greene, 1936;Mossman, 1937;Hashima, 1956;Waldorf, Foote, Self, Chapman & Casida, 1957;McLaren & Michie, 1959Healy et al, 1960;McLaren, 1965;Barr et al, 1969. Intrauterine position effects have been attributed to differential implantation time (Mossman, 1937), uteroplacental haemodynamics (McLaren & Michie, 1959Healy et al, 1960;McLaren, 1965), mechanical constraints imposed by the uterus (Ibsen, 1928;McLaren, 1965), and other unknown factors .…”

Polytocus focus: Uterine position effect is dependent upon horn size

“…The uterine position effect for fetal body weight in the rat, contrary to the data for mice, rabbits and lightweight pigs, initially described the heaviest fetuses being found at the mid-horn position whereas the lightest fetuses were located at the extreme cervical and ovarian ends (Barr et al, 1969). This inverted U-shaped curve of fetal body weight as a function of intrauterine position has since been replicated in numerous studies Jensh et al, 1970;Padmanabhan and Singh, 1981).…”