Timing of gestation in rats by fetal and maternal weights
Knox, W.E.; Lister-Rosenoer, L.M.
Growth 42(1): 43-53
1978
ISSN/ISBN: 0017-4793 PMID: 566694 Document Number: 134351
Weights of embryonic and foetal rats increase with gestational age from day 13 to 20 in a strictly logarithmic manner and then slow down. Findings for other rat strains published as long ago as 1915 show substantially the same growth curves and the same weights as the inbred Kx strain studied. During this late gestational period foetal weights doubled every 1.22 days. An earlier period of faster growth can be inferred. These growth rates are about the same as the fastest rates at which rat neoplasms can grow. A regression equation was constructed from which the ages of rat embryos can be predicted from their weights within confidence limits of plus or minus 0.24 days. A similar logarithmic increase of added weight in the pregnant dam was recognized by which pregnancies could be conveniently diagnosed as early as day 7. These two procedures allow the routine production of embryos of known age for experimental purposes.