TIMING OF GESTATION IN RATS BY FETAL AND MATERNAL WEIGHTS

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  • 1 January 1978
    • journal article
    • research article
    • Vol. 42  (1) , 43-53
Abstract
Weights of embryonic and fetal rats increase with gestational age from days 13-20 in a strictly logarithmic manner and then slow. Data for other rat strains show substantially the same growth curves and same weights as the inbred Kx strain studied. During this late gestational period fetal weights doubled every 1.22 days. An earlier period of somewhat faster growth can be inferred. These growth rates are virtually the same as maximum rates at which rat neoplasms can grow. A regression equation was constructed from which ages of rat embryos can be predicted from their weights within confidence limits of .+-. 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 2 procedures facilitate routine production of embryos of known age for experimental purposes.

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