Effect of exogenous insulin treatment on fetal growth and maternal alpha-fetoprotein levels in pregnant mice.

The effect of exogenous insulin on the maternal serum level of alpha-fetoprotein and fetal weight was studied. Insulin was given either as one subcutaneous injection on the 13th day of pregnancy (pulse treatment) or as subcutaneous injections each day throughout pregnancy (long-term treatment). Neither of the treatment procedures resulted in a significant alteration in the average fetal weight. However, pulse treatment on the 13th day of pregnancy resulted in elevated maternal serum levels of alpha-fetoprotein and in a greater number of fetuses and larger fetal mass per animal as examined on the 18th day of pregnancy. By contrast, long-term treatment with insulin from the first day of pregnancy resulted in a lower level of maternal serum alpha-fetoprotein and in significantly lower fetal mass per animal. It is concluded that insulin treatment as such, and especially the mode of treatment, plays a crucial role for fetal growth and synthesis of alpha-fetoprotein.