Modest restriction of dietary protein during pregnancy in the rat: fetal and placental growth.

Pregnant rats were fed to appetite on diets containing 6, 9, 12 or 18% protein and the fetuses were delivered at 20 days. Compared with the 18% protein diet (7.4 MJ), there was a significant increase in food and energy intake in the rats on the 9% (8.7 MJ) and 12% (8.4 MJ) diets, but not on the 6% (7.4 MJ) diet. The efficiency with which the dietary energy was used for weight gain was reduced on the 6, 9 and 12% diets compared with the 18% diet. The trend towards a decrease in the number of viable fetuses and an increase in the number of resorptions on the 9% and 6% diets did not reach statistical significance. The placental weight was not different to the 18% group (520 mg) on the 12% diet (540 mg), but was significantly increased on the 9% diet (590 mg) and significantly decreased on the 6% diet (510 mg). Fetal weight was greatest on the 12% diet (1.81 g) and significantly decreased on the 9% diet (1.71 g). The fetal:placental ratio, around 3.3 for the 18 and 6% diets, was significantly increased on the 12% diet (3.7) and significantly decreased to 2.9 on the 9% diet. After adjusting for the effect of the fetal position in the uterine horn, the number of pups per litter and an estimate of the number of failed implantations the effect of diet on placental weight was no longer statistically significant, but the effect of dietary protein on fetal weight was more significant statistically, with little change overall on the fetal:placental ratio.(ABSTRACT TRUNCATED AT 250 WORDS)