The turnover of body protein is higher after approximately 13 weeks of pregnancy, and the mother adjusts by losing less nitrogen as urea even during the first trimester. A woman who gains 12.5 kg of body weight has deposited 925 g of protein, the fetus gains 440 g, the uterus 166 g, expanded maternal blood volume contains 81 g, the placenta 100 g, and the increment in extracellular fluid 135 g. The mother probably stores some additional protein in her body, presumably in muscle. The EAR for all age groups is 0.88 g/kg/day protein or 21 g of additional protein/day. The RDA is 1.1 g protein/kg/day or 25 g/day.
One-third of the 925 g total protein deposition during the 40 weeks of pregnancy occurs in the second trimester and two-thirds in the third trimester. By the end of the third trimester, the US-Canada recommendations assume that an additional consumption of 17g protein/day is required to meet the needs for protein deposition, and since about half of this occurs during the second trimester this amounts to 8 g/day. It is also assumed that no additional protein is needed in trimester 1, but for the last two trimesters consumption of an additional 21 g/day (a total of 1.1 g/kg/day) is recommended. Recommended protein intakes for UK women are that an additional 6 g should be consumed during all three trimesters.
No UL has been set for protein, including for pregnancy, in the US-Canada recommendations due to lack of data on harmful effects. However, some earlier studies noted adverse pregnancy outcomes when high-protein supplements were given to relatively well-nourished pregnant women, so caution in this regard is certainly warranted.
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