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Title: Unlike pregnant adult women, pregnant adolescent girls cannot maintain glycine flux during late pregnancy because of decreased synthesis from serine

Author
item HSU, JEAN - Children'S Nutrition Research Center (CNRC)
item THAME, MINERVA - University Of The West Indies
item GIBSON, RACHEL - University Of The West Indies
item BAKER, TAMEKA - University Of The West Indies
item TANG, GRACE - Children'S Nutrition Research Center (CNRC)
item CHACKO, SHAJI - Children'S Nutrition Research Center (CNRC)
item JACKSON, ALAN - Southampton General Hospital
item JAHOOR, FAROOK - Children'S Nutrition Research Center (CNRC)

Submitted to: British Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2015
Publication Date: 3/1/2016
Citation: Hsu, J.W., Thame, M.M., Gibson, R., Baker, T.M., Tang, G.J., Chacko, S.K., Jackson, A.A., Jahoor, F. 2016. Unlike pregnant adult women, pregnant adolescent girls cannot maintain glycine flux during late pregnancy because of decreased synthesis from serine. British Journal of Nutrition. 115(5):759-763.

Interpretive Summary: During pregnancy, two compounds called glycine and serine become more important because they supply another compound called methyl, which the fetus uses to make its DNA. Also, as the fetus grows large amounts of glycine are needed to make a protein called collagen, which is used as the framework for skin, bones, blood vessels, and other body tissues. A woman gets glycine and serine from two sources, the amount she makes in her body plus the amount she gets from the protein in her meals. In an earlier study, we found that pregnant teenagers made less glycine in late pregnancy compared to adult women. As serine is used to make most glycine in the body, in this study we wanted to compare how much serine and glycine the pregnant girls were making compared to adult women in early and late pregnancy and how much of glycine was being made from serine. We found that pregnant teenagers made less glycine in late pregnancy when they should be making more, because they were converting less serine to glycine. The teenagers who made less glycine had shorter babies at birth. It is therefore possible that the pregnant teenager cannot make enough collagen for her baby to grow normally because she is not making enough glycine in late pregnancy. Eating more protein in her meals late pregnancy will provide her with more glycine and serine, which may solve this problem.

Technical Abstract: During pregnancy, glycine and serine become more important because they are the primary suppliers of methyl groups for the synthesis of fetal DNA, and more glycine is required for fetal collagen synthesis as pregnancy progresses. In an earlier study, we reported that glycine flux decreased by 39% from the first to the third trimester in pregnant adolescent girls. As serine is a primary precursor for glycine synthesis, the objective of this study was to measure and compare glycine and serine fluxes and inter-conversions in pregnant adolescent girls and adult women in the first and third trimesters. Measurements were made after an overnight fast by continuous intravenous infusions of 2H2-glycine and 15N-serine in eleven adolescent girls (17.4 (se 0.1) years of age) and in ten adult women (25.8 (se 0.5) years of age) for 4 h. Adolescent girls had significantly slower glycine flux and they made less glycine from serine in the third (P<0.05) than in the first trimester. Baby birth length was significantly shorter of adolescent girls (P=0.04) and was significantly associated with third trimester glycine flux. These findings suggest that the pregnant adolescent cannot maintain glycine flux in late pregnancy compared with early pregnancy because of decreased synthesis from serine. It is possible that the inability to maintain glycine synthesis makes her fetus vulnerable to impaired cartilage synthesis, and thus linear growth.