During pregnancy, growth of the foetus depends on an adequate glycine supply because it is needed for synthesis of fetal DNA, collagen and serine. Since pregnant adolescent girls give birth to lower birth weight babies, it is possible that they do not produce sufficient glycine to meet overall demands as their adult counterparts, especially after an overnight fast. The objective of the study was to measure and compare the flux of glycine among adolescents and adult women in the first and third trimesters of pregnancy. Glycine flux was measured by continuous intravenous infusion of 2 H 2 -glycine in eight overnight fasted adolescents and in eight adult women in the first and third trimesters of pregnancy. There was a significant interaction between subject's age and time of pregnancy (P¼ 0·02), as weight-specific glycine flux decreased by 39 % from trimesters 1 to 3 in the adolescents but increased by approximately 5 % in the adults. Whole body glycine flux also decreased significantly in the adolescent group (P, 0·05) from trimesters 1 to 3, and this was associated with a significant reduction in plasma glycine concentration. In trimester 3, there was a positive correlation between glycine flux and the subject's age indicating that younger subjects had slower fluxes. These findings suggest that after a brief period of food deprivation, the pregnant adolescent cannot maintain glycine production as her adult counterpart in late pregnancy. It is possible that this inability to maintain endogenous glycine production makes her foetus more vulnerable to impaired growth if food deprivation becomes more frequent or is prolonged.Adolescent pregnancy: Glycine flux: Low birth weight: First trimester: Third trimester

These findings suggest that, in the fasted state in late pregnancy, pregnant adolescents cannot increase weight-specific glucose production by the same magnitude as their adult counterparts. Furthermore, whereas adult women increase glucose production primarily through gluconeogenesis, adolescents do so through glycogenolysis.

NO has been proposed as a mediator of vascular expansion during pregnancy. Inability to increase NO synthesis and/or production of its precursor, arginine, may contribute to pregnancy-induced hypertension. Adolescents have a higher incidence of gestational hypertension. It is not known whether pregnant adolescents can produce sufficient arginine to meet overall demands. Our objective was to measure and compare the arginine flux and NO synthesis rates of pregnant adolescents and adult women. Arginine, citrulline, and NO kinetics were measured by i.v. infusions of (15)N(2)-argininine and (2)H(2)-citrulline in 8 adolescents and 8 adult women in the fasted state at the end of the first and the beginning of the 3rd trimesters of pregnancy. Arginine flux decreased (P < 0.05) from trimester 1 to 3 in the adolescents but not in the adult women. NO synthesis rate did not change significantly in either group from trimester 1 to 3. In trimester 3, there was a positive association (r = 0.55; P = 0.02) between arginine flux and participants' age, indicating that flux was slower in the younger participants. These findings suggest that after a brief period of food deprivation, the pregnant adolescent cannot maintain arginine production like her adult counterpart in late pregnancy. This inability to maintain arginine production seems to be related to her younger age. It does not, however, affect her ability to synthesize NO in late pregnancy.

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 2 H 2 -glycine and 15 N-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.Key words: Pregnant adolescent girls: Pregnant adult women: Glycine: Serine Pregnancy during adolescence in Jamaica and elsewhere is associated with a high prevalence of low birth weight (1,2) . It has been proposed that this is due to an inability of the adolescent mother to provide the nutrient needs for her own growth and the growth of her fetus. In particular, the requirement for amino acids increases as pregnancy progresses in order to sustain increased rates of protein deposition (3) and to support increased availability of glucose through gluconeogenesis (4) .Dispensable amino acids comprise the bulk of maternal amino acids transferred to the fetus in pregnancy (5) . A good example is glycine, which is a provider of methyl groups needed for the synthesis of DNA necessary for cell division to support maternal and fetal tissue deposition (6,7) . In addition, most of fetal cartilage is synthesised during late pregnancy and glycine constitutes 25 % of the amino acids in cartilage (8) . Therefore, as pregnancy progresses, there is a higher fetal demand for glycine. From our earlier study, glycine flux decreased by 39 % from the first trimester to the third trimester in pregnant adolescent girls (9) . Plasma glycine concentration in pregnant adolescent girls also decreased significantly from trimester 1 to 3, indicating a reduced availability. These findings suggested that after an overnight fast pregnant adolescent girls had a shortage in glycine supply in late pregnancy because they could not maintain production similar to their adult counterparts. However, de novo synthesis of g...

During pregnancy, adult women with a normal BMI synthesise extra amino acids after an overnight fast by increasing body protein breakdown and decreasing amino acid oxidation. It is not known whether adolescent girls can make these adaptations during pregnancy. The present study aimed to measure and compare the protein, glutamine and alanine kinetics of adult women and adolescent girls at early-, mid-and late-pregnancy. Kinetics were measured in the overnight fasted state using intravenous infusions of N 2 -urea in ten adults and eleven adolescents aged 16-17 years in the first and third trimesters (phase 2 study). In phase 1 study, there were no significant differences between the groups with regard to any of the kinetic parameters measured. In both groups, leucine flux increased (P,0·05), the percentage of leucine flux oxidised decreased (P,0·05) and non-oxidative leucine disposal to protein synthesis increased (P,0·05) from the first to the second trimester. In phase2 study, leucine flux was significantly slower (P,0·05) in the adult group than in the adolescent group during both trimesters, and whole-body leucine flux and non-oxidative leucine disposal increased significantly in the adolescent group (P,0·05, respectively) and were higher in the adult group from the first to the third trimester. These results suggest that similar to their adult counterparts after an overnight fast, adolescent girls with a normal BMI provide extra amino acids required for net protein deposition during pregnancy by increasing protein breakdown and decreasing amino acid oxidation.