[Free amino acids in the amniotic fluid and maternal plasma in different periods of the normal pregnancy]. / Concentración de aminoácidos libres en líquido amniótico y en plasma materno en diferentes etapas del embarazo.

ABSTRACT

OBJECTIVE: To describe changes in the concentration of total free amino acids (TFAA) in amniotic fluid (AF) and in maternal plasma (MP) at different periods of pregnancy, to analyze their differences, and to correlate the composition of the aminograms (AMG). METHODS: A total of 19 free AA. were measured by chromatography in the AF and MP from 18 women with uncomplicated singleton pregnancies, 6 at 16 weeks of gestation (wg), 6 at 28 wg and, 6 at 36 wg. Differences in the TFAA concentration at each gestational age, essential/non-essential, and polar/non-polar AA ratios were calculated. The correlation between the AMG in AF and in MP at each gestational age, was also estimated. RESULTS: In the AF there was a reduction in the concentration of TFAA throughout pregnancy (p = 0.023) whereas, in MP the TFAA concentration did not change. TFAA concentration was lower in AF than in MP at 36 weeks of gestation (p = 0.001). The composition of the AMG in MP did not change during pregnancy with a correlation coefficient between 16 and 28 wg of r = 0.98 (95% confidence interval [95%CI] 0.94-0.99), between 16 and 36 wg r = 0.95 (95% CI 0.86-0.99) and between 28 and 36 wg r = 0.93 (95% CI 0.82-0.97). The ratio of essential/non-essential and polar/non-polar AA was also unchanged. In AF, the composition of the AMG changed during pregnancy with a correlation between 16 and 28 wg r = 0.83 (95% CI 0.59-0.93), and between 16 and 36 wg r = 0.78 (95% CI 0.49-0.91). This was due to a reduction in the basic AA and an increment in the acid and neutral AA. The correlation between the AMG in AF and in MP at 16 wg was r = 0.94 (95% CI 0.84-0.96), at 28 wg r = 0.82 (95% CI 0.57-0.92) and, at 36 wg r = 0.71 (95% CI 95% 0.37-0.88). CONCLUSION: During pregnancy, TFAA and the AMG in MP remained stable. In AF, TFAA were reduced and the AMG changed towards the end of the pregnancy.