Changes in serum albumin and alpha 1-acid glycoprotein concentrations during pregnancy: an analysis of fetal-maternal pairs.

The concentration of the two principal drug-binding proteins, albumin and alpha 1-acid glycoprotein, were measured in 44 paired fetal and maternal serum samples obtained at between 12 and 41 weeks gestation. Maternal serum albumin concentrations ranged between 25 and 35 g/l during this period. Fetal serum albumin was much lower in early gestation, ranging from 7.5 to 16 g/l at 12-15 weeks. With advancing age there was a linear increase so that at 30 weeks the fetal and the maternal serum albumin concentrations were in the same range and after 35 weeks the fetal concentrations exceeded the maternal by some 20%. Thus, the mean fetal/maternal serum concentration ratio of albumin increases from early pregnancy to term: 0.38 at 12-15 weeks; 0.66 at 16-25 weeks; 0.97 at 26-35 weeks; and 1.2 at greater than 35 weeks gestation. Maternal serum alpha 1-acid glycoprotein concentrations were scattered widely between 0.38 and 1.05 g/l. With the technique used fetal serum concentrations were hardly detectable before 16 weeks. Thereafter they increased at a constant rate, but never attained the maternal values. Near term a fetal/maternal serum concentration ratio of 0.37 was reached. These changes in protein concentrations may have important pharmacological implications.