Relationship between some obstetric landmarks and the concentration of alpha-fetoprotein in maternal blood

Alpha-fetoprotein (AFP) quantitation in maternal blood has been used for prenatal diagnosis of anencephaly, spina bifida and some other congenital abnormalities. The levels of AFP in pregnancy serum are greatly dispersed within each gestational period, what makes the test of difficult interpretation mainly in border line cases. The factors which contribute to this variability are still poorly understood. They must act either on the synthesis or catabolism of the protein, or on the permeability of the fetal-maternal barrier. In an attempt to elucidate some of these factors, the levels of AFP in serum of 89 women at 32 to 34 weeks gestation and of 115 women at term were measured by radioimmunoassay and related to several obstetric variables such as parity, pregnancy number, 1 - minute Apgar score, smoking habit and sex of newborn. It was seen that parity and pregnancy number do not correlate with the levels of AFP in pregnancy serum. Smokers, particularly those who smoke more than a pack per day, however, had higher levels of the protein in their blood. The interpretation of these data should take into consideration the fact that smoking causes vasoconstriction and important vascular alterations similar to the ones encountered in diabetic angiopathy. It is possible that an increased microvascular permeability of placenta and/or membranes to proteins of the size of AFP from the fetus to maternal circulation may explain the greater levels of the protein in serum of smokers.(ABSTRACT TRUNCATED AT 250 WORDS)