Maternal serum levels of alpha-fetoprotein and fetal fibronectin as markers of labor in the third trimester.

Unexplained elevations of maternal serum alpha-fetoprotein (MSAFP) in the second trimester have been found to be associated with a two- to fourfold increase in the rate of preterm delivery, but the sensitivity is low. Therefore, we reasoned that MSAFP levels in the third trimester could prove to be a more useful biochemical marker to predict labor. The presence of placental and membrane-derived fetal fibronectin (FFN) in cervicovaginal secretions has recently been shown to predict preterm delivery with a sensitivity of 81.7% and specificity of 82.5%. We postulated that damage to membranes and microscopic breakdown of fetomaternal blood barrier during labor might result in release of AFP or FFN into maternal serum. Maternal serum alpha fetoprotein and fetal fibronectin levels were measured prospectively in 29 patients in active labor at term and in 25 controls undergoing elective cesarean section. Neither MSAFP nor serum FFN levels were associated with labor at term. We did, however, note significantly higher MSAFP levels in mothers bearing male fetuses versus female fetuses (p < 0.01). Since the current literature supports a sex difference in the MSAFP levels in the second trimester, this does not appear to change as gestation advances. Further studies are needed to determine if, in addition to maternal weight and race, MSAFP levels should be also adjusted for fetal sex diagnosed on sonography.