High-risk pregnancy is associated with increased alpha-fetoprotein concentrations in the amniotic fluid and foal plasma

This study aimed to determine alpha-fetoprotein (AFP) concentrations in amniotic fluid, plasma of mares and respective foals: carrying normal pregnancies and delivering healthy foals (n=20; Group 1); carrying apparently normal pregnancies and delivering sick foals (n=15; Group 2); carrying high-risk pregnancies and delivering sick foals (n=14; Group 3). High-risk pregnancy was defined by a history of premature udder development/lactation or increased of the combined thickness of the uterus and placenta, or vulvar discharge and/or mares' systemic illness. Sick foals were affected by neonatal encephalopathy, sepsis, prematurity/dysmaturity, or hypoxic-ischemic encephalopathy. Based on histological examination of the chorioallantois, AFP trend was analyzed in pregnancies with pathologic (PFM) and normal fetal membranes (NFM). Concentrations of AFP were measured using a commercially available immunoassay previously validated for horses. Mares' plasma AFP did not change during the last 15-20 days of pregnancy in the three groups, and there was no difference among them. Amniotic fluid AFP was higher in Group 3 (p=0.014). Foals’ plasma AFP concentration was higher from birth to 72h in foals of Group 2 and 3 than in healthy ones, and foals of Group 3 had the highest value. The strong association (r=0.84; p<0.0001) between AFP in amniotic fluid and foals' plasma at birth is likely due to the presence of AFP in fetal urine. AFP was higher in pregnancy with PFM than with NFM in mare's plasma at admission (p=0.031), amniotic fluid (p=0.004), foal's plasma at birth (p=0.002), at 24 (p=0.005) and at 72 hours of life (p=0.004). AFP is higher in pregnancy with histopathological lesions of the chorioallantois providing the evidence of the differences between pregnancy with a normal placental barrier and the more compromised ones. The increased AFP concentration in the amniotic fluid and plasma of high-risk foals suggests upregulation.