Maternal serum AFP test results report actual values and multiples of the median (MoM) by gestational age (in weeks). MoM are calculated by dividing the patient’s AFP by the midpoint (or median) of values expected for a large population of unaffected women at the same gestational age in weeks. MoM should be corrected for maternal weight. The MoM should also be corrected for maternal insulin requirement (achieved by dividing MoM by 1.1 for diabetic African American patients and by 0.8 for diabetic patients of other races) and multiple fetuses (multiply by 2.13 for twins). Some laboratories also provide additional statistical information regarding Down syndrome risk.

Increased In:

• Pregnant women:
  • Congenital nephrosis (related to defective renal reabsorption)
  • Fetal abdominal wall defects (related to release of AFP from open body wall defect)
  • Fetal distress
  • Fetal neural tube defects (e.g., anencephaly, spina bifida, myelomeningocele) (related to release of AFP from open body wall defect)
  • Low birth weight (related to inaccurate estimation of gestational age)
  • Multiple pregnancy (related to larger quantities from multiple fetuses)
  • Polycystic kidneys (related to defective renal reabsorption)
  • Underestimation of gestational age (related to the expectation of a lower value based on incorrect prediction of gestational age, i.e., AFP increases with age; therefore, if the age is believed to be less than it is actually, the expectation of the corresponding AFP value will be lower than it is actually, and the result appears to be elevated)
• Men, nonpregnant women, and children (the cancer cells contain undifferentiated hepatocytes that produce glycoproteins of fetal origin):
  • Cirrhosis
  • Hepatic carcinoma
  • Hepatitis
  • Metastatic lesions involving the liver

Decreased In:

• Pregnant women:
  • Down syndrome (trisomy 21)
  • Edwards’ syndrome (trisomy 18)
  • Fetal demise (undetected over a lengthy period of time) (related to cessation of AFP production)
  • Hydatidiform moles (partial mole may secrete some AFP)
  • Overestimation of gestational age (related to the expectation of a higher value based on incorrect prediction of gestational age; i.e., AFP increases with age; therefore, if the age is believed to be greater than it actually is, the expectation of the corresponding AFP value will be greater than it actually is, and the result appears to be decreased)
  • Pseudopregnancy (there is no fetus to produce AFP)
  • Spontaneous abortion (there is no fetus to produce AFP)