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Introduction ⬇

AFP is a protein produced by the fetal liver and is present in amniotic fluid, with small amounts crossing the placenta into the maternal bloodstream. The measurement of MSAFP is performed to screen for fetal abnormalities and neural tube defects and is offered between 15 and 21 weeks’ gestation when AFP concentration rises dramatically. Approximately 90% of infants with neural tube defects are born to parents who have no recognized risk factors for the disorder. Maternal quad screening aids in identifying Down syndrome risk. The test also detects complications of pregnancy, and AFP serves as a tumor marker in nonpregnant women. This test is also used to detect pregnancy complications such as fetal growth restriction, fetal distress, and fetal demise. It can also be used to diagnose and monitor hepatocellular, testicular, ovarian, and malignant liver diseases.

Procedure ⬆ ⬇

  1. Obtain a 10-mL venous blood sample (red-topped tube). Observe standard precautions. Label specimen with the patient’s name, date, and test(s) ordered and place specimen in a biohazard bag.

  2. Plan the first screening at 15–18 weeks. If the result is normal, no further screening is necessary. If AFP level is low, consider ultrasound studies to determine exact fetal age. A second screening may be done after an initial elevated AFP level. If the result is normal, no further screening is necessary.

Clinical Implications ⬆ ⬇

Abnormal levels should be followed by ultrasound and amniocentesis.

  1. Elevated MSAFP level can indicate:

    1. Neural tube defects of spina bifida (a vertebral gap) or anencephaly (>2.5 MoM)

    2. Underestimation of gestational age

    3. Multiple gestation (>4.5 MoM)

    4. Threatened miscarriage

    5. Other congenital abnormalities

  2. Elevated MSAFP level early in pregnancy is associated with:

    1. Congenital nephrosis

    2. Duodenal atresia

    3. Umbilical hernia or protrusion

    4. Sacrococcygeal teratoma

  3. Elevated MSAFP level in the third trimester is associated with:

    1. Esophageal atresia

    2. Fetal teratoma

    3. Hydranencephaly

    4. Rh isoimmunization

    5. Gastrointestinal tract obstruction

  4. Low MSAFP level is associated with:

    1. Long-standing fetal death

    2. Down syndrome (trisomy 21)

    3. Other chromosome abnormalities (trisomy 13, trisomy 18)

    4. Hydatidiform mole

    5. Pseudopregnancy

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain the reason for testing the patient’s blood.

  2. Determine the gestational age from the last menstrual period. If the last menstrual period is not known, determine gestational age with ultrasound.

  3. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Collaborate with the healthcare provider to interpret the outcome and counsel the patient about the results.

  2. Explain the possible need for further testing.

    1. Elevated maternal AFP levels should be followed by a second screening or ultrasound studies for fetal age.

    2. Low maternal AFP levels should be followed by ultrasound studies and then by amniocentesis.

  3. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆ ⬇

  1. Obesity causes low AFP levels.

  2. Race is a factor: AFP levels are 10%–15% higher in Black people and are lower in Asian people than in White people.

  3. Insulin-dependent diabetes results in low AFP levels.

Clinical Alert

If the MSAFP level is elevated and no fetal defect is demonstrated (i.e., by ultrasound or amniocentesis), then the pregnancy is at an increased risk (e.g., premature birth, low-birth-weight infant, fetal death)

Reference Values ⬆

Normal