Alpha Fetoprotein – AFP Maternal, (Maternal Serum AFP , α1- Fetoprotein )
- Pregnant mother serum is needed. It is stable for 24 hours at 2 to 8 °C.
- Take 3 to 5 ml of blood in the disposable syringe.
- Keep the syringe for 15 to 30 minutes and then centrifuge for 2 to 4 minutes. In this way can get a clear serum.
- Keep serum at 2 to 8 °C if the test is performed within 24 hours, otherwise, freeze it at -20 °C.
- This is an effective screening marker for the diagnosis of body wall defects in the fetus like neural tube defect, spina bifida, or anencephaly.
- This test is indicated in the pregnant ladies who have the following findings:
- Female over the age of 35 years.
- If there is a family history of birth defects.
- If the lady has taken harmful medications during pregnancy.
- Female with a history of diabetes mellitus.
- AFP (α1- Fetoprotein) has 40% carbohydrates with a molecular mass of 70 kD. This is also called as α1- Fetoprotein.
- AFP is an oncofetal protein ( glycoprotein ) synthesized in the fetal liver and yolk sac.
- Some of the fetal AFP enters the maternal serum (circulation).
- AFP is the dominant fetal serum protein in the first trimester.
- It is very low at the age of one year.
- Maternal AFP rises progressively in the first and second trimesters.
- Maternal serum reaches its peak at the 13th week of gestation, then declines rapidly to <2% of the maximum level by 34 to 36 weeks of pregnancy.
- Amniotic AFP is more accurate to diagnose neural tube defects in the early gestation (around 14 weeks) than maternal serum AFP.
- Neural tubes defect varies from small myelomeningocele to anencephaly.
- Other fetal body wall defects are:
- The AFP at 8th week is very high, then there is a dip at 11 weeks and again peak at 13 weeks. Then fall in long-linear fashion till 25 weeks.
- Before 14 weeks AFP helps to diagnose neural tube defects.
- Normal AFP <2.5 Multiples of median (MoM).
- For the neural tube, the defect is >2.5 MoM.
- If there is a body wall defect in the fetus then AFP leaks out into amniotic fluid and picked up by the maternal circulation.
- If there is an increased level of AFP then further evaluated by repeated AFP, amniotic fluid AFP, and ultrasound.
- The serum AFP level is 100 times of that amniotic fluid.
|Maternal serum level AFP|
|14 weeks of gestation||25.6 ng/mL (median)|
|16 weeks of gestation||34.8 ng/mL (median)|
|18 weeks of gestation||47.3 ng/mL (median)|
|20 weeks of gestation||64.3 ng/mL (median)|
|21 weeks of gestation||74.9 ng/mL (median)|
|Fetal serum level AFP|
|First-trimester peak||200 to 400 mg/dL|
|later on, fall 1% of the peak|
|Cord blood||<5 mg/dL|
|97% of the healthy population||<8.5 ng/dL|
|100% of the healthy population||<15.0 ng/dL|
- Adult = <40 ng/mL (<40 mcg/L)
- Child (<1 year) = <30 ng/mL
Raised AFP level seen in:
- Maternal serum level >2 times the median level will be seen in:
- Multiple gestations.
- Fetal death.
- Malformations e.g. anencephaly.
- Increased AFP concentration in maternal serum and amniotic fluid is seen in:
- open neural tube defects like anencephaly, spina bifida, omphalocele, esophageal or duodenal atresia.
- Threatened abortion.
- Fetal distress.
- Intrauterine death of the fetus.
- Fetal congenital abnormalities.
- Abdominal wall defects like gastroschisis.
Other conditions are:
- Renal abnormalities
- Cystic hygroma.
- Hydrops fetalis.
- Turner syndrome.
- Bowel obstruction.
- Feto-maternal hemorrhage.
- Sacrococcygeal Teratoma.
Decreased maternal serum AFP is seen in:
- Down syndrome (Trisomy 21).
- Molar pregnancy.
- Spontaneous abortion.
- overestimated gestational age.
Low level of AFP with an abnormal value of HCG and estriol (Triple screening) is indicative of :
- Trisomy 21 (Down’s syndrome).
- Trisomy 18 (Edwards syndrome)
- Or other chromosomal abnormalities.