The alpha-fetoprotein (AFP) is a protein produced by the liver and gastrointestinal tract of fetus and it is found in the maternal blood, in the fetal blood and in the amniotic liquid, where it reaches the maximum concentration at 14* -16* pregnancy week, then it decreases progressively; each pregnancy week has a specific AFP value.
The AFP detection on amniotic liquid, starting from the II trimester of pregnancy, is an indicator to highlight, before its time, defects of the fetal neural tube (anencephaly, spinal bifida). The AFP levels in the amniotic fluid increase when the neural tube isn't perfectly closed; but this increase could be observed in absence of malformations, so it is necessary making an accurate ecographic to control a fetal morphology. If a fetus has a trisomy 21 (Down syndrome), the AFP value is decreased.
When it is performed?
The optimal time for the alpha-fetoprotein dosage on the amniotic fluid is between 14^-16^ weeks.
The dosage results are available after 15 days from the draw blood.
If in the monochorial diamnotic pregnancies (monozygous twins) one of the twins is suffering from neural tube defects, the AFP value of not affectied twin may not be trusted because of it may be an AFP transfer among the twins. For dichorial diamniotic pregnancies (dizygous twins) there aren’t problems because of the AFP value are completely independent.