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Amniotic fluid index (AFI) is a quantitative estimate of amniotic fluid [1] and an indicator of fetal well-being. It is a separate measurement from the biophysical profile. [1] AFI is the score (expressed in centimetres) given to the amount of amniotic fluid seen on ultrasonography of a pregnant uterus.
The amniotic fluid is the protective liquid contained by the amniotic sac of a gravid amniote. This fluid serves as a cushion for the growing fetus, but also serves to facilitate the exchange of nutrients, water, and biochemical products between mother and fetus. For humans, the amniotic fluid is commonly called water or waters (Latin liquor ...
Usual follow-up steps include (1) a prenatal ultrasound exam to look for fetal abnormalities and/or (2) measurement of AFP in amniotic fluid obtained via amniocentesis. Maternal serum AFP (MSAFP) varies by orders of magnitude during the course of a normal pregnancy. MSAFP increases rapidly until about 32 weeks gestation, then decreases gradually.
The presence of these biophysical variables implies absence of significant central nervous system hypoxemia/acidemia at the time of testing. By comparison, a compromised fetus typically exhibits loss of accelerations of the fetal heart rate (FHR), decreased body movement and breathing, hypotonia, and, less acutely, decreased amniotic fluid volume.
The volume of amniotic fluid typically increases until 36 weeks and starts decreasing after 40 weeks in post-term gestations. [4] For this reason, discrepancies between fundal height measurements and gestational age can be a clinical indication of amniotic fluid abnormality and should be evaluated by ultrasound.
Polyhydramnios is a medical condition describing an excess of amniotic fluid in the amniotic sac.It is seen in about 1% of pregnancies. [1] [2] [3] It is typically diagnosed when the amniotic fluid index (AFI) is greater than 24 cm. [4] [5] There are two clinical varieties of polyhydramnios: chronic polyhydramnios where excess amniotic fluid accumulates gradually, and acute polyhydramnios ...
The lecithin–sphingomyelin ratio is a marker of fetal lung maturity. The outward flow of pulmonary secretions from the fetal lungs into the amniotic fluid maintains the level of lecithin and sphingomyelin equally until 32–33 weeks gestation, when the lecithin concentration begins to increase significantly while sphingomyelin remains nearly the same.
Measurement of AFP is generally used in two clinical contexts. First, it is measured in pregnant women through the analysis of maternal blood or amniotic fluid as a screening test for certain developmental abnormalities, such as aneuploidy .