Amniotic Fluid Index and Normal Amniotic Fluid Index (AFI) Chart During Pregnancy
Amniotic Fluid Index is one of the 5 components of biophysical profile, which also also know as a prenatal ultrasound. Biophysical profile helps in evaluation of the fetal well-being. Prenatal ultrasound can predict pregnancy outcome. Abnormal value of AFI may result into fetal and maternal disorders.
Components other than Amniotic Fluid Index Involved In Prenatal Ultrasound
1.Fetal heart rate
2.Fetal breathing
3. Fetal movement
4. Fetal tone
Amniotic fluid (AF) is a complex substance which is essential to fetal well-being. It is a fetal urine or protective liquid present in the amniotic sac of a pregnant uterus. It develops as a fluid filled with extracelomic void near the time of establishment of embryo and in some cases even before the embryo is recognized.
The AFI is a standardized way to assess the sufficiency of amniotic fluid quantity in pregnancy. This amniotic fluid index is using for patients who are at least 24 weeks pregnant with a singleton gestation.
Amniotic fluid is not only including diagnostic function but also comprise nutritive, protective function.
This AFI is play a significant role in fetal well-being and its abnormality may cause fetal death. Amniotic Fluid Index is abnormal, when the AF volume may be more or less than expected.
AFI is the score which is assess in “cm” which means the amount of amniotic fluid observed on ultrasound of a pregnant uterus.
Normal range of Amniotic Fluid Index is considered between 8-18 cm.
Median Amniotic Fluid Index level is approximately 14 cm from week 20 to week 35, when the amniotic fluid starts to decrease in preparation for birth.
Type of Abnormalities and Amniotic Fluid Index Range
Anhydramnios : A case of virtually no fluid in the amniotic sac.
Oligohydramnios : The Amniotic Fluid volume is less than expected range. An AFI is <5-6 cm. The exact number can vary by gestational age. The fifth percentile for gestational age is sometimes used as a cutoff value.
Polyhydramnios : occurs as a result of either increased production or decreased removal of AF. An Amniotic Fluid Index is >24-25 cm.
Amniotic Fluid volume is a function of the fetal gestational age, where the amount of fluid moves to the gestation across the placental membrane and the fluidity of water across the amnion along with the openness of the Amniotic Fluid membrane and presence or absence of fetal anomalies.
Water in the Amniotic Fluid originally comes from the maternal plasma and passes through the fetal membranes based on hydrostatic and osmotic forces. When placenta and fetal vessels develop, water and solute from maternal plasma pass across the placenta to the fetus and then to the Amniotic Fluid.
Amniotic Fluid exchange is through a bi-directional circulation between the fetus and the AF across the fetal skin, the surface of the amnion, placenta, and the umbilical cord before keratinization. Swallowing and urination through the urethra dominate after keratinization of the fetal skin and patency of the urethra.
The amount of Amniotic Fluid in the amniotic sac can be assessed non-invasively by use of ultrasound.
Amniotic Fluid low Reasons
Birth defects
It may occur if the fetus has difficulties with the growth of the kidneys or urinary tract, which may cause reduction in urine production, and in turn decreases the levels of AFI.
Breakage of membranes
Breakage of membranes may be cause by a stream of fluid or a slow constant drip of fluid. This is happen due to a tear in the membrane and premature rupture of membranes can also be a reason of low AFI.
Mother Health Ailment
Mother’s with diseases like diabetes, dehydration, preeclampsia, and chronic hypoxia may produce effect on AFI levels.
Placental problems
When placenta is not providing enough blood and nutrients to the baby, then the baby may stop recycling fluid and which causes low AFI.
Disclaimer :This article is only for the information of readers.
References/ Sources of Information are:
ncbi.nlm.nih.gov, pubmed.ncbi.nlm.nih.gov, wikipedia.org