What is amniotic fluid index (AFI) and what does it mean?

The article was professionally consulted by Specialist Doctor I Le Hong Lien - Department of Obstetrics and Gynecology - Vinmec Central Park International General Hospital. Doctor Lien has over 10 years of experience as a radiologist in the Department of Ultrasound at the leading hospital in the field of obstetrics and gynecology in the South - Tu Du Hospital. And Master, Doctor Le Nhat Nguyen - Doctor of Obstetrics and Gynecology - Department of Obstetrics and Gynecology - Vinmec Danang International General Hospital. Doctor has more than 20 years of experience in the field of Obstetrics and Gynecology.

Amniotic fluid is the environment that helps protect and nourish the fetus during pregnancy. Any change in the amount of amniotic fluid can affect your baby's development. Amniotic fluid index AFI is an important parameter to help identify amniotic fluid abnormalities.

The fetus is surrounded by amniotic fluid. In addition to the task of protecting the fetus from external influences. Amniotic fluid helps the fetus maintain a stable temperature, water and electrolyte balance, is also a nutrient-rich environment, has the ability to regenerate and exchange, plays an important role in survival and fetal development while in the womb. Amniotic fluid appears from the 12th day after conception.
Amniotic fluid is made up of three sources: fetus, amniotic membrane and maternal blood.
Amniotic fluid reabsorption: It is done mainly through the fetal digestive system. From the 20th week of pregnancy, the fetus begins to swallow amniotic fluid. In addition, amniotic fluid is also reabsorbed through the fetal skin, the umbilical cord and the amniotic membrane. Thus, right from the beginning of pregnancy, amniotic fluid has the function of nourishing the embryo. After the placenta is formed, the amniotic fluid holds the metabolic fluid and other substances that ensure the survival and development of the fetus. After 34 weeks, the fetus absorbs 300-500ml of amniotic fluid per day. This amount of amniotic fluid into the intestine contributes to the formation of meconium, into the blood contributes to the balance of fluids in the fetus's body and is partially filtered to form urine for the baby.
Mechanically, amniotic fluid creates an environment for the fetus to develop harmoniously and to normalize the position of the fetus in the mother's genital tract in the last months of pregnancy. During labor, amniotic fluid continues to protect the fetus from the trauma of uterine contractions and infection. Amniotic fluid helps to establish the amniotic sac and dilates the mother's cervix, making it easier to clear the cervix. After the rupture of membranes, the oily nature of the amniotic fluid lubricates the mother's genital tract, making it easier for the fetus to be born. Amniotic fluid volume varies according to gestational age: at 8-12 weeks pregnant about 50ml, the maximum amniotic fluid volume is about 1000ml at 28 weeks gestation, then it gradually decreases to 900ml at 36 weeks gestation, at 40 weeks gestation. Amniotic fluid is about 600-800ml per week.

The main functions of amniotic fluid include:
A buffer to protect the fetus. Prevents adhesion of the amniotic membrane to the embryo. Air conditioning for the fetus. The place where the metabolic products of the embryo are stored. Promote embryo development.

Amniotic fluid index (AFI) is a measure of the amount of amniotic fluid present in a pregnant woman's abdomen at each stage of fetal development. Amniotic fluid index is measured when pregnant women visit the doctor, based on this index, the doctor will tell the mother whether the amount of amniotic fluid is normal or abnormal (polyhydramnios, oligohydramnios, amniotic fluid,...)
Measure only Amniotic fluid number AFI: Divide the uterine cavity into 4 parts, the two lines intersect at the belly button of the pregnant woman, measure the depth of the largest amniotic cavity in each chamber and calculate the sum of the above measurements.

For pregnancy, amniotic fluid plays an equally important role as the placenta, umbilical cord, and uterus in the role of nourishing and protecting the fetus. In addition to surveying the density and color of amniotic fluid, the amniotic fluid index (AFI) helps doctors predict and predict the health and development status of the baby still in the womb. Ultrasound to measure amniotic fluid index must be evaluated at least 2 consecutive times 2-6 hours apart to determine the status of oligohydramnios or amniotic fluid excess.

The table below will help pregnant women better understand how much AFI amniotic fluid index is normal and the notes that cannot be ignored if AFI is abnormal:

Each pregnant woman will have a different amount of amniotic fluid more or less depending on the time of pregnancy and the amount of water entering the body each day. In order for the fetus to be fully developed and born healthy, the mother must also maintain a stable and normal amount of amniotic fluid, avoiding excess or lack of amniotic fluid.
Therefore, mothers need to have adequate nutrition, reasonable rest, drink enough water every day, have regular antenatal check-ups, do prenatal screening tests as prescribed by the doctor; When there are signs of polyhydramnios or oligohydramnios, it is necessary to closely monitor and treat promptly.