Amniotic Fluid Volume Affects Fetal Growth and Development
The colorless, transparent fluid surrounding the baby in the uterus is called amniotic fluid. It protects the fetus from external impacts, participates in fetal metabolism, and cushions the mother by reducing discomfort from fetal movements.During a normal pregnancy, amniotic fluid volume gradually increases with gestational age, typically reaching approximately 1000 milliliters by 38 weeks and around 800 milliliters at term.
Both excessive and insufficient amniotic fluid constitute abnormal conditions requiring significant attention from expectant mothers.Polyhydramnios Any amniotic fluid volume exceeding 2000 milliliters during pregnancy is classified as polyhydramnios, with the highest recorded cases reaching up to 2000 milliliters. Mothers with polyhydramnios may experience shortness of breath, upper abdominal discomfort, an enlarged uterus relative to gestational age, shiny and swollen abdominal skin due to overstretched tissue, weak fetal movements, and distant fetal heart sounds.An amniotic fluid index exceeding 18 cm on ultrasound indicates polyhydramnios.
Causes of Polyhydramnios
Fetal Anomalies: Approximately 18%–40% of polyhydramnios cases involve fetal abnormalities, most commonly neural tube defects such as anencephaly, encephalocele, and spina bifida, accounting for about half of these cases.
Multiple pregnancies: Monozygotic twins are more common. If twin-to-twin transfusion syndrome occurs, the larger twin is more likely to develop polyhydramnios. Pregnant women with conditions such as diabetes, hepatitis, gestational hypertension, or blood type incompatibility.
Fetal placental or umbilical cord abnormalities: Such as velamentous umbilical cord insertion or chorioamnionitis.
Idiopathic polyhydramnios: Occurs without any warning signs, fetal or placental abnormalities, and the cause remains unknown.
Oligohydramnios
Total amniotic fluid volume less than 300 milliliters in late pregnancy.In cases of oligohydramnios, the amniotic fluid appears viscous, cloudy, and dark green. The expectant mother's abdomen becomes highly sensitive and prone to contractions. During prenatal checkups, both fundal height and abdominal circumference measure smaller than those of mothers at the same gestational age, and fetal movement within the uterus is restricted. An ultrasound revealing an amniotic fluid index (AFI) less than 8 cm indicates oligohydramnios.Oligohydramnios carries significant risks during pregnancy, including increased likelihood of intrauterine fetal death, fetal distress during labor, heightened surgical complexity, and severe challenges in postnatal care. Consequently, it warrants high priority attention from obstetricians. Causes of Oligohydramnios Fetal Anomalies: Often associated with congenital urinary tract abnormalities leading to oliguria or anuria in the fetus, resulting in reduced amniotic fluid.
Post-term pregnancy: Toward the end of pregnancy, placental aging causes amniotic fluid volume to gradually decrease.
Fetal growth restriction: Occasionally, oligohydramnios results from intrauterine growth restriction. The baby may not exhibit abnormalities but grows more slowly than other fetuses at the same gestational age. This is generally associated with maternal malnutrition or viral infections.