How to estimate the amount of water
The volume of amniotic fluid increases until 34–36 weeks, and gradually decreases towards full term. Ultrasound uses two indicators. The amniotic fluid index is the sum of the depths of the pockets of water in the four parts of the uterus; a value of 5 cm or less is considered oligohydramnios. A simpler method is the deepest vertical pocket: less than 2 cm indicates oligohydramnios. One measurement may be inaccurate, so for borderline values the ultrasound is repeated.
- Amniotic fluid index 5 cm or less
- The depth of the largest pocket is less than 2 cm
- Early oligohydramnios - in the second trimester
- Later - in the third trimester and at full term
Reasons
In the second trimester, oligohydramnios is more often associated with defects of the fetal kidneys and urinary tract, rupture of the membranes, or severe placental insufficiency. In the third trimester, common causes are leakage of water, fetal growth restriction, preeclampsia and postmaturity. Some medications, such as nonsteroidal anti-inflammatory drugs in the second half of pregnancy and some blood pressure medications, reduce urine production by the fetus. Sometimes the reason cannot be found.
- Premature rupture of membranes
- Placental insufficiency, fetal growth restriction
- Preeclampsia, chronic hypertension
- Post-term pregnancy
- Malformations of the kidneys and urinary tract of the fetus
- Taking NSAIDs and some other medications
Why is oligohydramnios dangerous?
If there is little water from an early age, the child’s lungs may underdevelop and deformities of the limbs may develop due to compression. In the third trimester, oligohydramnios increases the risk of umbilical cord compression, especially during labor, changes in fetal heart rate, and cesarean section. The severity of the risks depends on the duration, degree of oligohydramnios and the cause, so there are no identical recommendations for everyone.
- Underdevelopment of the lungs with early severe oligohydramnios
- Umbilical cord compression
- Fetal heartbeat abnormalities during labor
- More frequent need for cesarean section
- Infection due to water leakage
Survey
First, leakage of water is ruled out: the doctor examines the woman and, if necessary, conducts a test for amniotic fluid. Expert ultrasound evaluates fetal anatomy, especially the kidneys and bladder, size and growth rate. Doppler measurement shows blood flow in the umbilical cord artery and fetal vessels, CTG shows the reaction of the child’s heartbeat. Mothers have their blood pressure taken and tests checked to rule out preeclampsia.
- Ultrasound with measurement of amniotic fluid index
- Expert ultrasound of fetal anatomy
- Doppler
- CTG
- Test for leakage of amniotic fluid
- Control of pressure and protein in urine
Tactics and treatment
Treatment is aimed at the cause and at a safe date for delivery. In case of isolated oligohydramnios without other disorders, the woman is observed with repeated ultrasound and CTG. Drinking enough can increase the amount of water for a short time, but it cannot replace observation. Medicines that can reduce the volume of water are canceled by the doctor. In case of water leakage and prematurity, hospitalization is carried out, infection and maturation of the fetal lungs are prevented. In case of full-term pregnancy and severe oligohydramnios, delivery is usually recommended.
- Repeated ultrasound and CTG
- Sufficient drinking regime
- Quitting NSAIDs without a doctor's prescription
- Hospitalization for water leakage
- Timely delivery
- Self-monitoring of fetal movements
