Oligohydramnios 

Overview: 

Oligohydramnios is the condition of having too little amniotic fluid.  Doctors can measure the amount of fluid through a few different methods, most commonly through amniotic fluid index (AFI) evaluation or deep pocket measurements. If an AFI shows a fluid level of less than 5 centimeters (or less than the 5th percentile), the absence of a fluid pocket 2-3 cm. in depth, or a fluid volume of less than 500mL at 32-36 week’s gestation, then a diagnosis of oligohydramnios would be suspected. 

About 8% of pregnant women can have low levels of amniotic fluid, with about 4% being diagnosed with oligohydramnios. It can occur at any time during pregnancy, but it is most common during the last trimester.  If a woman is past her due date by two weeks or more, she may be at risk for low amniotic fluid levels since fluids can decrease by half once she reaches 42 weeks (about 9 and a half months) gestation. Oligohydramnios can cause complications in about 12% of pregnancies that go past 41 weeks. 

1. Causes: 

a. Birth defects – Problems with the development of the kidneys or urinary tract which could cause little urine production, leading to low levels of amniotic fluid. 

b. Placental problems – If the placenta is not providing enough blood and nutrients to the baby, then the baby may stop recycling fluid. 

c. Leaking or rupture of membranes –This may be a gush of fluid or a slow constant trickle of fluid. This is due to a tear in the membrane. Premature rupture of membranes (PROM) can also result in low amniotic fluid levels. 

d. Post Date Pregnancy– A postdate pregnancy (one that goes over 42 weeks) can have low levels of amniotic fluid, which could be a result of declining placental function. 

e. Maternal Complications– Factors such as maternal dehydration, hypertension, preeclampsia, diabetes, and chronic hypoxia can have an effect on amniotic fluid levels. 

2. Risks: 

If oligohydramnios is detected in the first half of pregnancy, the complications can be more serious and include: 

• Compression of fetal organs resulting in birth defects. 

• Increased chance of miscarriage or stillbirth. 

If oligohydramnios is detected in the second half of pregnancy, complications can include: 

• Intrauterine Growth Restriction (IUGR). 

• Preterm birth. 

• Labor complications such as cord compression, meconium-stained fluid and cesarean delivery. 

The risks associated with oligohydramnios often depend on the gestation of the pregnancy. The amniotic fluid is essential for the development of muscles, limbs, lungs, and the digestive system. In the second trimester, the baby begins to breathe and swallow the fluid to help their lungs grow and mature. The amniotic fluid also helps the baby develop muscles and limbs by providing plenty of room to move around. 

3. Treatment: 

The treatment for low levels of amniotic fluid is based on gestational age. If you are not full term yet, your doctor will monitor you and your levels very closely. Tests such as non-stress and contraction stress tests may be done to monitor your baby’s activity. If you are close to full term, then delivery is usually what most doctors recommend in situations of low amniotic fluid levels. 

Other treatments that may be used include: 

• Amnio-infusion during labor through an intrauterine catheter.  This added fluid helps with padding around the umbilical cord during delivery and is reported to help lower the chances of a cesarean delivery. 

• Injection of fluid prior to delivery through amniocentesis.  The condition of oligohydramnios is reported to often return within one week of this procedure, but it can aid in helping doctors visualize fetal anatomy and make a diagnosis. 

• Maternal re-hydration with oral fluids or IV fluids has been shown to help increase amniotic fluid levels. 

4. Prognosis: 

• The earlier in pregnancy that oligohydramnios occurs, the poorer the prognosis. Fetal mortality rates as high as 80-90% have been reported with oligohydramnios diagnosed in the second trimester. Most of this mortality is a result of major congenital malformations and pulmonary hypoplasia secondary to PROM before 22 weeks of gestation. Mid-trimester PROM often leads to pulmonary hypoplasia, fetal compression syndrome and amniotic band syndrome. The inspiration of amniotic fluid at regular intervals is probably needed for terminal alveolar development 

• The assessment of AFV is important in pregnancies complicated by abnormal fetal growth or intrauterine growth restriction. Oligohydramnios is a frequent finding in pregnancies involving intrauterine growth restriction and is most likely secondary to decreased fetal blood volume, renal blood flow and subsequently fetal urine output. Pregnancies complicated by severe oligohydramnios have been shown to be at increased risk of fetal morbidity. 

5. Complications: 

• Pulmonary hypoplasia. 

• Fetal compression syndrome. 

• Amniotic band syndrome. 

• The risk of fetal infection is increased (by the presence of prolonged ROM). 

Why is Oligohydamnios important to the NICU RT?

• Increased Risk of Respiratory Distress: Infants born with oligohydramnios are more likely to have underdeveloped lungs, which can lead to RDS or the need for surfactant therapy.

• Meconium Aspiration: With reduced amniotic fluid, there is a higher chance that the fetus may pass meconium in utero, which can lead to meconium aspiration syndrome (MAS) at birth. MAS can cause airway obstruction and significant respiratory distress.

• Pulmonary Hypoplasia: In severe cases, oligohydramnios can contribute to underdeveloped or small lungs, a condition called pulmonary hypoplasia, which leads to compromised ventilation and oxygenation.