Low Amniotic Fluid (Oligohydramnios) During Pregnancy

Maintaining a healthy level of amniotic fluid during pregnancy is largely out of anyone’s control.  During pregnancy, if the amniotic fluid volume falls below a certain threshold, this can present a risk factor to the developing fetus. This occurrence is called oligohydramnios which refers to abnormally low amniotic fluid levels.

The amniotic fluid is produced by the fetus and acts as a protective layer to grow optimally. Thus, in such cases when oligohydramnios occurs, there’s a risk of several complications for both mother and child. Here we go into more details for expecting mothers to know what to look out for should these levels begin to drop too much.

Amniotic Fluid and Proper Levels

Amniotic fluid plays a vital role in baby’s well-being during the fetal stage. As the fluid circulates around the fetus and is swallowed and released as the fetus grows. This constant circulation and presence help with movement and proper growth, prevents pressure on the umbilical cord, and maintains a constant temperature for the fetus. This fluid that surrounds the fetus in the uterus also provides protection from external movements and pressure, and cushions the fetus as it grows.

As the fetus develops, so does the production of amniotic fluid as it collects in the amniotic sac. This fluid is produced by the fetus and is typically clear or slightly yellowish in color. Fluid volume in the amniotic sac can be assessed by how far up the abdominal wall it is present.

The level of amniotic fluid varies throughout pregnancy, reaching its greatest amount at about 34-weeks gestation. Fluid levels are established using an amniotic fluid level index, stating that 5 cm to 25cm is an acceptable range. Less than 5 cm is considered oligohydramnios, while an amniotic fluid level that is greater than 25 cm is considered polyhydramnios.

If at any point there is less than 5 cm of fluid or more than 25 cm of fluid, it can indicate a problem in the baby’s development.

These low levels of amniotic fluid, or oligohydramnios, occur in about four percent of pregnancies. While this condition can occur at any stage during pregnancy, it is most common in the last trimester, and occurs in about 12 percent of pregnancies that extend beyond two weeks past their due dates.

Signs of Oligohydramnios

Typically, the onset of oligohydramnios itself does not cause recognizable maternal symptoms other than a sense of decreased fetal movement. For the mother, uterine size may be less than necessary based on gestational age, but ultimately it won’t be until a prenatal screening that something is detected early on. That being said, disorders that may cause or contribute to the onset of oligohydramnios may present symptoms, but the condition itself is mostly unnoticeable by the mother.

When prenatal screenings do occur, an ultrasound and physical exam may be performed to check for signs that oligohydramnios has occurred. Additionally, fetal screenings during labor will also indicate levels and determine signs of low amniotic fluid levels. These signs include;

Causes and Risk Factors

Amniotic fluid is naturally occurring during pregnancy, however a low fluid levels can occur for a number of reasons.

The major cause of low amniotic fluid is a problem with the fetus’ kidneys or its urinary tract.

In cases where the fetus is not producing enough urine, it cannot produce adequate levels of amniotic fluid. Additionally, in these cases it is also possible that the fetus cannot transfer the fluid from its kidneys to its bladder properly. In which case, the fluid builds up in the kidneys rather than being transferred and expressed from the bladder.

Additional risk factors and causes include;

• Birth defects involving the kidneys or urinary tract.
• Maternal and gestational diabetes, which can affect neonatal growth and weight.
• Placental problems, in which the placenta is not providing adequate supply of blood and nutrients to the fetus.
• Hypertension or preeclampsia.
• Leaking or ruptured of membranes, also known as premature rupture of membranes (PROM), in which the amniotic sac breaks or begins to leak fluid.
• Dehydration.
• Extended pregnancy more than two weeks beyond the due date.

Concerns, Complications and Treatment

When the amniotic fluid levels are inadequate, there are several risks for the mother and the baby . These include:

• Premature birth – Premature birth occurs when a baby is born before 37 weeks. If the fetus does not have enough fluid, it may be born before the due date.
• Fetal growth restriction – Fetal growth restriction, in which the baby does not grow as much as it should. This can lead to problems after birth, such as low blood sugar, blood pressure and a low oxygen level in the baby’s blood.
• Fetal death – If the fetus does not have enough fluid and the situation cannot be remedied quickly, it will be unable to grow and develop properly, which, depending on the stage of pregnancy may result in fetal death.

An oligohydramnios diagnosis can be a potentially fatal condition if not treated, as well as a possibility for leading to significant complications in the baby’s growth and make childbirth more complicated.

When a diagnosis occurs, in addition to managing the underlying cause, weekly monitoring will be recommended to measure fluid levels and fetal health via measurements and nonstress tests, which have demonstrated to decrease the occurrence of unexplained fetal death. Additionally, maternal hydration will play a vital role in treatment, particularly in cases of isolated oligohydramnios in the third trimester.

Amnioinfusion may be administered in some cases to inject a saline solution, which is a salty water mixture, into the uterus via the cervix to increase fluid levels in the amniotic sac. In cases where fluid levels get too low or if the baby is unable to stay healthy internally, a doctor may recommend inducing labor for early delivery to prevent problems during labor and birth.

Although there is some controversy surrounding the timing of delivery in cases of isolated oligohydramnios, the current recommendations support delivery at 37 weeks’ gestation, assuming membranes remain intact.

Additionally, there are tests that can be performed to determine whether the baby has a kidney or urinary tract problem, and doctors may recommend treatment before labor and delivery if other conditions are contributing to oligohydramnios, such as a high-risk pregnancy. Doctors may also recommend less physical activity or going on bed rest for the remainder of the pregnancy.

The care of patients and treatment for low amniotic fluid relies on coordination among several medical providers to ensure adequate screening, diagnosis, and management is in place. Early detection of oligohydramnios during routine prenatal care visits is possible and thus, maintaining regular prenatal screenings is essential for early diagnosis and treatment.

If at any point a mother has concern for amniotic fluid levels, consultation with a doctor or specialist is important.