Oligohydramnios

Definition
During pregnancy, your baby is surrounded in the womb by amniotic fluid. This fluid, which is produced by the placenta and your baby, provides a cushioned environment at the right temperature and allows room for your baby to grow and move. A deficiency in the amount of amniotic fluid is called oligohydramnios, a condition that can occur in up to 8 percent of pregnancies.

Causes/associated factors
What causes oligohydramnios is not completely understood. It has been associated with various conditions, however, including:
fetal birth defects, such as urinary tract defects (which obstruct the normal flow of urine into the amniotic fluid) and chromosome defects (which occur in about 7 percent of cases)
medications taken by the mother, including certain medications for hypertension (angiotensin-converting enzyme inhibitors, such as captopril and enalapril) and nonsteroidal anti-inflammatory medications (such as ibuprofen, indomethacin and sulindac)
pregnancy complications, including hypertension, preeclampsia, diabetes and lupus
placental insufficiency (when the placenta cannot provide an adequate supply of nutrients or oxygen to the fetus)
placental abruption (a complication caused by the accumulation of blood between the placenta and the wall of the uterus)
inadequate fetal growth
leaking membranes or premature rupture of the membranes (The amniotic sac typically breaks as part of the labor process. If your water breaks before labor begins, it's called premature rupture of the membranes.)
uterine infection
fetal stress
pregnancy that continues past 40 weeks
Oligohydramnios can also occur when no risk factors are present.


Signs/symptoms
Symptoms associated with oligohydramnios are not well defined. Your doctor may suspect oligohydramnios based on the findings of a physical exam or the presence of certain risk factors. The condition may also be found during a routine ultrasound (a procedure in which sound waves are used to create an image of your baby and the surrounding organs), when a decrease in the volume of amniotic fluid may be noted.

Diagnosis
An ultrasound is used to measure the volume of amniotic fluid. An experienced clinician can often estimate the amount of fluid present in the amniotic sac. If a more accurate measurement is needed, he or she may use the amniotic fluid index or the maximum vertical pocket -- measurements of the fluid pockets surrounding your baby.
Amniotic fluid index (AFI): Determining the amniotic fluid index depends on how long you've been pregnant. If you're less than 20 weeks pregnant, the diameters of the largest fluid pocket on the right side of your uterus and the largest pocket on the left are added together to determine the AFI. If you're more than 20 weeks pregnant, the uterus is divided into four equal parts and the diameters of the largest pocket in each section are added together. Normal AFI varies with gestational age. After 30 weeks, it's usually between 8 and 24 centimeters. Oligohydramnios is diagnosed when the AFI is 5 or less.

Maximum vertical pocket (MVP): To determine maximum vertical pocket, the depth of the largest fluid pocket that doesn't contain any fetal body parts or umbilical cord is measured. The amniotic fluid volume is considered normal if the largest pocket is bigger than 2 centimeters. Oligohydramnios is diagnosed when no pocket is bigger than 2 centimeters.

Once the diagnosis is made, an ultrasound and other tests may be used to help the doctor determine if birth defects or other conditions associated with oligohydramnios are present.


Treatment
The goal of treatment is to maintain your pregnancy until your baby's lungs are mature enough for life outside the womb. In some cases, no treatment is necessary. If your baby is not yet mature enough for delivery, your doctor may simply choose to closely monitor your health and your baby's health. Regular testing may begin as early as 26 weeks of pregnancy, including the following:
Nonstress test: This test uses an ultrasound to measure the response of your baby's heart rate to its movements within the uterus. Normally, the baby's heart rate increases in response to movement. Ideally, the baby's heart rate will speed up for a brief time in response to movement at least twice during a 20-minute period. This is known as a "reactive" nonstress test.

Biophysical profile: This test includes an ultrasound to assess the amniotic fluid volume, fetal movement, fetal tone and fetal breathing, as well as a nonstress test to measure the fetal heart rate acceleration. Each variable is given a score of 2 for normal or 0 for abnormal. A total score of 8 or more is considered normal. A score of 6 is considered suspicious. In this case, your doctor will do further testing if you're preterm or may suggest delivery if you're at term. A score of 4 or less indicates that the baby is probably stressed. In this case, you will be hospitalized and an early delivery may be necessary.

Modified biophysical profile: This includes only the amniotic fluid index and nonstress test.

Fetal movement counts: You will track your baby's movements at least once a day by lying quietly on your side for a given amount of time and counting the number of movements you feel. Your doctor will tell you how many movements to expect within the given time frame -- fewer movements could indicate that your baby is not receiving enough oxygen and needs an assessment.

Amniocentesis: A small amount of amniotic fluid is withdrawn through a needle inserted into your abdomen. This may be done to check your baby's lung maturity.
In some cases, treatment may include reduced activity or bedrest and drinking extra fluids. You may need to take medication to stop labor if contractions begin early, as well as steroid medications to speed your baby's lung development if you're less than 34 weeks pregnant. Once your baby's lungs are mature, your doctor may recommend inducing labor or delivering the baby by C-section.

During labor, crystalloid liquid may be infused into the uterus to replace the greatly diminished amniotic fluid and prevent pressure on the umbilical cord. (The cord is normally protected from this pressure by the amniotic fluid.) Risks of this procedure, known as amnioinfusion, include overdistention of the uterus, prolapse of the umbilical cord through the vagina or uterine infection.

Early delivery by C-section may be needed if your baby is stressed.


Complications
Complications of oligohydramnios may include:
premature labor and birth
premature rupture of the membranes
uterine infection
underdevelopment of the baby's lungs
deformities (such as club foot or even amputation) due to adhesion of the amniotic sac to the baby
lack of oxygen to the baby (due to pressure on the umbilical cord, which normally floats in the amniotic fluid)
fetal distress
stillbirth
It's less common for oligohydramnios to develop early in pregnancy, but when it does, complications can be more severe.