Oligohydramnios is an abnormal condition occurring during pregnancy resulting from lack of amniotic fluid (fluid surrounding the baby in the uterus) . This fluid plays a vital role in proper fetal development while its deficiency can lead to oligohydramnios sequence or Potter sequence characterized by an irregular appearance of the fetus or neonate. The onset of oligohydramnios usually occurs during the later part of the third trimester, often when one is overdue.
The opposite to oligohydramnios is polyhydramnios, characterized by excessive amniotic fluid levels.
In many cases, oligohydramnios is idiopathic with experts still trying to find out the exact cause responsible for the problems. The fetal urine mainly forms the amniotic fluid during the later stages of pregnancy. So, reduction in fetal urine production due to some pregnancy irregularity, such as obstruction of the fetal urinary tract, can lead to oligohydramnios. Signs of low amniotic fluid levels during the first or second trimester may indicate some fetal abnormalities.  The common contributing factors include:
Leaky or Ruptured Amniotic Membranes: Sometimes, the amniotic fluid leaks out through a small tear or hole in the amniotic membranes, leading to Oligohydramnios. This can occur at any stage of pregnancy but is most common as one approaches delivery. 
Fetal Abnormalities: Absence of the kidney or any other kidney abnormality (renal agenesis, polycystic kidney) in the baby can also hamper urine production
Genetic Factors: Inheriting abnormal genes in an autosomal recessive or autosomal dominant pattern
Placental Abruption : Placental abnormalities, like a partial abruption, which causes the placenta to peel away from the inner uterus wall, may lead to amniotic fluid deficiency. Any irregularity in the placental blood and nutrient supply can prevent the baby from producing urine which may lead to serious complications.
Carrying Twins: Women pregnant with twins or multiples are at a higher risk of low amniotic fluid levels. Twin-to-twin transfusion syndrome (a condition where one twin experiences severe amniotic fluid deficiency while the other has excessive amounts of fluid) can also cause oligohydramnios.
Using NSAIDs like indometacin and certain ACE (angiotensin-converting enzyme) inhibitors 
The following medical conditions in the mother are considered to increase the risk of oligohydramnios :
It may or may not cause any detectable signs in the affected women . In case of a ruptured amniotic sac, one may notice a constant feeling of wetness due to vaginal fluid leakage. The belly may also look smaller than it should at a certain gestational age.
Oligohydramnios occurring during the first and the second trimester is more likely to cause serious complications than when it occurs during the third trimester .
Oligohydramnios can lead to the following problems when occurring during the third trimester:
The doctor may order a number of diagnostic tests to detect any fetal abnormalities while the mother may be asked various questions regarding any chronic health problems.
Ultrasound helps to confirm the diagnosis while also helping to make the differential diagnosis. It is often used for observing the fetal kidney and bladder to rule out the possibility of cystic dysplasia, renal agenesis and ureteral obstruction.
The test is also useful for checking the fetal growth to eliminate the possibility of IUGR (intrauterine growth restriction) responsible for oliguria. A specific form of ultrasound named the Doppler ultrasound  is used for assessing placental insufficiency, in case it is suspected. The diagnostic criteria include:
Amniotic Fluid Index (AFI) : There are a number of tests available for measuring the amniotic fluid volume (AFV), with AFI being the most commonly used procedure. Around 8% of all pregnant women may have low amniotic fluid levels with 4% among them diagnosed with oligohydramnios.
Maximum Vertical Pocket (MPV): This test allows doctors to check the amniotic fluid levels in the deepest part of the uterus.
It helps to detect any rupture of membranes (ROM) responsible for oligohydramnios.
Blood tests, like maternal serum screening, can be performed to detect low levels of amniotic fluid in the uterus as well as to determine the chances of the baby being born with congenital disorders like Down syndrome and spina bifida.
Prevention is not possible in the idiopathic cases. However, taking certain measures may reduce its risks :
Women who have a healthy pregnancy, developing mild oligohydramnios towards the later stages often do not need any treatment. In such cases, the doctor monitors the fetal heart rate, lung development as well as the baby’s movements closely using ultrasound and other similar tests. Delivery is the most appropriate management option if oligohydramnios occurs during the last stage of pregnancy. More severe cases of pre-term oligohydramnios may require the following treatment measures:
It involves infusing sodium chloride solution (room-temperature) into the amniotic cavity using an intrauterine catheter to maintain normal amniotic fluid levels. 
This treatment procedure involves diverting the fetal urine into the uterus in women with fetal obstructive uropathy that causes oligohydramnios. Vesico-amniotic shunts are quite effective in managing the low amniotic fluid levels; however, their efficacy in maintaining proper renal and pulmonary functions is still doubtful.
Injecting fluids through amniocentesis prior to delivery. Although, the condition tends to return within a few weeks after administering the injection, it allows doctors to understand the fetal anatomy properly enabling them to better manage the problem in the future.
Using oral fluids and IV fluids to rehydrate the mother’s body helps to raise the amniotic fluid levels. Due to this reason, doctors often ask affected mothers to drink plenty of water.
Prescribing complete bed rest to the mother, along with proper hydration, helps to promote the amniotic fluid production by increasing her intravascular space. 
Termination of pregnancy may be the only option in severe cases occurring during the first trimester.
The prognosis depends on the stage of pregnancy during which the condition first occurs . The earlier it occurs the poorer the chances of survival for the infant. Fetal mortality rate ranges between 80% and 90% in cases where oligohydramnios is first diagnosed during the second trimester. The chances of recurrence in any future pregnancies depend on the exact causes of the condition.
Its ICD-9 code is 658.0 while the ICD-10 code is O41.0.
March of Dimes National Office
1275 Mamaroneck Avenue
White Plains, New York State 10605
Phone: (914) 997-4488