What is Oligohydramnios?
Oligohydramnios is a condition seen during pregnancy where there is a less than normal amount of amniotic fluid within the amniotic sac. The amniotic fluid functions as a cushion that protects the fetus inside the womb and also helps in the transfer of nutrients and fluids between it and the mother.
Is Oligohydramnios a Medical emergency?
Oligohydramnios is not a medical emergency, but early identification and management are essential to avoid complications.
Oligohydramnios may be caused by the following:
- Premature rupture of membranes
- Fetal urinary tract abnormalities - Amniotic fluid is mostly comprised of fetal urine in the second half of the pregnancy, therefore a fetal urinary tract abnormality such as the following can cause Oligohydramnios.
- Renal agenesis
- Polycystic kidney
- Obstructive lesions of the fetal urinary tract
- Placental insufficiency - A condition where the placenta is unable to supply sufficient nutrient and oxygen, it can be caused by:
- Pregnancy - Induced hypertension
- Maternal diabetes
- Post maturity syndrome - When the pregnancy extends beyond 42 weeks
- Maternal use of certain medications such as - Prostaglandin synthase inhibitors, or angiotensin-converting enzyme inhibitors, COX inhibitors.
- Intrauterine infections during pregnancy
- Fetal chromosomal anomalies
Some risk factors for Oligohydramnios may include:
- Maternal substance abuse
- Autoimmune diseases in the mother
- Liver disease in the mother
- Maternal diabetes
- Maternal hypertension
Signs & symptoms
The symptoms and signs of Oligohydramnios may include:
- Abnormal fundal height - The distance between the top of the uterus and the pubic bone is less than what is normal according to the period of pregnancy.
- The position of the fetus inside the uterus is not normal - It may be presented with the bottom or shoulders first.
- The fetal parts such as the head or limbs may be unduly prominent and felt through the mother’s abdomen.
The following investigations may be done for Oligohydramnios:
- Laboratory tests:
- CBP & ESR
- Complete urine examination
- Renal function tests
- Liver function tests
- Lecithin sphingomyelin ratio (L:S) - To assess fetal lung condition
- Phosphatidylglycerol concentration - To assess fetal lung condition
- Autoantibody tests - To rule out systemic lupus erythematosus(SLE)
- Tox screen - To check for maternal substance abuse
- Imaging tests:
- Serial amniotic fluid index (AFI) measurement
- Uterine artery doppler study - To assess placental insufficiency
- Transabdominal instillation of indigo carmine - To assess premature rupture of membranes
A diagnosis of Oligohydramnios is established based on medical history, clinical evaluation, and results of the investigations done. A diagnosis of Oligohydramnios has suspected if the amniotic fluid is less than 8 cm on ultrasound, and is confirmed if it is less than 5 cm.
Other diagnostic indicators are as follows:
- Uterine size is much smaller than usual for the period of pregnancy
- There are fewer fetal movements
- The uterus is filled with the fetus because of the absence of amniotic fluid
- There is fetal malpresentation inside the uterus
- There is evidence of intrauterine growth retardation (IUGR) of the fetus
- Fetal tract abnormality is suspected when there is an absence of normal filling and emptying of the fetal bladder
The aim of the treatment of Oligohydramnios depends on the time of diagnosis and the severity of the condition, and also on the presence or absence of any fetal abnormalities.
Medical management of Oligohydramnios may include the following:
- Rehydration - Either oral or intravenous rehydration of the mother is done to increase the volume of the amniotic fluid. Oral or iv rehydration of up to 2 liters/day may be done.
Interventional including surgery and indications for surgery
The following may be done:
- Amnioinfusion - It is done by introducing an isotonic sodium chloride solution through the cervix. (It is done at centers specializing in invasive fetal medicine).
- It is usually done during the second trimester via the abdominal route
- It may be done at the time of delivery to reduce umbilical cord compression, fetal distress, and aspiration of the meconium
- Induced or cesarian delivery - is indicated in cases of postmaturity
Role of diet/ Exercise/ Lifestyle changes/ Preventive measures
The following measure may be effective in the management of Oligohydramnios:
- Complete rest - It is believed to help not only in increasing the amniotic fluid levels but may also help if there is pregnancy-induced hypertension.
- Genetic Counseling may be required if fetal abnormalities are suspected or detected
The following complications may occur in the presence of Oligohydramnios:
- Marked deformation of the fetus - Which may include,
- Flattened face, low set ears, mongoloid slant, micrognathia (undersized jaws)
- Thoracic (chest) compression and narrow chest
- Bowed legs and clubbed feet
- Lung defects - Small-sized fetal lungs
- Gastrointestinal tract defects
- Intra-uterine growth retardation of the fetus
- Cord compression
The prognosis of Oligohydramnios is generally good if identified early and managed well.
When to contact the doctor or hospital? / How to identify the emergency or complications?
It is advisable to seek medical attention if any of the symptoms of Oligohydramnios are noticed especially if the enlargement of the abdomen is not by the duration of the pregnancy, and the fetal movements are reduced.
Indications for hospitalization if required
Hospitalization is required for the management of Oligohydramnios, especially if it is observed or diagnosed after 26 weeks of pregnancy.
Serial amniotic fluid index measurement is required till the time of delivery if Oligohydramnios has been diagnosed.
Suggested clinical specialist/ Departments to consult for this condition
Oligohydramnios will be attended by specialists from the Department of Maternal-fetal Medicine, Gynecology & Obstetrics, Additional Consultations with a Pediatric Nephrologist and Pediatric Surgeon may be required.