Seeing 'low amniotic fluid' in a report can be worrying. In reality, it is simply a measurement, and the impact on your baby depends on several factors that your doctor will evaluate together. This guide explains 'oligohydramnios' (low amniotic fluid) in simple terms so that you feel less confused at your next appointment.
What is amniotic fluid, and why does your baby need it?
Amniotic fluid is a clear, pale yellow liquid that surrounds the baby. It supports the baby,
allows room for movement, aids in lung development, and protects the fetus. From the second
trimester onwards, the majority of this fluid is produced from the baby's own urine; therefore,
the fluid level indicates how well the baby's kidneys are functioning and reflects the overall
status of the pregnancy.
Oligohydramnios during pregnancy means that the amount of amniotic fluid is below the level
considered normal by doctors. Medical reports may state "low amniotic fluid" or "low amniotic
fluid level"; both terms mean the same thing.
What does "low amniotic fluid" mean?
Low amniotic fluid means there is less fluid around your baby than expected for your stage of pregnancy. Doctors call this 'oligohydramnios' (pronounced: OL-ih-goh-HY-dram-nee-os). Your report might also state "reduced liquor" or "decreased AFI"; these all mean the same thing. It is a condition detected during a scan, not a disease in itself.
Is low amniotic fluid dangerous for the baby?
The honest answer is: it depends on several factors. If the baby is growing well but the reading is slightly low during the later stages of pregnancy, doctors often order a repeat scan. Doctors frequently detect 'oligohydramnios' (low amniotic fluid) in the third trimester; for instance, during a routine growth scan at 36 weeks. If fluid levels are very low or are low early in the pregnancy, closer monitoring is required, as the fluid aids lung development and provides space for the baby to grow. A low reading indicates that the doctor needs to examine the situation more closely; it does not lead to a definitive conclusion about the baby's condition.
How does the scan measure the fluid?
No blood test is necessary. The sonographer measures the fluid on ultrasound, painlessly, in a few minutes, using one of two methods:
- Amniotic fluid index (AFI): the sonographer divides the womb into four parts, measures the deepest pocket of fluid in each, and adds the four numbers.
- Single deepest pocket (SDP): the sonographer measures only the largest clear pocket of fluid.
The sonographer measures the amount of fluid in centimeters. If the AFI is approximately 5 cm or
less, it is considered low; similarly, if the deepest pocket measures less than 2 cm, that is
also considered low. The normal range for AFI extends from slightly above 5 cm to approximately
25 cm; therefore, if the measurement falls within this range, it indicates that the fluid level
is within normal limits.
A single number doesn't tell the whole story. Different centers use slightly different cut-off
values, and normal levels also change as the pregnancy progresses. Therefore, doctors interpret
that number in the context of how many weeks pregnant the mother is and what else is visible on
the scan. When an ultrasound report indicates low fluid, it simply means the measurement has
fallen below the normal range.
Why does it happen?
There can be several reasons for low amniotic fluid, and often doctors are unable to identify a specific cause. Common causes include:
- Leaking of fluid through a small tear in the amniotic sac (water sac)
- The baby receiving insufficient nutrition from the placenta, which can slow down growth
- Pregnancy continuing beyond the due date, when fluid levels naturally decrease
- Issues with the baby's urinary tract (this is rare)
- Maternal conditions, such as high blood pressure or the use of certain medications
In most cases, this did not happen because of anything the mother did.
Will the mother feel anything?
Low amniotic fluid symptoms usually do not appear. Most mothers feel completely normal and learn about it only from a routine scan. Some mothers may notice reduced fetal movement, an abdominal size smaller than expected, or fluid leakage. If a mother experiences any of these symptoms, she should seek a medical check-up immediately.
What usually happens after the scan?
Doctors do not focus solely on the fluid levels; they also assess the baby's growth and estimated weight, blood flow via a color Doppler scan, and the condition of the baby's kidneys and bladder. A follow-up scan after a few days reveals whether the fluid level remains stable, increases, or decreases. Based on these findings, doctors then determine the course of further testing and the timing of the delivery.
When should the mother call the doctor the same day?
- Leaking of fluid or a sudden gush of water
- Reduced fetal movement compared to normal
- Fever, abdominal pain, or bleeding
The mother should not wait for the next appointment if she notices any of these.
Quick answers
Can a low reading be a mistake?
Measurements vary with the baby's position and the way the sonographer does the scan, so doctors often repeat the scan before they draw conclusions.
Can the number change between scans?
Yes. It can rise, stay the same or fall, which is why one reading rarely tells the whole story.
Can it improve?
Sometimes it does, particularly with borderline readings. The doctor can say whether that is likely in each case.
Not sure what the report means? Our fetal medicine team at Excellence Imaging & Fetal Medicine in Janakpuri can go through the scan and reports with the mother and her family.