GUIDE
Oligohydramnios — low amniotic fluid — occurs when the amniotic fluid index (AFI) falls below 5 cm or the deepest single pocket of fluid measures less than 2 cm.
Amniotic fluid plays essential roles in fetal development, cushioning the baby, allowing movement, and supporting lung growth. Low fluid can develop for several reasons and the impact depends heavily on when in pregnancy it occurs and how low the levels are.
Be prepared from day one
Amniotic fluid is the warm, clear liquid that surrounds the baby inside the amniotic sac. In early pregnancy, it is produced primarily by the mother's body and the amniotic membrane. By the second trimester, the baby's kidneys take over as the main source — the baby swallows fluid, processes it through the kidneys, and urinates it back into the amniotic sac in a continuous cycle.
This fluid serves several critical functions: it cushions the baby from injury, allows freedom of movement for musculoskeletal development, supports lung growth (the baby "breathes" fluid in and out), maintains a stable temperature, and protects the umbilical cord from compression.
Fluid volume naturally increases throughout pregnancy, peaking at about 34 weeks (around 800 mL), then gradually decreasing. After 40 weeks, fluid levels can drop more significantly, which is one reason providers monitor post-term pregnancies closely.
The cause of low fluid significantly affects the prognosis and treatment approach. Your provider will evaluate for the underlying reason.
Low amniotic fluid is diagnosed on ultrasound. The two main measurement methods are the Amniotic Fluid Index (AFI) and the Single Deepest Pocket (SDP). AFI divides the uterus into four quadrants and adds the deepest pocket measurement in each — normal is 5 to 25 cm. SDP measures only the single deepest pocket — normal is 2 to 8 cm.
Oligohydramnios is diagnosed when AFI is below 5 cm or SDP is below 2 cm. Borderline low fluid (AFI 5 to 8 cm) may also warrant additional monitoring. Your provider may order additional tests to determine the cause, including detailed fetal anatomy scan (looking at kidneys and urinary tract), Doppler studies of placental blood flow, and testing for membrane rupture (fern test, AmniSure, or similar).
If you are managing low fluid alongside other complications, your pregnancy may be classified as high-risk.
The risks depend heavily on how low the fluid is, how early in pregnancy it developed, and the underlying cause. Mildly low fluid near term carries much less risk than severely low fluid in the second trimester.
Drink at least 8 to 12 glasses of water per day. Some studies have shown that maternal oral hydration (drinking 2 to 3 liters of water) can increase amniotic fluid levels, especially if dehydration contributed to the low levels. Some providers recommend IV fluid hydration in more significant cases. Hydration is a simple, low-risk intervention that may help.
Low amniotic fluid typically means more frequent monitoring — sometimes twice-weekly non-stress tests and weekly or biweekly ultrasounds to check fluid levels and fetal well-being. These appointments may feel burdensome, but they are critical for catching changes early. Missing appointments can delay important interventions.
If you experience a sudden gush of fluid or a constant trickle of clear fluid, go to labor and delivery immediately. Premature rupture of membranes (PPROM) is a common cause of low fluid and requires immediate evaluation. The fluid may be clear and odorless, making it easy to confuse with urine — when in doubt, get checked.
Lying on your left side optimizes blood flow to the placenta and kidneys, which can support fluid production. While bed rest alone does not cure oligohydramnios, left-side positioning during rest periods may provide a modest benefit and is recommended by many providers as a supportive measure.
Work with your provider to understand the delivery plan for your specific situation. If fluid is borderline low with normal testing, you may carry to term with close monitoring. If fluid is severely low, early delivery may be recommended. Understanding the plan — and the triggers that would change it — helps you feel more prepared.
Treatment depends on the cause, severity, and gestational age. If maternal dehydration is a contributing factor, increased oral fluid intake or IV hydration may help. If a specific medication is responsible, it will be discontinued. If premature rupture of membranes is the cause, management depends on gestational age — antibiotics to prevent infection and corticosteroids to mature the baby's lungs are standard.
Amnioinfusion — injecting saline directly into the amniotic cavity through a needle — is sometimes used during labor to reduce the risk of cord compression. It is a temporary measure used in specific clinical situations, not a long-term treatment.
For isolated oligohydramnios near term (low fluid without other concerning findings after 36 to 37 weeks), induction of labor is often recommended because the risks of continuing the pregnancy begin to outweigh the risks of delivery.
Changes in your symptoms or the baby's movement pattern should always be reported promptly when you have low fluid.
A gush of fluid or absent fetal movement requires immediate evaluation at labor and delivery.
The outlook for pregnancies with low amniotic fluid varies widely based on the cause, severity, and timing. Mild oligohydramnios near term — the most common scenario — generally has excellent outcomes with appropriate monitoring and timely delivery. Many babies born after pregnancies with borderline low fluid are perfectly healthy.
More severe or early-onset oligohydramnios requires careful management but can still have positive outcomes with expert care. Advances in neonatal medicine mean that even babies born early due to low fluid complications have improving survival and outcome rates.
For related information, see our guides on high-risk pregnancy, preeclampsia, gestational diabetes, placenta previa, and bleeding during pregnancy.
This guide is for informational purposes only and is not a substitute for professional medical advice. Always consult your healthcare provider with any questions about your pregnancy.
