Low amniotic fluid, called oligohydramnios, means the protective fluid surrounding your baby in the womb has dropped below a normal level. It affects roughly 11% of pregnancies, making it relatively common. Most cases are mild, develop in the third trimester, and lead to healthy deliveries with proper monitoring. But the timing, severity, and underlying cause all shape what it means for your pregnancy.
How Low Fluid Is Measured
Amniotic fluid levels are checked during a routine ultrasound using one of two methods. The amniotic fluid index (AFI) divides your uterus into four sections and adds up the deepest pocket of fluid in each. An AFI below 5 centimeters is considered low. The other method measures the single deepest pocket of fluid, called the maximum vertical pocket (MVP). An MVP below 2 centimeters also qualifies as oligohydramnios.
Your provider may check fluid levels at a routine anatomy scan or order a targeted ultrasound if your belly is measuring smaller than expected. Fluid levels naturally fluctuate throughout pregnancy, peaking around 36 weeks before gradually declining. A single low reading doesn’t always mean there’s a lasting problem, which is why repeat measurements are common.
What Causes It
In many third-trimester cases, no clear cause is found. When there is an identifiable reason, the most common include:
- Placental problems. If the placenta isn’t delivering enough blood and nutrients, the baby produces less urine, which is the primary source of amniotic fluid in the second half of pregnancy.
- Ruptured membranes. A slow leak in the amniotic sac (sometimes called premature rupture of membranes, or PROM) can drain fluid gradually. You might notice a steady trickle of clear fluid, though small leaks are easy to miss.
- Going past your due date. Fluid levels naturally drop after 40 weeks. Pregnancies that extend more than two weeks past the due date carry a higher risk of low fluid.
- Fetal kidney or urinary tract issues. Because the baby’s urine replenishes amniotic fluid, conditions that affect kidney development or block the urinary tract can reduce fluid production.
- High blood pressure or preeclampsia. These conditions affect blood flow to the placenta, which in turn can lower fluid levels.
- Maternal dehydration. Being significantly dehydrated reduces your blood volume, which can temporarily lower amniotic fluid.
Why Amniotic Fluid Matters for Your Baby
Amniotic fluid does more than cushion your baby. It plays a direct role in organ development, especially the lungs. During the second trimester, roughly weeks 16 through 24, lung tissue grows rapidly. The fluid filling the baby’s airspaces creates internal pressure and stretch that drives lung growth. Low fluid during this critical window can shrink the space inside the baby’s chest, disrupting that growth and potentially leading to underdeveloped lungs at birth.
Fluid also gives the baby room to move. Those kicks and stretches aren’t just reassuring for you; they help muscles, joints, and limbs develop normally. Severely low fluid over a prolonged period can restrict movement enough to affect limb positioning. The fluid additionally acts as a barrier against infection and helps maintain a stable temperature around the baby.
Risks Depend on Timing
Low fluid discovered in the second trimester is more concerning than a third-trimester finding. Earlier in pregnancy, the baby’s lungs and other organs are still forming, and prolonged low fluid during that period raises the risk of breathing difficulties after delivery. The earlier and more severe the drop, the greater the potential impact on lung development.
In the third trimester, the primary concern shifts to the umbilical cord. With less fluid to float in, the cord is more likely to get compressed between the baby and the uterine wall, especially during contractions. A compressed cord reduces the flow of oxygen and nutrients to the baby. This is why third-trimester oligohydramnios leads to closer fetal monitoring during labor, and sometimes a recommendation for earlier delivery.
Signs You Might Notice
Most people with low amniotic fluid don’t feel any obvious symptoms. The condition is typically caught on ultrasound rather than through physical signs. That said, some things can prompt your provider to check fluid levels: measuring smaller than expected for your gestational age, a noticeable decrease in your baby’s movements, or leaking fluid from the vagina (which could signal a membrane rupture). If you experience a sudden gush or steady trickle of clear, odorless fluid, contact your provider right away.
How It’s Managed
Treatment depends on how far along you are, how low the fluid is, and what’s causing it. In mild cases near the end of pregnancy, increased monitoring may be all that’s needed. Your provider will likely schedule more frequent ultrasounds and non-stress tests to track the baby’s heart rate and movement patterns.
Staying well-hydrated is one of the simplest interventions. Studies show that drinking about 2 liters of water can increase amniotic fluid levels by around 30%. In pregnancies without other complications, oral hydration alone has been associated with a 20 to 30% improvement in fluid index and a lower rate of cesarean delivery. It’s not a guaranteed fix, but it’s often the first step.
Rest can also help, particularly if high blood pressure is contributing to the problem. Lying down improves blood flow to the placenta, which can support fluid production and buy time before delivery.
In some situations, your medical team may use a procedure called amnioinfusion, where sterile saline is introduced into the uterus. During labor, this can reduce cord compression and lower the risk of fetal distress. Earlier in pregnancy, it’s sometimes used to temporarily restore fluid volume so the baby can be seen more clearly on ultrasound for further evaluation.
If fluid levels remain critically low and the baby shows signs of distress, or if other tests suggest the baby isn’t tolerating the environment well, your provider may recommend delivering early. For pregnancies past the due date with confirmed low fluid, induction or cesarean delivery is standard. The goal is always balancing the risks of prematurity against the risks of leaving the baby in a low-fluid environment.
What Most Pregnancies Look Like
A diagnosis of low amniotic fluid can feel alarming, but the majority of cases, particularly those found in the late third trimester, result in healthy outcomes with closer monitoring. Your care team will want to understand why the fluid is low and will adjust your visit schedule accordingly. Many people with mild oligohydramnios go on to deliver vaginally at or near their due date. The key variable is the underlying cause: isolated low fluid with an otherwise healthy baby and placenta carries a much better outlook than low fluid combined with growth restriction or a fetal anomaly.