Low amniotic fluid often has no obvious symptoms you can detect on your own. Most cases are found during routine prenatal ultrasounds, where your provider measures fluid levels using standardized criteria. Still, there are a few physical signs that can raise suspicion, and understanding what gets measured and why can help you know what questions to ask at your next appointment.
Signs You Might Notice
Three things may tip you or your provider off to low fluid levels. First, your uterus may measure smaller than expected for your stage of pregnancy. During prenatal visits, your provider measures from your pubic bone to the top of your uterus. If that number consistently falls short of the expected range, low fluid is one possible explanation.
Second, you may notice your baby moving less than usual. Amniotic fluid gives the baby room to move, and when there’s less of it, movements can feel weaker or less frequent. If you’re used to regular kicks and they suddenly slow down, that’s worth reporting.
Third, you might notice fluid leaking from your vagina. This is the most actionable sign because it can indicate your membranes have ruptured, which is one of the most common causes of low fluid. The tricky part is figuring out whether the fluid is actually amniotic fluid, urine, or normal vaginal discharge.
Amniotic Fluid vs. Urine vs. Discharge
Amniotic fluid is typically clear or slightly white, sometimes tinged with mucus or a small amount of blood. It has no smell. When it leaks, it tends to soak through your underwear and may come in a gush or a slow, steady trickle you can’t control by squeezing your pelvic floor muscles (unlike urine). It often continues leaking when you change position or stand up.
Normal vaginal discharge is usually sticky and comes in small amounts. It can be clear, cloudy, milky white, yellow, or green, and sometimes has a mild fishy odor. Urine, obviously, has its own distinct smell and typically comes when you sneeze, cough, or laugh, which is common in late pregnancy.
If you’re soaking through a pad with odorless, watery fluid and you’re not sure what it is, contact your provider. They can run a quick test to confirm whether it’s amniotic fluid.
How Providers Test for a Leak
When you come in with suspected fluid leaking, your provider will typically do a speculum exam and look for visible pooling of fluid. From there, they may use one of several tests. Nitrazine paper changes color when exposed to amniotic fluid because it’s more alkaline than urine or discharge. This test is highly sensitive (90 to 97%) but can give false positives from blood, semen, infections, or soap. A ferning test looks at dried fluid under a microscope for a fern-like crystallization pattern unique to amniotic fluid.
Newer biochemical tests like Amnisure detect specific proteins found only in amniotic fluid and are more reliable, with sensitivity rates of 96 to 99% and very high accuracy overall. If the leak is confirmed, an ultrasound follows to check how much fluid remains.
How Low Fluid Is Measured on Ultrasound
Low amniotic fluid, clinically called oligohydramnios, is diagnosed using one of two ultrasound measurements. The amniotic fluid index (AFI) divides your uterus into four quadrants and adds up the deepest pocket of fluid in each one. An AFI of 5 cm or below indicates low fluid. The single deepest pocket (SDP) method measures just the single largest pocket of fluid. An SDP below 2 cm is the threshold.
Your provider may also make a subjective assessment during the ultrasound, simply noting that the fluid looks visually reduced. But the numerical measurements are preferred because they give a concrete baseline and make it easier to track changes over time.
What Causes Low Fluid
The most straightforward cause is ruptured membranes, where your water breaks or develops a small tear and fluid slowly leaks out. But several other factors can reduce fluid levels without any visible leaking:
- Placental problems: If the placenta separates from the uterine wall early or isn’t delivering enough blood flow to the baby, fluid production drops.
- Maternal health conditions: Chronic high blood pressure and diabetes both increase the risk.
- Medications: Certain blood pressure medications (ACE inhibitors) can reduce amniotic fluid.
- Fetal conditions: Problems with the baby’s kidneys or urinary tract can lower fluid, since the baby’s urine is a major source of amniotic fluid in the second and third trimesters. Restricted fetal growth and some genetic disorders also play a role.
In many cases, especially near the end of pregnancy, fluid naturally decreases and no specific cause is identified. Amniotic fluid peaks around 36 weeks and declines after that, so mild low readings close to your due date are relatively common.
Why Timing Matters
Low fluid carries different risks depending on when it happens. In the second trimester, the baby’s lungs are still developing, and adequate fluid is essential for that process. The baby essentially “breathes” the fluid, which helps the lungs expand and mature. Significantly low fluid during this window can lead to underdeveloped lungs and limb compression.
In the third trimester, the primary concerns shift to umbilical cord compression. With less fluid cushioning the cord, contractions or the baby’s movements can temporarily pinch it, reducing oxygen flow. This is why providers monitor babies more closely once low fluid is identified, often with nonstress tests or biophysical profiles to check the baby’s heart rate patterns and movement.
What Happens After a Diagnosis
Management depends on how low the fluid is, what’s causing it, and how far along you are. If you’re near your due date, your provider may recommend inducing labor rather than waiting, since the risks of low fluid can outweigh the benefits of staying pregnant longer.
Earlier in pregnancy, the approach is more conservative. You’ll likely have more frequent ultrasounds to track fluid levels and fetal well-being. Your provider may recommend increased hydration. A Cochrane review of four trials found that women who drank about two liters of water over two hours saw a meaningful increase in amniotic fluid volume on follow-up ultrasound. This isn’t a cure, but it can provide a temporary boost and is a low-risk intervention worth trying.
If the cause is a medication you’re taking, your provider may switch you to an alternative. If ruptured membranes are the issue before the baby is viable, the decision-making becomes more complex and involves weighing infection risk against the benefits of prolonging pregnancy.
In isolated cases where fluid is borderline low and no other complications exist, many pregnancies continue normally with close monitoring. The key is regular follow-up so your care team can catch any downward trend early and adjust the plan accordingly.