Amnioinfusion is a procedure that adds fluid back into the uterus when amniotic fluid levels are too low. It’s most commonly performed during labor when a baby shows signs of a slow or irregular heart rate, typically caused by the umbilical cord getting compressed in a low-fluid environment. The procedure can also be used earlier in pregnancy as a diagnostic tool to get a clearer picture of fetal anatomy on ultrasound.
Why Amniotic Fluid Levels Matter
Amniotic fluid does more than cushion your baby. It acts as a buffer around the umbilical cord, which is the baby’s lifeline for oxygen and nutrients. When fluid levels drop too low, a condition called oligohydramnios, the cord can get squeezed between the baby and the uterine wall during contractions. Each compression temporarily reduces blood flow, causing intermittent drops in the baby’s heart rate that show up on the fetal monitor as “variable decelerations.”
If these heart rate dips become frequent or severe, they signal fetal distress and raise the likelihood of an emergency cesarean delivery. Amnioinfusion works by restoring a fluid cushion around the cord so it’s less likely to get pinched. The concept is straightforward: more fluid means more room, which means less pressure on the cord.
When Amnioinfusion Is Used
The most common reason is umbilical cord compression during labor. When monitoring shows repeated drops in the baby’s heart rate and fluid levels are low, adding fluid can stabilize those heart rate patterns and give labor a chance to continue safely.
It’s also used to dilute meconium, the baby’s first stool, which sometimes gets released into the amniotic fluid before or during delivery. If a baby inhales thick meconium while being born, it can cause a serious lung condition called meconium aspiration syndrome. A meta-analysis of 24 randomized studies involving nearly 6,000 participants found that amnioinfusion reduced the odds of meconium aspiration syndrome by 67%. The same analysis found significant improvements across nearly every newborn outcome measured, including fewer babies with low Apgar scores at five minutes, less neonatal acidosis, and fewer admissions to the neonatal intensive care unit.
In some cases, amnioinfusion is performed before labor begins, particularly when membranes rupture very early in pregnancy. Restoring fluid volume can help maintain the uterine environment and reduce the risk of preterm labor. Doctors may also use it as a diagnostic procedure during the second trimester. When amniotic fluid is extremely low, ultrasound images become difficult to interpret because there’s no contrast between the baby and surrounding tissue. Infusing fluid temporarily restores that contrast, allowing a much more detailed assessment of fetal anatomy. Research from the Journal of Clinical Medicine found that diagnostic amnioinfusion improved ultrasound visualization in the majority of cases and substantially improved diagnostic accuracy across all underlying causes of low fluid, whether structural abnormalities, growth restriction, or kidney dysfunction.
How the Procedure Works
There are two main approaches, and which one is used depends on when and why the procedure is being done.
During labor, the most common method is transcervical amnioinfusion. A thin, flexible catheter is placed through the cervix (which needs to be at least 1 to 2 centimeters dilated) and into the uterus. Sterile fluid, usually normal saline warmed to body temperature, is then slowly pumped through the catheter at a controlled rate. In research settings, infusion speeds of about 10 milliliters per minute under continuous ultrasound monitoring have been used, with fluid added until levels reach a target range.
When the procedure is done before labor, or when the membranes are still intact, a transabdominal approach is used instead. Guided by ultrasound, a small needle is inserted through the abdomen into the amniotic sac, similar to how an amniocentesis is performed. For pregnancies that need repeated infusions over a longer period, a small port can be placed under the skin to allow fluid delivery without repeated needle insertions.
What Happens During Monitoring
Throughout the infusion, the medical team continuously tracks two things: the baby’s heart rate and the pressure inside the uterus. The same catheter used to deliver fluid can also measure uterine pressure, which helps the team ensure that the added volume isn’t creating too much pressure in the uterine cavity. The baby’s heart rate is monitored on a fetal heart rate tracing, the same strip that’s been running throughout labor, to see whether the variable decelerations improve as fluid is added.
If the heart rate patterns stabilize and the baby tolerates the infusion well, labor can proceed. The fluid will gradually leak out over time, so the infusion may be adjusted or repeated as needed.
Risks and Limitations
Amnioinfusion is generally considered low-risk, but it’s not without potential complications. The primary concern is uterine hypertonus, a condition where resting pressure inside the uterus rises too high. One study that systematically measured uterine pressure during amnioinfusion found a significant increase in uterine tone both during and after the infusion, and documented at least one case where this led to a sustained drop in the baby’s heart rate. This is why close monitoring of uterine pressure is essential throughout the procedure.
Other uncommon risks include infection, since any time a catheter or needle enters the uterus there’s a small chance of introducing bacteria. Cord prolapse, where the umbilical cord slips ahead of the baby toward the cervix, is a rare but serious possibility. The added fluid volume could theoretically contribute to this in certain positions.
It’s also worth understanding that amnioinfusion doesn’t prevent all cesarean deliveries. A large U.S. population-based study of over 15 million deliveries found that cesarean rates for fetal distress were still high when amnioinfusion was used. However, among pregnancies with confirmed low fluid, the rate was lower with amnioinfusion (35.7%) than without it (38.5%), suggesting the procedure is most effective when low amniotic fluid is the underlying problem rather than other causes of fetal distress.
What It Feels Like
If you’re already in labor with an epidural, you likely won’t feel the catheter being placed or the fluid being infused. Without an epidural, you may feel mild pressure or a sensation of fullness as fluid enters the uterus. Some women notice fluid leaking from the vagina during or after the procedure, which is normal. The infusion itself doesn’t require you to stay still or change positions, and labor continues throughout the process. The goal is to make labor safer, not to delay it.