About Amniotic Fluid

Amniotic fluid is the fluid that surrounds the baby inside the amniotic sac during pregnancy. It plays many important roles in fetal growth and development.

Amniotic fluid helps:

• support lung development

• support movement and musculoskeletal development

• protect the baby from pressure and injury

• help prevent compression of the umbilical cord

• maintain space for fetal growth and movement

The amount and source of amniotic fluid change throughout pregnancy. As pregnancy progresses, fetal urine becomes a major source of amniotic fluid, along with fluid produced by the fetal lungs and other pathways.

After PPROM, amniotic fluid may leak through an opening in the membranes. The amount of fluid remaining can vary considerably from one one ultrasound to another.

Amniotic Fluid After PPROM

The body may continue to produce amniotic fluid after the membranes rupture. At the same time, fluid may continue to leak.

Because both processes can occur at once, amniotic fluid levels after PPROM may:

• remain low

• fluctuate from one measurement to another

• temporarily increase

• remain measurable despite continued leaking

The amount of fluid seen on ultrasound does not necessarily correspond with how much leaking a patient notices. Some people with confirmed PPROM continue to have measurable or even relatively normal fluid levels.

Measuring Amniotic Fluid

Amniotic fluid is measured using ultrasound. Two methods are commonly used:

Amniotic Fluid Index — AFI

For the Amniotic Fluid Index, the uterus is divided into four sections, or quadrants.

The deepest vertical pocket of fluid in each quadrant is measured.

The four measurements are added together to calculate the AFI.

An AFI of 5 cm or less is commonly used to describe oligohydramnios.

Single Deepest Pocket — SDP

With the Single Deepest Pocket method, the largest visible vertical pocket of amniotic fluid is measured.

A deepest vertical pocket of less than 2 cm is commonly used to describe oligohydramnios. This is sometimes called the maximum vertical pocket or deepest vertical pocket.

Different healthcare providers and hospitals may use different methods depending on the pregnancy and clinical circumstances.

Oligohydramnios and Anhydramnios

Oligohydramnios means there is less amniotic fluid than expected.

Anhydramnios generally refers to very little or no measurable amniotic fluid on ultrasound.

These terms describe what is visible at the time of the ultrasound. They do not mean that the body has completely stopped producing fluid. After PPROM, fluid measurements can change over time.

Amniotic Fluid and Lung Development

Amniotic fluid is particularly important for fetal lung development.

When PPROM occurs very early in pregnancy, prolonged periods of very low amniotic fluid may interfere with normal lung development and increase the risk of pulmonary hypoplasia.

Pulmonary hypoplasia means that the lungs have not developed to their expected size or capacity.

Risk varies considerably between pregnancies and may be affected by:

• gestational age when PPROM occurs

• gestational age at delivery

• length of time with very low fluid

• amount of residual amniotic fluid

• fetal growth and development

• other pregnancy complications

An individual fluid measurement cannot predict whether pulmonary hypoplasia will occur or how severe respiratory problems may be after birth.

Learn more about Pulmonary Hypoplasia

Amniotic Fluid and Infection

Amniotic fluid contains substances involved in the body's natural defenses against microorganisms.

However, one of the important functions of the intact amniotic membranes is maintaining a barrier between the pregnancy and microorganisms in the lower reproductive tract.

When the membranes rupture, that barrier is disrupted and the risk of ascending infection becomes an important concern.

Amniotic fluid levels alone cannot determine whether infection is present.

Patients with PPROM should follow their healthcare team's instructions for monitoring symptoms and seeking medical evaluation.

Exams and Ultrasound After PPROM

Amniotic fluid measurements are performed using ultrasound.

PPROM evaluation may also include a sterile speculum examination to look for leaking or pooling of amniotic fluid.

Healthcare providers generally try to avoid unnecessary digital cervical examinations after PPROM because repeated digital examinations may increase infection risk and may shorten latency.

There may be circumstances in which an internal examination is medically necessary. Your healthcare team can explain why a particular examination is being recommended.

Can Drinking More Water Increase Amniotic Fluid?

Hydration is important during pregnancy.

Studies in pregnancies with low amniotic fluid have found that increasing maternal hydration can sometimes increase the amount of fluid measured on ultrasound.

However, this is not the same as repairing ruptured membranes or stopping an amniotic fluid leak.

Research has not established that drinking extra fluids after PPROM:

• seals ruptured membranes

• prevents infection

• prevents pulmonary hypoplasia

• or reliably prolongs latency

Parents should follow their healthcare team's recommendations about hydration, particularly if another medical condition affects how much fluid they should drink.

Every Fluid Measurement Is One Part of the Picture

After PPROM, it is natural to focus closely on the number reported after each ultrasound. An AFI or deepest-pocket measurement is only one piece of information.

Healthcare teams may also consider:

• gestational age

• fetal growth

• fetal wellbeing

• infection or inflammation

• bleeding or placental complications

• labor

• length of latency

• and the overall health of the patient and baby

One fluid measurement cannot predict the outcome of an individual PPROM pregnancy.

If you have questions about your fluid measurements, ask your healthcare team what the number means in the context of your pregnancy.

Research & Additional Reading

Current Clinical Information

American College of Obstetricians and Gynecologists — Indiciations for Outpatient Antenatal Fetal Surveillance

Includes current definitions and clinical use of single deepest vertical pocket measurements for oligohydramnios.

Read ACOG Guidance

Amniotic Fluid Physiology

Amniotic Fluid: Physiology and Assessment

Overview of amniotic fluid production, regulation, function and assessment.

Read the Article

Maternal Hydration

Maternal Hydration for Increasing Amniotic Fluid Volume in Oligohydramnios and Normal Amniotic Fluid Volume

Systematic review examining whether maternal hydration changes measured amniotic fluid volume.

Read the Cochrane Review

PPROM, Amniotic Fluid & Respiratory Outcomes

PROMISE — Impact of Maternal and Neonatal Risk Factors on the Respiratory Outcome of Extremely Preterm Infants Following PPROM in the Second Trimester of Pregnancy

Recent research examining respiratory outcomes following second-trimester PPROM, including the relationship between prolonged low amniotic fluid and respiratory outcomes.

Read the Study

Information reviewed: August 2026