Amniotic Fluid During Pregnancy: What It Is, Normal Levels, How It’s Measured & Why It Matters

If you have ever watched your baby moving around during an ultrasound, you may have noticed the dark space surrounding your baby on the screen.

That is amniotic fluid, and it plays an incredibly important role throughout pregnancy.

Parents often ask us:

"Is there enough fluid around my baby?”“What is a normal amniotic fluid level?”

“Can drinking more water increase amniotic fluid?"

Let’s break it down in a simple way.

What Is Amniotic Fluid?

Amniotic fluid is the liquid that surrounds your baby inside the

amniotic sac.

Early in pregnancy, the fluid comes largely from maternal sources. As pregnancy progresses, fetal urine becomes a major contributor to amniotic fluid, while your baby also swallows fluid as part of the normal circulation of amniotic fluid.

It may sound surprising, but this is a normal and important part of fetal development.

Think of amniotic fluid as your baby's own protected environment during pregnancy.

Why Is Amniotic Fluid So Important?

Amniotic fluid does much more than simply surround your baby.

It helps:

• Cushion and protect your baby

• Allow your baby to move freely

• Support normal development of the lungs

• Provide room for muscles, bones, and limbs to develop

• Help prevent compression of the umbilical cord

• Maintain a relatively stable environment around your baby

This is why healthcare providers pay attention to amniotic fluid during pregnancy, especially later in pregnancy.

How Do We Measure Amniotic Fluid on Ultrasound?

We cannot simply look at an ultrasound and know exactly how many ounces of fluid are present.

Instead, clinicians estimate the amount using ultrasound.

Two commonly used methods are the Amniotic Fluid Index (AFI) and the Single Deepest Pocket (SDP), sometimes called the maximum vertical pocket.

1. Amniotic Fluid Index, or AFI

For AFI, the uterus is divided into four quadrants.

The deepest vertical pocket of fluid in each quadrant is measured in centimeters, and those four measurements are added together.

For a singleton pregnancy, commonly used ultrasound thresholds are:

AFI greater than 5 cm and less than 24 cm: generally considered normal

AFI 5 cm or less: consistent with oligohydramnios, or low amniotic fluid

AFI 24 cm or greater: consistent with polyhydramnios, or increased amniotic fluid

These are clinical thresholds, and the meaning of a measurement depends on gestational age and the overall pregnancy picture. Merck Manuals

2. Single Deepest Pocket

Another method measures the single deepest vertical pocket of fluid that does not contain fetal parts or the umbilical cord.

Commonly used ranges are:

2 cm to less than 8 cm: normal

Less than 2 cm: low

8 cm or greater: high

SMFM defines polyhydramnios in a singleton pregnancy as a deepest vertical pocket of at least 8 cm or an AFI of at least 24 cm. SMFM Publications

What Does Low Amniotic Fluid Mean?

A lower-than-expected amount of amniotic fluid is called oligohydramnios.

There are several possible reasons for low fluid. These can include leaking or ruptured membranes, placental problems, certain fetal conditions, some medications, or other pregnancy complications. Sometimes the cause is not immediately obvious. Merck Manuals

This is important because low amniotic fluid is not something that should be diagnosed or managed through an elective ultrasound alone.

If low fluid is suspected, your OB, midwife, or maternal-fetal medicine specialist should evaluate the pregnancy and determine whether additional monitoring or testing is needed.

What Does Too Much Amniotic Fluid Mean?

An increased amount of amniotic fluid is called polyhydramnios.

Mild cases sometimes have no identifiable cause. Other cases can be associated with conditions such as maternal diabetes, multiple pregnancy, fetal abnormalities, anemia, infections, or other conditions affecting the pregnancy. Merck Manuals

Again, finding increased fluid does not by itself tell us why it is happening.

That is why abnormal fluid measurements need to be evaluated by a diagnostic pregnancy provider.

Can Drinking More Water Increase Amniotic Fluid?

This is probably one of the questions I hear most:

"If my fluid is low, should I just drink more water?”

Hydration is important during pregnancy, and research has found that increasing maternal hydration can increase measured amniotic fluid volume in some circumstances. However, hydration is not a treatment for every cause of low amniotic fluid, and the available research has not established that simply drinking more water resolves the underlying problem or improves all important pregnancy outcomes. Cochrane Library

So if your doctor tells you that your fluid is low, follow their specific recommendations rather than trying to treat the number yourself.

Low fluid caused by dehydration is very different from low fluid related to ruptured membranes, placental function, fetal urinary tract problems, or another medical condition.

The cause matters.

What Can You Do to Support Healthy Amniotic Fluid?

For most uncomplicated pregnancies, the best approach is simple:

Stay adequately hydrated, attend your prenatal appointments, pay attention to your baby's movements when you've reached the stage where your provider has advised movement monitoring, and complete any recommended diagnostic ultrasounds.

There is no special food, juice, supplement, or home remedy that can guarantee a normal amniotic fluid level.

If a measurement is abnormal, your healthcare provider should determine why before deciding what should happen next.

Does Amniotic Fluid Change Throughout Pregnancy?

Yes.

Amniotic fluid volume changes as pregnancy progresses. It generally increases through much of pregnancy and then changes as you approach delivery.

That's another reason a single number should never be interpreted without considering gestational age and the rest of the pregnancy.

The clinical context matters just as much as the measurement itself.

When Should You Contact Your Pregnancy Provider?

Contact your OB, midwife, labor and delivery unit, or other pregnancy provider if you experience symptoms such as:

A gush or ongoing leaking of watery fluid, especially if you think your water may have broken.

You should also contact your pregnancy provider promptly if you notice decreased fetal movement once you are at a gestational age when you normally feel your baby's movements.

These concerns need medical evaluation rather than an elective reassurance ultrasound.

Amniotic Fluid and Your Ultrasound at True Ultrasound

At True Ultrasound in Lake Forest, California, we love helping families understand what they are seeing on the ultrasound screen.

During your bonding ultrasound, you may notice your baby floating, stretching, kicking, turning, opening their hands, or moving through pockets of amniotic fluid.

It is amazing to realize how much that fluid is doing behind the scenes to support your growing baby.

However, True Ultrasound provides elective, non-diagnostic pregnancy ultrasounds. If there is concern about too much or too little amniotic fluid, diagnosis and medical management should come from your OB, midwife, diagnostic imaging provider, or maternal-fetal medicine specialist.

Our role is to provide a beautiful bonding experience while always encouraging appropriate prenatal medical care.

A Little World Around Your Baby 🤍

Amniotic fluid may look like a simple dark space on an ultrasound screen, but it is an essential part of your baby's environment.

It protects your baby, provides room to move, contributes to normal development, and gives healthcare providers useful information about the pregnancy.

So the next time you're watching your little one kick and stretch during an ultrasound, remember:

That little world surrounding your baby is doing some very important work. 🤍

📍 True Ultrasound | Lake Forest, California, serving families throughout Orange County.