Amniotic Fluid Index Chart: Normal, Low, and High

The fluid around a baby isn’t a fixed amount. It rises and falls through pregnancy, and an ultrasound turns it into a single number in centimetres. Most pregnancies land between roughly 5 and 24 cm, with below 5 cm usually called low and 24 cm or more called high. Because normal values drift downward late in pregnancy, the same number can mean different things at different weeks. And since the measurement shifts from scan to scan, slightly off readings are usually rechecked rather than acted on straight away.

How the Amniotic Fluid Index Is Measured

Your report may say AFI, the amniotic fluid index. The sonographer divides the womb into four quarters, measures the deepest clear pocket of fluid in each, and adds the four numbers together. Some reports instead give the single deepest pocket (SDP, sometimes written MVP), which is just the one deepest pocket anywhere in the womb. That method is quicker, and it is the easier choice in twin pregnancies, where each baby’s sac is measured separately.1Journal of Medical Ultrasound. Amniotic Fluid Volume Assessment Using the Single Deepest Pocket Technique in Bangladesh An AFI of 12 and a deepest pocket of 5 can describe the same healthy pregnancy, so check which method your report used before comparing it to a chart.

The scan itself is the same belly ultrasound as a growth scan, with gel and a probe moved across your abdomen. The sonographer looks for pockets free of baby parts and umbilical cord, and the fluid check adds only a few minutes. The number may be written in cm or mm, so 150 mm equals 15 cm.

Either number is an estimate, not a volume. Nobody measures millilitres directly; pocket depth stands in for the total amount of fluid. The baby’s position can shift pockets from one quarter to another, and a deep pocket squeezed by the baby’s limbs can read smaller than it really is.

AFI Chart by Week of Pregnancy

These reference values come from a large US chart and other studies:

After about 34 weeks AFI gradually drops, and the drop becomes clear after 38 weeks.7PubMed. Curve of amniotic fluid index measurements in low-risk pregnancy In one group of low-risk women, the typical value fell from about 14.6 cm at 34 weeks to about 10.8 cm at 40 weeks.8PubMed Central. Reference Ranges of Amniotic Fluid Index in Late Third Term of Pregnancy: What Should the Optimal Interval between Two Ultrasound Examinations Be? So a reading of 9 cm is unremarkable at 40 weeks but would be on the low side at 30 weeks. Charts differ slightly by population, and many clinics use a broad 5 to 25 cm normal band.

The decline has ordinary causes. As the baby nears birth it swallows more fluid, and the ageing placenta supplies a little less. A gradual drop is expected and isn’t a warning by itself; a sudden drop is what doctors watch for.

To read your own number, find your gestational week first, then compare. A number near the middle of the range needs no action. If it sits near either edge, ask whether a repeat scan is planned. Match AFI to AFI and deepest pocket to deepest pocket, never one against the other.

Your report usually prints the reference range the sonographer used, or the clinic applies a fixed cutoff such as 5 cm, so check which one yours relies on. The lowest and highest normal values are the 5th and 95th percentiles, which means a small share of healthy pregnancies sit just outside the band. A number slightly outside it is a reason for a recheck, not proof that something is wrong.

What Counts as Low Amniotic Fluid

Doctors call low fluid oligohydramnios. It is usually diagnosed at an AFI below 5 cm or a deepest pocket below 2 cm. Nearly every healthy pregnancy has a deepest pocket of at least 2 cm, which makes that a natural floor.9PubMed Central. A Contemporary Amniotic Fluid Volume Chart for the United States: The NICHD Fetal Growth Studies-Singletons

The AFI method, though, labels more women as low. In one trial in labour, it labelled 25% of women as low, versus 8% with the deepest-pocket method.10PubMed. A randomized clinical trial of the intrapartum assessment of amniotic fluid volume: amniotic fluid index versus the single deepest pocket technique Across trials, using AFI more than doubled low-fluid diagnoses and nearly doubled inductions of labour.11PubMed Central. Amniotic fluid index versus single deepest vertical pocket as a screening test for preventing adverse pregnancy outcome Babies did no better for it, with no fewer intensive-care admissions or signs of distress at birth.12PubMed Central. Amniotic fluid index versus single deepest vertical pocket as a screening test for preventing adverse pregnancy outcome If you are told your fluid is low by AFI, it is reasonable to ask whether the deepest pocket is also below 2 cm.

A low label typically leads to a repeat scan within days and monitoring of the baby’s heart rate. Near term it may bring a conversation about induction. The decision weighs your week of pregnancy, the baby’s growth, and the likely cause.

Isolated low fluid means the baby is growing normally and nothing else looks wrong. It is the most common version and the least worrying.

Some questions are worth asking. Which method did the number come from, and what did the other measurement show? A low AFI with a deepest pocket of 2 cm or more is a milder finding than both being low. Might your water have broken? A leak needs a different workup from fluid that is simply on the low side. And when is the repeat scan, and what result would change the plan?

Why Amniotic Fluid Gets Low

From the second trimester, the baby’s skin seals and its urine becomes the main source of the fluid.13GLOWM. Amniotic Fluid: Physiology and Assessment The baby’s lungs add a smaller share, around one sixth.14PubMed Central. Amniotic Fluid: Its Role in Fetal Development and Beyond So anything that cuts the baby’s urine output lowers the fluid.

The main causes follow from that:

Tell your doctor about any painkillers you have taken, and check before taking ibuprofen later in pregnancy. A slow leak can be hard to tell from normal discharge. Leaking fluid is usually watery and keeps coming, and it may increase when you stand or cough. Discharge is usually thicker and doesn’t soak a pad, but these are only rough clues, not a reliable way to tell the two apart. Any suspected leak should be checked the same day.

When the cause is unclear, you can ask whether your baby is growing normally, whether the scan saw the kidneys and bladder, whether your placenta is working well, and whether any medicine you take could play a role.

What Counts as High Amniotic Fluid and Why It Happens

High fluid, called polyhydramnios, is usually diagnosed at an AFI of 24 cm or more or a deepest pocket of 8 cm or more. Fluid stays balanced because near term the baby swallows several hundred millilitres a day, clearing much of what it produces.19PubMed Central. Amniotic Fluid: Its Role in Fetal Development and Beyond If swallowing is impaired, fluid builds up.

Common causes include gestational diabetes, conditions that disturb the baby’s swallowing, and infections.20PubMed Central. Polyhydramnios: Causes, Diagnosis and Therapy A genetic condition in the baby can also be behind it.21nhs.uk. Polyhydramnios (too much amniotic fluid) In many mild cases no cause is found.

Mild high fluid often causes no symptoms. When there are some, they come from the uterus stretching: a belly that measures large for dates, tightness or breathlessness, and swelling and discomfort.

Tests often follow a high reading. These include a glucose test for diabetes and a detailed anatomy scan, and sometimes infection or genetic testing. The results guide how closely you are monitored.

Risks of Fluid That Is Too Low or Too High

Low fluid with poor growth before term carries real risk to the baby.22PubMed. Transabdominal amnioinfusion in preterm pregnancies complicated by fetal growth restriction, oligohydramnios and umbilical cord compression With less cushioning, the cord can be squeezed, slowing the baby’s heart rate. In one large follow-up, children born after isolated low fluid had slightly more neurological hospital stays, 3.7% versus 3.0%.23PubMed. Isolated oligohydramnios and long-term neurological morbidity of the offspring The extra risk is small, and most of these children were fine.

High fluid is linked to preterm labour, early waters breaking, a baby lying in an unusual position, and heavier bleeding after birth.24ABC Law Centers: Birth Injury Lawyers. Polyhydramnios: Excess Amniotic Fluid Risks A baby with a lot of room can turn sideways or feet-first late in pregnancy, which can affect how the birth is planned. If the waters break with a large volume of fluid, the cord can slip down ahead of the baby, which is one reason a team may want you to deliver in hospital if fluid is very high.

Some signs call for prompt action: fewer baby movements, fluid leaking, regular contractions before 37 weeks, or sudden belly growth or breathlessness.

Does Drinking Water Raise Amniotic Fluid

Women who drank 2 litres of water before a repeat scan saw a rise in AFI, of about 2 cm when fluid was low.25PubMed Central. Maternal hydration for increasing amniotic fluid volume in oligohydramnios and normal amniotic fluid volume Drinking works better than IV fluids, and plain fluids beat salty drips.26PubMed Central. An Update on Maternal Hydration Strategies for Amniotic Fluid Improvement in Isolated Oligohydramnios and Normohydramnios: Evidence from a Systematic Review of Literature and Meta-Analysis There is no proof yet that this improves the baby’s outcome.27PubMed Central. Maternal hydration for increasing amniotic fluid volume in oligohydramnios and normal amniotic fluid volume Drinking plenty before a recheck is a safe step, but it is not a treatment for the cause.

Extra water raises the mother’s blood volume, which may let more fluid pass across the placenta and membranes to the baby. That is the usual explanation, though the exact mechanism isn’t settled. The effect is temporary, and a better reading afterward doesn’t show the underlying cause has gone away.

For a recheck, spread the water over the day before and sip rather than gulp to avoid nausea. Keep drinking on the scan day, and tell the sonographer you prehydrated.

What Doctors Do About Abnormal Fluid

Treatment is mostly monitoring and timing of delivery. Monitoring usually means repeat scans weekly or twice weekly, heart rate tracings, and growth checks. If fluid keeps falling at term, a delivery plan follows.

Sometimes fluid is added or drained. In labour, saline can be added to the womb to relieve cord pressure, but doing it routinely offers no advantage over doing it only when the baby’s heart rate drops.28PubMed Central. Prophylactic versus therapeutic amnioinfusion for oligohydramnios in labour Draining fluid for severe high fluid is usually complication-free, though about 1 in 11 procedures led to problems such as placental separation or waters breaking.29PubMed Central. Clinical Outcome and Safety of Amnioreduction in Singleton Pregnancies with Severe Polyhydramnios So draining is kept for severe cases causing symptoms.

Twins differ. Each sac is checked with the deepest pocket. Identical twins sharing a placenta can have one sac very low and one very high. That pattern, under 2 cm and over 8 cm, signals a serious condition that needs a specialist centre.

When the pregnancy is at or near term, persistently low fluid in an otherwise healthy pregnancy is often handled by offering induction rather than waiting. Before term, the team balances the risks of early birth against the risks of leaving the baby in a low-fluid environment, taking growth and heart tracings into account. Your week of pregnancy drives the choice, so the same low reading can lead to monitoring at 32 weeks and an induction offer at 39 weeks.

Why Your Number Can Change Between Scans

The same AFI can vary by about 11% when one person repeats it and about 15% between different sonographers.30PubMed. Intraobserver and interobserver variability of the amniotic fluid index Deepest-pocket readings are harder to reproduce in people with higher body weight.31PubMed. Influence of maternal body mass index on interobserver variability of fetal ultrasound biometry and amniotic-fluid assessment in late pregnancy On a 6 cm reading, a repeat could easily read under 5 cm or over 7 cm. So ask for a repeat scan before decisions are made on a borderline number.32PubMed. Intraobserver and interobserver variability of the amniotic fluid index

Several things push readings around. Baby movement shifts pockets, and pressing the probe harder squeezes them. Hydration on the day matters.