Amniotic Fluid in Pregnancy: Low (Oligohydramnios) & High (Polyhydramnios)

• Amniotic fluid cushions your baby, lets them move, and is essential for lung and gut development — its volume is an indirect signal of placental and fetal health.
• It is measured on ultrasound as the AFI (normal 5–25 cm) or the single deepest pocket / MVP (normal 2–8 cm); many Indian centres now prefer MVP because it causes fewer false alarms.
• Oligohydramnios (low fluid) affects roughly 4–8% of pregnancies; mild isolated low fluid in a well-grown, well-moving baby often needs only closer monitoring.
• Polyhydramnios (high fluid) affects about 1–2% of pregnancies; the commonest treatable cause in India is gestational diabetes, so a glucose test is standard.
• The number is interpreted alongside fetal growth, Doppler and movement — not in isolation. A high number is not extra reassurance, and a low number is not automatically a disaster.
• Sudden gush or trickle of watery fluid, or reduced fetal movements after 28 weeks, both need same-day labour-room contact.

Amniotic fluid is the clear, pale-yellow water inside the amniotic sac that surrounds your baby through pregnancy. In the first half of pregnancy it comes mostly from the placenta and fetal membranes. From around the second trimester it is made largely by the baby — through fetal urine and lung secretions — with continuous reabsorption as the baby swallows it and through the membranes. This constant make-and-reabsorb cycle keeps the volume in a healthy range that rises through pregnancy, peaks around 34 to 36 weeks at roughly 800 to 1000 millilitres, and then gradually reduces towards term.

The fluid does several jobs that matter for development. It cushions your baby against sudden pressure from outside, gives space to move and build muscle tone and limb shape, keeps the temperature in the uterus steady, and is essential for the developing lungs and digestive tract because your baby breathes the fluid in and out and swallows it. It also carries antibodies that protect against infection.

Because the volume depends on a working placenta, a baby with normal kidneys and lungs, and intact membranes, the amount of fluid is a useful indirect signal of fetal and placental health. That is why the AFI or MVP is part of every growth scan from the second trimester onwards in standard Indian antenatal care, and one of the numbers parents most often ask about.

Amniotic fluid is measured during an ultrasound using one of two methods. The Amniotic Fluid Index (AFI) divides the uterus into four quadrants, measures the deepest vertical pocket of fluid in each, and adds them into a total in centimetres. The normal range is 5 to 25 cm, with 8 to 18 considered comfortably normal through most of the third trimester.

The Maximum Vertical Pocket (MVP), also called the Single Deepest Pocket (SDP), measures only the single deepest vertical pocket of clear fluid. Its normal range is 2 to 8 cm. Many Indian centres now prefer the MVP because the evidence shows it leads to fewer false-positive diagnoses of low fluid — and therefore fewer unnecessary inductions and caesareans — but AFI is still very widely used and either is acceptable.

These measurements are routinely done at the anomaly (TIFFA) scan at 18 to 22 weeks and at every third-trimester growth scan, plus any extra scan ordered for a specific concern such as reduced fetal movement, suspected leaking, or high blood pressure. The fluid number is read alongside the rest of the scan — fetal growth, Doppler, placental position — and your clinical picture, never in isolation.

Oligohydramnios means less amniotic fluid than expected for the stage of pregnancy. It is diagnosed when the AFI is below 5 cm or the MVP is below 2 cm. Severity matters: an AFI of 3 to 5 (or MVP 1 to 2) is mild, an AFI of 2 to 3 is moderate, and an AFI below 2 with no measurable pocket is severe — sometimes called anhydramnios when there is essentially no fluid at all.

Around 4 to 8% of Indian pregnancies are diagnosed with some degree of oligohydramnios at some point, more often in the third trimester and especially after 40 weeks. Mild, isolated low fluid in a baby that is growing well, moving well and has normal Doppler often needs nothing beyond closer monitoring, and frequently improves on a repeat scan a few days later. Severe or progressive low fluid usually does need active management, sometimes including earlier delivery. The right response depends on the cause and on how your baby is doing — not just the number.

The single commonest cause of low fluid in Indian pregnancies, especially in the third trimester, is placental insufficiency — the placenta is not delivering enough blood, oxygen and nutrients, so the baby makes less urine and the fluid drops. This often goes hand-in-hand with intrauterine growth restriction (IUGR) and is commonly linked to maternal high blood pressure or Preeclampsia in Pregnancy: High BP, Warning Signs and Care, poorly controlled diabetes, smoking, and post-dates pregnancy beyond 40 weeks when the placenta naturally ages.

Fetal causes centre on the baby's urine output, since the fetus is the main source of fluid in the second half of pregnancy. Conditions that reduce fetal urine — renal agenesis (one or both kidneys did not form), polycystic kidneys, or urinary-tract obstruction — lower the fluid, and are usually picked up at the anomaly scan. Premature rupture of membranes (PROM), where the water bag breaks before labour, is another key cause; the fluid leaks out and is sometimes mistaken for ordinary discharge. If you are unsure, our guide to what water breaking feels like can help you tell the difference.

Maternal causes include significant dehydration (more common in the Indian summer or with a vomiting illness) and certain blood-pressure medications — ACE inhibitors and ARBs are not used in pregnancy. Your OB looks for the cause through your history, examination and scan, and the treatment depends on what is found.

Polyhydramnios means more amniotic fluid than expected, diagnosed when the AFI is above 25 cm or the MVP above 8 cm. Severity matters here too: an AFI of 25 to 29.9 (or MVP 8 to 11) is mild, 30 to 34.9 (MVP 12 to 15) is moderate, and 35 or more (MVP above 16) is severe.

Polyhydramnios affects around 1 to 2% of pregnancies, and about two-thirds of cases are mild. Mild polyhydramnios in a well-grown baby with a normal anomaly scan and a non-diabetic mother often has no identifiable cause — called idiopathic polyhydramnios — and usually does not affect the outcome much. Moderate and severe polyhydramnios more often points to an underlying cause, so your OB will order a focused workup: usually a glucose tolerance test, a detailed re-look at fetal anatomy, and in twin pregnancies an evaluation for twin-to-twin transfusion syndrome.

The single commonest identifiable cause of polyhydramnios in Indian pregnancies is gestational diabetes (GDM) — high maternal blood sugar leads to high fetal blood sugar, which increases fetal urine output and therefore fluid. Any new diagnosis of polyhydramnios is a reason to do an oral glucose tolerance test if one has not been done recently. Our full guide to gestational diabetes screening and the Indian diet plan walks through what good control looks like.

Fetal causes include conditions that stop the baby swallowing fluid normally — oesophageal atresia (a blocked food pipe), duodenal atresia, certain neurological conditions affecting swallowing, and structural anomalies of the face or neck. The anomaly scan and a focused repeat scan look for these. Severe fetal anaemia — from Rh isoimmunisation, parvovirus infection or other causes — raises fluid through the baby's higher cardiac output; this is checked through maternal blood tests and fetal Doppler. If you are Rh-negative, see why the anti-D injection and antibody screening matter.

In twin pregnancies, twin-to-twin transfusion syndrome (TTTS) in identical twins sharing one placenta produces polyhydramnios in one twin and oligohydramnios in the other — a serious condition needing specialist fetal-medicine care. Around one-third of polyhydramnios cases turn out to be idiopathic, with no cause found despite a proper workup, and these usually have good outcomes.

Oligohydramnios often has no symptoms and is picked up on a routine scan. When it does cause noticeable changes, you may find your belly is smaller than expected for your dates (your OB may also note this as a low fundal height at antenatal visits), that movements feel reduced or weaker, or that there is a slow trickle or sudden gush of clear watery fluid from the vagina — suggesting the membranes have ruptured and fluid is leaking out.

Polyhydramnios more often produces noticeable symptoms because the uterus becomes larger and more stretched. You may notice your belly growing fast over a short time, marked breathlessness (the high uterus pushes up on the diaphragm), abdominal heaviness or discomfort, leg swelling from pressure on the veins draining the legs, worsening heartburn and difficulty eating large meals, and sometimes early contractions because the over-stretched uterus is more irritable.

Most often, though, both conditions are spotted before you notice anything, on the routine third-trimester growth scan. The key sign to act on at home, in either condition, is decreased fetal movement (fewer than 10 kicks in 2 hours after 28 weeks) or a sudden gush of fluid — both need same-day OB contact.

The diagnosis is made on ultrasound. The anomaly scan at 18 to 22 weeks is the first detailed look at fetal anatomy and fluid volume, and the main scan to detect fetal causes of abnormal fluid (kidney problems, swallowing problems, structural anomalies). Growth scans in the third trimester — usually one around 28 to 32 weeks and one at 34 to 36 weeks, with extra scans for any concern — measure AFI or MVP and check fetal growth and Doppler. A typical Indian USG growth scan costs around ₹800 to ₹2,500 in private centres and is free or subsidised at government PHCs and district hospitals.

When the fluid is abnormal, your OB will usually order more tests. A biophysical profile (BPP) combines an ultrasound check of fluid, movement, breathing movements and tone with a non-stress test (NST) of the fetal heart pattern, gives a score out of 10, and helps decide whether your baby is doing well or needs delivery; a BPP costs around ₹1,200 to ₹3,000. A fetal Doppler ultrasound checks blood flow in the umbilical artery, middle cerebral artery and ductus venosus and is the key test for placental insufficiency — see fetal Doppler monitoring for how it guides decisions. Repeat AFI or MVP every few days to a week is common when the fluid is borderline. Our guide to fetal monitoring with NST and BPP explains how often these are done.

For polyhydramnios, the focused workup includes an oral glucose tolerance test (OGTT, around ₹400 to ₹1,500) for GDM, a detailed repeat anomaly scan, and sometimes blood tests for causes of fetal anaemia. ASHA workers and ANMs at the PHC monitor fundal height and basic antenatal parameters free of cost in the public system, and refer to the district or tertiary hospital for any concern.

Treatment depends on whether the fluid is low or high, the severity, the cause, and how your baby is doing. For mild isolated oligohydramnios in a well-grown baby with normal Doppler, your OB will often simply increase monitoring (twice-weekly NST, weekly scan) without other intervention. Good maternal Water Intake in Pregnancy: How Much to Drink (India Guide) — about 2.5 to 3 litres of fluid a day, and sometimes intravenous fluids in the day-care unit — has been shown to transiently raise the AFI in some women and is often tried first. Any underlying cause (high blood pressure, diabetes, infection) is treated. If your baby is at or near term and the low fluid is moderate to severe, or there is any sign the baby is not doing well (abnormal Doppler, low BPP, reduced movement), your OB will usually plan delivery — sometimes by induction of labour and sometimes by caesarean.

For polyhydramnios, the first step is to treat the underlying cause where one is found — strict glucose control in GDM is often enough to bring the fluid back into normal range over a few weeks, and fetal anaemia is treated where present. Mild idiopathic polyhydramnios in a well-grown baby usually needs only closer monitoring. Severe symptomatic polyhydramnios — with marked breathlessness or preterm contractions — may need amnioreduction, a procedure in tertiary centres where a needle is passed under ultrasound guidance to remove some fluid, costing around ₹15,000 to ₹50,000. Indomethacin to reduce fetal urine output is occasionally used short-term before 32 weeks. Delivery is usually planned for term in a centre equipped to manage the raised risks of cord prolapse and postpartum haemorrhage.

Several signs in the context of abnormal amniotic fluid need same-day labour-room contact, and being clear on them prevents serious problems being missed. A sudden gush of clear watery fluid, or a steady trickle that soaks your underwear without you feeling you are passing urine, suggests premature rupture of membranes (PROM) and needs immediate evaluation — both because labour may follow and because broken membranes raise infection risk if delivery is delayed. Call 108 for an ambulance if you cannot reach hospital quickly.

Decreased fetal movement is the other key red flag: count kicks daily after 28 weeks, and if there are fewer than 10 movements in 2 hours despite lying on your side after a meal and a cold drink, go to the labour room the same day. This applies to every pregnancy but is especially important if you already know the fluid is abnormal. Severe persistent breathlessness, severe abdominal pain, contractions before 37 weeks, vaginal bleeding, fever, or a sudden severe headache or visual disturbance (which can signal preeclampsia) are all reasons for same-day labour-room contact.

Your options include the nearest government district hospital or medical college (free emergency obstetric care under JSSK and PMSMA), private hospital chains such as Apollo, Fortis, Cloudnine, Manipal, Max and Rainbow with 24-hour labour rooms, and the free 108 ambulance service, which transfers you directly to an obstetric centre. Keeping a printed birth-and-emergency plan handy makes these decisions calmer when they come up.

• ACOG Practice Bulletin: Antepartum Fetal Surveillance
• ISUOG Practice Guidelines: ultrasound assessment of fetal biometry and growth
• NHS: Polyhydramnios (too much amniotic fluid)
• MSD Manual: Oligohydramnios and Polyhydramnios
• Ministry of Health and Family Welfare (India): Pradhan Mantri Surakshit Matritva Abhiyan (PMSMA)