Amniotic fluid is the clear pale-yellow water inside the amniotic sac that surrounds the baby through pregnancy. In the first half of pregnancy it is mostly produced by the placenta and fetal membranes, and from around the second trimester onwards it is made largely by the baby itself, through fetal urine and lung secretions, with continuous reabsorption by fetal swallowing and through the membranes. This constant production-and-reabsorption 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 the baby's development. It cushions the baby against sudden movement or pressure from outside, gives space for the baby to move and develop muscle tone and limb shape, regulates temperature in the uterus, and is essential for the development of the fetal lungs and digestive tract because the baby breathes the fluid in and out and swallows it. It also contains 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. This is why the AFI or MVP number is part of every growth scan from the second trimester onwards in standard Indian antenatal care.

Amniotic fluid is measured during an ultrasound scan 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 quadrant, and adds them together for a total in centimetres. The normal range is 5 to 25 centimetres, 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 in the uterus. The normal range is 2 to 8 centimetres. 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 interventions, but AFI is still very widely used and either is acceptable.

These measurements are routinely done at the anomaly scan (18 to 22 weeks) and at every growth scan through the third trimester, and on any extra scan ordered for a specific concern such as reduced fetal movement, suspected leaking of fluid, or high blood pressure. The number is interpreted alongside the rest of the scan (fetal growth, Doppler, placental position) and the clinical picture, not in isolation.

Oligohydramnios is the term for less amniotic fluid than expected for the stage of pregnancy. It is diagnosed when the AFI is less than 5 centimetres or the MVP is less than 2 centimetres. 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).

Around 4 to 8 percent of Indian pregnancies are diagnosed with some degree of oligohydramnios at some point, more commonly in the third trimester and especially after 40 weeks. Mild and isolated low fluid in a baby that is growing well, moving well and has normal Doppler often does not need any intervention beyond increased monitoring; severe or progressive low fluid usually does need active management, sometimes including earlier delivery. The right response depends on the cause and on how the baby is otherwise doing, not just on the number.

The single most common 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 to the baby, the baby produces less urine in response, and the fluid drops. Placental insufficiency is often associated with maternal high blood pressure or preeclampsia (see preeclampsia-pregnancy-bp-india), pre-existing diabetes that is not well-controlled, smoking, and post-dates pregnancy (beyond 40 weeks when the placenta naturally ages).

Fetal causes include problems with the baby's kidneys or urinary tract — because the fetus is the main source of fluid in the second half of pregnancy, any condition that reduces fetal urine production (renal agenesis where one or both kidneys did not form, polycystic kidneys, urinary tract obstruction) results in low fluid, and these are usually picked up at the anomaly scan. Premature rupture of membranes (PROM) — the water bag breaking before labour starts — is another important cause, where the fluid is leaking out and is sometimes mistaken for ordinary discharge.

Maternal causes include significant dehydration (more common in the Indian summer or with vomiting illness), some blood-pressure medications (ACE inhibitors and ARBs are not used in pregnancy), and rarely chronic maternal conditions. The OB will look for the cause through the history, examination and scan, and the treatment depends on what is found.

Polyhydramnios is the term for more amniotic fluid than expected, diagnosed when the AFI is greater than 25 centimetres or the MVP greater than 8 centimetres. 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 percent of pregnancies, and around two-thirds of cases are mild. Mild polyhydramnios in a well-grown baby with a normal anomaly scan and a non-diabetic mother often turns out to have no identifiable cause (called idiopathic polyhydramnios) and usually does not affect outcome significantly. Moderate and severe polyhydramnios more often points to an underlying cause that needs investigation, and the 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 most common identifiable cause of polyhydramnios in Indian pregnancies is gestational diabetes (GDM) — high maternal blood sugar leads to high fetal blood sugar, which leads to increased fetal urine output and therefore more fluid. Any new diagnosis of polyhydramnios is a reason to do an oral glucose tolerance test if it has not been done recently. For more on GDM see Gestational Diabetes in India: OGTT Screening, Indian Diet Plan and Safe Management.

Fetal causes include conditions that prevent the baby from swallowing the fluid normally — esophageal atresia (a blocked food pipe), duodenal atresia, certain neurological conditions that affect 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) increases fluid through the baby's higher cardiac output and is checked through maternal blood tests and fetal Doppler.

In twin pregnancies, twin-to-twin transfusion syndrome (TTTS) in identical twins sharing a placenta produces polyhydramnios in one twin and oligohydramnios in the other, and is a serious condition needing specialist care. Around one-third of polyhydramnios cases turn out to be idiopathic — no identifiable cause is 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, the woman may notice that her belly is smaller than expected for the dates (the OB may also note this on fundal-height measurement at antenatal visits), that fetal movements feel reduced or weaker, or that there is a slow trickle or sudden gush of clear watery fluid from the vagina (suggesting that the membranes have ruptured and the fluid is leaking out).

Polyhydramnios more often produces noticeable symptoms because the uterus becomes larger and more distended. The woman may notice her belly growing rapidly over a short time, marked breathlessness (the high uterus pushes up on the diaphragm), abdominal discomfort or heaviness, leg swelling (from the pressure on the veins returning blood from the legs), heartburn and difficulty eating large meals, and sometimes premature contractions because the over-stretched uterus is more irritable.

Both conditions are most often picked up before the woman notices any symptom, on the routine third-trimester growth scan. The key sign to act on at home, in either condition, is decreased fetal movement (less than 10 kicks in 2 hours after 28 weeks) or sudden gush of fluid, both of which 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 is the main scan to detect fetal causes of abnormal fluid (kidney problems, swallowing problems, structural anomalies). Growth scans in the third trimester (usually one at 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 2500 rupees in private centres and is free or subsidised at government PHC and district hospitals.

When fluid volume is abnormal, the OB will usually order additional tests. A biophysical profile (BPP) combines an ultrasound check of fluid, fetal movement, fetal 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 the baby is doing well or needs delivery. A BPP costs around 1200 to 3000 rupees. 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. Repeat AFI or MVP measurements every few days to a week are common when the fluid is borderline.

For polyhydramnios, the focused workup includes an oral glucose tolerance test (OGTT, around 400 to 1500 rupees) to check for GDM, a detailed repeat anomaly scan, and sometimes blood tests for fetal anaemia causes. 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 the baby is doing. For mild isolated oligohydramnios in a well-grown baby with normal Doppler, the OB will often increase monitoring (twice-weekly NST and weekly scan) without other intervention. Maternal oral hydration with 2.5 to 3 litres of water a day, and in some cases intravenous fluid therapy in the day-care unit, has been shown to transiently raise the AFI in some women and is often tried as a first step. If there is an identifiable underlying cause (high blood pressure, diabetes, infection), it is treated. If the baby is at or near term and the low fluid is moderate to severe, or if there is any sign that the baby is not doing well (abnormal Doppler, abnormal BPP, decreased fetal movement), the OB will usually plan delivery, sometimes by induction and sometimes by caesarean section.

For polyhydramnios, the first step is to treat the underlying cause where one is found — strict glucose control in GDM is often enough to reduce the fluid back into the normal range over a few weeks, and detection and treatment of fetal anaemia where present. Mild idiopathic polyhydramnios in a well-grown baby usually needs only increased monitoring. Severe symptomatic polyhydramnios (marked maternal breathlessness or premature contractions) may need amnioreduction — a procedure done in tertiary care centres where a needle is passed under ultrasound guidance to remove some of the fluid, costing around 15000 to 50000 rupees. Indomethacin to reduce fetal urine production is occasionally used short-term in selected cases before 32 weeks. Delivery is usually planned for term in a centre equipped to manage the potentially 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 these prevents serious complications from being missed. A sudden gush of clear watery fluid from the vagina, or a steady trickle that soaks the underwear without the woman feeling she is passing urine, suggests premature rupture of membranes (PROM) and needs immediate evaluation — both because labour may follow and because the broken membranes increase infection risk if delivery is delayed. Call 108 for the ambulance if you cannot reach the 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 glass of cold water (the standard kick-count test), go to the labour room the same day. This applies to all pregnancies 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 sudden severe headache or visual disturbance (which can suggest preeclampsia) are all reasons for same-day labour-room contact.

Indian hospital options include the nearest government district hospital or medical college (free emergency obstetric care under JSSK and PMSMA), private hospital chains including Apollo Fortis Cloudnine Manipal Max and Rainbow with 24-hour labour rooms, and the 108 ambulance service which is free and provides direct transfer to an obstetric centre.