Polyhydramnios: Too Much Amniotic Fluid

Polyhydramnios (also known as "hydramnios") is the medical term for a pregnancy complication in which there is too much amniotic fluid inside the womb. Polyhydramnios is uncommon, occurring in about 1.5 out of every 100 pregnancies.

What is Polyhydramnios?

Amniotic fluid is the life-giving liquid substance that surrounds the fetus inside the womb. This fluid plays a critical role in the process of fetal gestation. The fetus not only floats around in amniotic fluid but actually inhales and exhales it. Amniotic fluid facilitates fetal growth, develops the lungs, insulates the womb from heat loss and acts as a protective cushion around the baby.

In a normal pregnancy the amount of amniotic fluid should stay within certain ranges. The normal volume of amniotic fluid varies based on the size of the baby and the stage of gestation but should be somewhere between a minimum of 500 ml and a maximum of 1000 ml. The normal amniotic fluid level peaks in the 34th week of pregnancy when it should average around 800 ml. When the baby is full term the level should drop down to around 600 ml.

Polyhydramnios is a condition that occurs when the volume of amniotic fluid exceeds normal levels. Polyhydramnios is diagnosed in approximately 1% of all pregnancies which makes it uncommon but not rare. Most of the time polyhydramnios is mild and is not harmful to the baby. However, moderate to severe cases of acute polyhydramnios (in which amniotic fluid volume is high) can trigger major complications with pregnancy and birth and pose a health risk to the baby.

Polyhydramnios Symptoms

PregnancyThe majority of polyhydramnios cases are classified as "mild" and only involve a small amount of excess amniotic fluid which builds up in the later stages of pregnancy. Mild polyhydramnios is defined as a value of 8–11 cm as opposed to 16 cm to 86 cm with severe polyhydramnios.  Mild polyhydramnios is generally innocuous and rarely causes any significant complications with the pregnancy. There are typically no clinical symptoms associated with mild polyhydramnios.

The more excess amniotic fluid there is the greater the severity of polyhydramnios. The reason for this is fairly simply. As the volume of excess amniotic fluid inside the mother's womb continues to build it starts to swell in size (like a water balloon with too much water). This creates abnormal pressure both inside the uterus and outside on the internal organs surrounding it.

Moderate or serious cases of polyhydramnios usually do generate a number of noticeable physical symptoms which often include:

  • Chronic swelling in the feet, ankles and legs
  • Respiratory distress (shortness of breath, discomfort when breathing)
  • Difficult or discomfort with urination and/or cons
  • Swollen vulva
  • Continuous heartburn
  • Abdominal discomfort

Polyhydramnios may also present clinical symptoms that doctors can identify on examination. These include large uterine measurements and difficulty feeling the baby or tracking its fetal heart rate inside the womb.

Most cases of polyhydramnios occur later on in pregnancy, but the condition can occur as early as week 16-17. The earlier polyhydramnios occurs during pregnancy the more potentially serious and concerning it is likely to be.

Causes of Polyhydramnios

Mild polyhydramnios occurring in the late stages of pregnancy is often the result of natural amniotic fluid buildup that some mothers experience and others do not. More serious cases of polyhydramnios tend to develop earlier in pregnancy and are often triggered by or associated with certain known causes including:

  • Birth Defect: during pregnancy the baby will regularly swallow amniotic fluid, break it down and discharge it through urination. This process helps keep fluid levels within normal ranges. However, there are several congenital birth defects which may prevent the baby from swallowing or digesting amniotic fluid which can result in excess fluid levels. (Polyhydramnios itself is not a birth defect by definition.)
  • Maternal Diabetes Mellitus: high levels of glucose in the mother's bloodstream can trigger a buildup of excess amniotic fluid. High glucose levels can occur if the mother had diabetes before pregnancy or develops gestational diabetes during pregnancy.
  • TTTS: TTTS stands for Twin-to-Twin Transfusion Syndrome which a complication with identical twins in which one twin is getting more blood flow than the other. TTTS has been linked to excess amniotic fluid.
  • Fetal Anemia: polyhydramnios can occur if the baby does not have adequate red blood cell levels - a condition known as fetal anemia.
  • Rh-factor: If mother and baby have incompatible Rh-negative and Rh-Positive blood types the baby may develop a condition called Rh-factor. This is a special type of fetal anemia which can also lead to excess amniotic fluid.
Is Polyhydramnios Dangerous to the Baby?

Many mothers-to-be reading this want to know if they can still have a healthy baby with polyhydramnios.  The answer is of course you can and almost certainly will.  Most of the time polyhydramnios is mild and does not cause any notable complications or increased risks in the pregnancy. Even children who are transferred to neonatal intensive care after birth from complications from too much amniotic fluid still typically fare very well. 

But, and there is a but, in cases of severe polyhydramnios, there is significant risk of serious pregnancy and childbirth complications. The most significant complications associated with polyhydramnios include:

  • Prematurity: excess amniotic fluid levels can trigger pre-term labor and increase the chances of a baby being born prematurely. This is a concern because prematurity greatly increases a baby's risk of various health problems and complications including birth injuries.
  • Fetal Macrosomia: polyhydramnios is commonly associated with excess fetal growth which can develop into fetal macrosomia. Macrosomic babies cannot be safely delivered via vaginal delivery.
  • Placental Abruption: this is a very dangerous complication in which the placenta prematurely separates from the wall of the uterus before the baby is ready for delivery. This creates an emergency event that must be quickly diagnosed and managed to avoid injury to the baby.
  • Fetal Malposition: when there is too much amniotic fluid in the womb it has a tendency to cause malposition of the fetus (e.g., breech, transverse, etc.) which can complicate vaginal delivery.
  • Umbilical Cord Prolapse: this is one of the most dangerous delivery complications which occurs when the umbilical cord drops down into the birth canal in front of the baby during delivery, creating a major risk of oxygen deprivation.
Polyhydramnios Studies and Research

Bart, Yossi, et al.: "The effect of polyhydramnios on the success of trial of labor after cesarean delivery (TOLAC): A retrospective cohort." European Journal of Obstetrics & Gynecology and Reproductive Biology 253 (2020): 187-190. (This study looked at polyhydramnios’ effect on a trial of labor after cesarean’s success rate. The researchers found that 69.2 percent of TOLACs involving polyhydramnios were successful compared to 85.8 percent of TOLACs that did not involve polyhydramnios. They also found that polyhydramnios was associated with higher C-section rates. However, there was no difference in uterine rupture rates. The researchers concluded that physicians should consider this information when counseling patients.)

Erfani, Hadi, et al. "Amnioreduction in cases of polyhydramnios: Indications and outcomes in singleton pregnancies without fetal interventions." European Journal of Obstetrics & Gynecology and Reproductive Biology 241 (2019): 126-128. (This study looked at outcomes that followed amnioreductions in singleton pregnancies. The researchers found that, following these procedures, singleton pregnancies were associated with lowered rates of preterm deliveries, membrane ruptures, placental abruptions, sepsis, and newborn deaths.)

Katsura, Daisuke, et al. "Relationship between higher intra-amniotic pressures in polyhydramnios and maternal symptoms." European Journal of Obstetrics & Gynecology and Reproductive Biology 235 (2019): 62-65. (This study looked at the intra-amniotic pressure difference among symptomatic and asymptomatic polyhydramnios patients. The researchers found that symptomatic patients had higher intra-amniotic pressure levels than asymptomatic patients. They concluded healthcare providers should monitor intra-amniotic pressure levels to avoid potential pressure change harm.)

Khan, Sarwat, and Jennifer Donnelly.: "Outcome of pregnancy in women diagnosed with idiopathic polyhydramnios." Australian and New Zealand Journal of Obstetrics and Gynaecology 57.1 (2017): 57-62. (This study looked at the relationship between polyhydramnios and adverse pregnancy outcomes. The researchers found that polyhydramniotic mothers were associated with higher C-section, fetal distress, and NICU admission rates. They concluded that these effects necessitate close monitoring of polyhydramniotic pregnancies.)

Khazaei, Salman, and Ensiyeh Jenabi.: "The association between polyhydramnios and the risk of placenta abruption: a meta-analysis." The Journal of Maternal-Fetal & Neonatal Medicine 33.17 (2020): 3035-3040. (This study looked at an association between polyhydramnios and placental abruptions. The researchers’ data came from reviews and meta-analyses. They found that polyhydramnios increased the placental abruption risk.)

Kornacki, Jakub, et al.: "Polyhydramnios—frequency of congenital anomalies in relation to the value of the amniotic fluid index." Ginekologia Polska 88.8 (2017): 442-445. (This study looked at the association between amniotic fluid levels and fetal anomalies. The researchers found that high amniotic fluid levels increased the fetal anomalies incidence. Gastrointestinal tract abnormalities were the most commonly reported anomaly.)

Zeino, S., et al.: "Delivery outcomes of term pregnancy complicated by idiopathic polyhydramnios." Journal of Gynecology Obstetrics and Human Reproduction 46.4 (2017): 349-354. (This study looked at delivery characteristics and mode in polyhydramniotic pregnancies. The researchers found that polyhydramniotic pregnancies were more likely to result in C-sections, prolonged labor, non-vertex presentations, and amniotomies compared to non-polyhydramniotic ones.)