The Bottom Line

Proper hydration is critical during pregnancy to support additional blood volume, amniotic fluid production, energy needs, kidney performance, avoidance of pregnancy-related side effects, and fetal growth and development.

Pregnant women need to drink more fluid when exercising, when exposed to hot, cold, or dry conditions or high altitude, during an illness, when increasing dietary fiber, and when experiencing nausea and vomiting of pregnancy.

All types of fluid can count toward fluid intake, but women should continue to avoid alcohol and caffeinated beverages which can accelerate dehydration and potentially cause other issues.

Dehydration can lead to serious complications; severe dehydration is a medical emergency and requires immediate medical attention. Women should be aware of the signs and symptoms of dehydration, described below, and seek medical care if dehydration is suspected.

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Pregnant and breastfeeding women need to increase their intake of water and other fluids to meet their bodies' needs. However, the benefits and consequences of hydration and dehydration, as well as the most optimal amount to consume during pregnancy, are not well known and are rarely investigated. Further, research regarding hydration on non-pregnant individuals cannot be completely applied to pregnancy.

Although an extra 300 milliliters per day has been recommended as a good starting point, this recommendation does not take into account unique hydration needs during each trimester, individual body weight and body mass, or physical activity level.

Photo by Maria Di Lorenzo on Unsplash

Water is an essential nutrient critical for metabolism, temperature regulation, tissue maintenance, transporting nutrients and wastes, as well as for optimal absorption of water-soluble vitamins, such as folic acid, vitamin B6, and vitamin B12.

Total body water accumulation during pregnancy is, on average, 6 to 8 liters, which is distributed to the fetus, placenta, amniotic fluid, uterus, breast tissue, blood, and cells. This amount excludes additional fluid that results in swelling.

The body uses additional fluid to assist in the almost 50% increase in blood volume, the production of amniotic fluid and breast milk, and combating fatigue. Water is also continuously exchanged between the developing fetus and its environment.

Although a very small sample, "peak" risk for underhydration may occur starting in the late second trimester.

A study published in July 2021 analyzed 653 urine samples (taken weekly from 14 pregnant women) to better understand variation in hydration status and to identify interventions that improve hydration status during pregnancy.

The researchers found that as the women progressed through pregnancy, they typically became underhydrated during the second trimester and early part of the third trimester (Rosinger et al. 2021).

Amniotic Fluid

The quantity of amniotic fluid at any time in gestation is the product of water exchange between the mother, fetus, and placenta, and can increase or decrease rather quickly at times.

Changes in amniotic fluid volume are usually gradual, however small shifts can occur within hours due to hydration and the mother’s body position and activity.

Hydration can potentially and temporarily increase the amount of amniotic fluid, but more research is needed to determine how much fluid would need to be consumed vs. the amount of extra amniotic fluid that increased water would provide (as well as for intravenous fluid).


Increased thirst is a common symptom of pregnancy.

Human chorionic gonadtropin (HCG) has been implicated as a possible reason for increased thirst in the first trimester, as HCG may lower the body’s threshold for “thirst”, initiating the signal sooner than when not pregnant. This would assist with a woman’s need to drink more fluid in early pregnancy.

Due to the increase in blood volume, which is mostly plasma, pregnancy is considered a state of low serum osmolality.

High osmolality: More electrolytes are in the blood vs. water (dehydrated); Low osmolality: More water is in the blood than electrolytes (overhydrated)

Interestingly, pregnant women’s body systems appear to manage the balance of water, sodium, and blood volume positively, and likely much differently than non-pregnant individuals. The pregnant state does not seem to be sodium/electrolyte depleted despite the increase in body water. However, a lack of hydration can be very dangerous.

Overhydration is usually not a concern during pregnancy, and mild cases may be common.

Overhydration can cause an electrolyte imbalance. However, hydration is already complicated during pregnancy, as the exact relationship between water and sodium during pregnancy is not understood.

Further, exact amounts of necessary fluid intake - and excess fluid intake - is very difficult to determine based on women's varying fluid needs, especially during pregnancy.

Therefore, it is recommended that women simply monitor their fluid intake, drink when appropriate, and recognize the signs and symptoms of dehydration and seek medical care when necessary.


When the normal water content of the body is reduced, it disturbs the balance of minerals (salts and sugar) in the body, which then affects the way it functions.

Nausea and vomiting of pregnancy is one of the main causes of dehydration in the first trimester.

Fever and other illnesses can also cause dehydration; generally, the higher the fever the higher the risk of dehydration. This worsens if the illness also includes diarrhea and/or vomiting.

Exercise without adequate fluid replacement or in hot weather/conditions along with sweating are strong risk factors for dehydration and can cause severe heat injury.

Diabetes insipidus (DI) during pregnancy is characterized by frequent urination and excessive thirst, as the renal tubules (kidneys) fail to conserve water. This condition is assessed to be underdiagnosed since both symptoms are common during pregnancy. However, in DI, both symptoms come on quickly and thirst is very intense.

Symptoms of dehydration include:

Two signs can provide a sense of hydration: skin and urine color.

More serious levels of dehydration can be reflected in reduced skin turgor, with tenting of the skin as a flag for dehydration.

To perform this test, an individual grasps the skin – usually on the forearm – between two fingers to “tent” it up. Normally, the skin returns to normal immediately. If the skin does not rapidly fall flat, it confirms dehydration. 

Another way of monitoring hydration is to check urine color. It should be a pale straw color, and if darker than this, dehydration is likely.


Dehydration can lead to serious complications, including seizures and hypovolemic shock – when low blood volume causes a drop in blood pressure and in the amount of oxygen in the body. Severe dehydration is an emergency and requires immediate medical attention.

Blood volume, blood pressure, and heart rate are closely linked. With a lack of hydration, moving from one position to the other can lead to increased heart rate, a fall in blood pressure and, in some cases, lead to a feeling of faintness.

Dehydration can cause fatigue, headache, and dizziness when moving from one position to another (i.e. lying down to sitting up).

Mild levels of dehydration can also produce disruptions in mood and the ability to concentrate.

Dehydration may also have a role in preterm labor:

Additional hydration through intravenous fluids is a common management technique for the prevention of preterm birth (before 37 weeks), as women in preterm labor often have lower amounts of fluid in their circulation.

It is theorized that extra fluid might somehow slow down contractions by increasing blood flow to the uterus and decreasing pituitary secretion of oxytocin. However, there is very limited information regarding the effectiveness of this technique, and what information does exist does not appear to support it.

It is possible hydration has some effect, but only with false labor, and not when true labor has begun. Dehydration is thought to be a primary initiator of Braxton Hicks contractions, and additional fluid intake is commonly recommended for women suffering from them.

The reason is the same as preterm labor: it is possible that dehydration causes decreased blood flow to the fetus which causes stress, which leads to contractions (note: avoiding fluid intake is not a natural way to "start" labor).

Urinary tract infections (UTIs) can also be problematic. Prolonged or repeated bouts of dehydration can cause urinary tract infections, kidney stones and even kidney failure. UTIs alone can cause serious complications during pregnancy.

Kidneys function more efficiently in the presence of an abundant water supply. If the kidneys economize on water, producing a more concentrated urine, there is a greater cost in energy and more wear on their tissues.


Pregnant women need to monitor their fluid intake and make sure they are drinking enough to remain appropriately hydrated and ease pregnancy-related symptoms,.

There are no established "amounts" of water considered most ideal during pregnancy, as pregnant women have numerous unique aspects of health that can affect the amount of water required for each individual woman.

Plain water is the best beverage of choice to avoid dehydration, but all non-alcoholic drinks can count towards fluid intake (i.e. coconut water and milk).

Plain or sparkling water flavored with fruit can be a "less boring" way to stay hydrated while avoiding sugar and caffeine.

Additional fluid intake is required in hot and cold weather conditions, exercise, illness, and exposure to high altitudes.

Women should avoid drinks with high sugar and caffeine which can contribute to dehydration. However, drinks with electrolytes and small amounts of sugar can be helpful in cases where dehydration is caused by vomiting, diarrhea, or excessive sweating.

Severe dehydration is considered an emergency and requires immediate medical attention. Women should be aware of the signs and symptoms of dehydration, described above, and seek medical care if dehydration is suspected.

Women should read Heat Exposure, Blood Volume, and Kidneys for additional information.


Dehydration can lead to serious complications during pregnancy; severe dehydration is a considered an emergency and requires immediate medical attention. Partners should be aware of the signs and symptoms of dehydration, described above especially if the pregnant women does not notice them, or is unable to describe her symptoms due to her condition.

Partners should also help, remind, and/or make sure that the pregnant woman stays cool and drinks extra fluids during illnesses and exposures to hot, cold, or dry climates.


Dehydration (Mayo Clinic)

Dehydration and Heat Stroke (Johns Hopkins Medicine)


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