Hydration During Pregnancy
Your body’s fluid needs increase dramatically during pregnancy. Blood volume rises 30–50%, your kidneys filter 50% more blood, and your body produces amniotic fluid. Yet 67% of pregnant women aren’t meeting hydration recommendations.
Last updated: February 2026
Why Your Body Needs More Water
Pregnancy triggers some of the most significant physiological changes in the human body, and nearly all of them increase fluid demand:
Blood Volume Expansion
Blood volume increases 30–50% to support the placenta and growing fetus. This requires substantially more fluid.
Kidney Workload
Glomerular filtration rate (GFR) increases 50% and renal plasma flow rises up to 80% over non-pregnant levels.
Amniotic Fluid
Your body produces and continuously recycles amniotic fluid. Adequate hydration directly influences amniotic fluid volume.
A review of renal physiology in pregnancy found that the kidneys enlarge, blood pressure drops despite the massive increase in blood volume, and physiologic hydronephrosis (kidney swelling from increased urine flow) develops in up to 80% of pregnant women. Your body’s thirst threshold also drops during pregnancy, signaling that more fluid is needed.
Most Pregnant Women Don’t Know How Much to Drink
A 2024 study of 137 pregnant women found alarming gaps in hydration awareness:
- 63% lacked knowledge of hydration recommendations for pregnancy
- 67% were not meeting their intake targets
- 59% were not tracking fluid consumption at all
The most common barriers were forgetting to drink (47%), not feeling thirsty (47%), and discomfort from increased urination (33%). Despite this, 69% said they would be willing to use a digital tool to track hydration.
Hydration and Amniotic Fluid
Amniotic fluid protects the baby, supports lung development, and allows fetal movement. Low amniotic fluid (oligohydramnios) can lead to complications. Research shows that maternal hydration directly influences amniotic fluid levels.
A controlled trial of 137 women found that hydration therapy nearly doubled amniotic fluid index in just 7 days (from 39.68 mm to 77.70 mm). Women receiving 2,500 mL per day of oral fluids showed greater improvement than those receiving 1,500 mL per day. The study also found reduced cesarean section rates in the hydration group.
A Cochrane review confirmed that simple maternal oral hydration appears to increase amniotic fluid volume and may be beneficial in managing oligohydramnios. Even short-term hydration (2 liters over 2 hours) increased amniotic fluid index in women with low levels.
Morning Sickness, Hyperemesis, and Dehydration
Up to 74% of pregnant women experience nausea and vomiting. For most, it resolves by the second trimester. But for 0.3–3% of pregnancies, it becomes hyperemesis gravidarum, a severe form that can cause dangerous dehydration.
Hyperemesis Gravidarum and Fluid Loss
A study of women presenting to the ER with hyperemesis found they were significantly dehydrated, gaining a mean of 5.6% of body weight from rehydration alone. Urine specific gravity dropped from 1.027 to 1.008 after treatment, confirming clinical dehydration at presentation.
Even mild morning sickness can reduce fluid intake if drinking water triggers nausea. Tips that research supports:
- Sip small amounts frequently rather than drinking large volumes at once
- Room temperature or cold water is often better tolerated than warm
- Track output, not just input: bathroom visit frequency tells you whether you’re staying hydrated despite nausea
- Contact your provider if you cannot keep fluids down for 12+ hours
Pregnancy, Dehydration, and UTI Risk
Pregnant women face elevated UTI risk due to physiological changes: ureteral dilation, urinary stasis, and changes in urine composition. A study of 570 pregnant women found a UTI prevalence of 37.7%, with E. coli causing 65.4% of cases.
Dehydration compounds this risk. Research shows that fewer voids per day, concentrated urine, and inhibited immune function from dehydration all likely contribute to UTI susceptibility. Expert committees recommend adequate fluid intake, frequent voiding, and complete bladder emptying for both prevention and treatment.
For more on the hydration and UTI connection, see our UTI prevention guide.
Breastfeeding: Even Higher Fluid Needs
After delivery, fluid needs increase further. Breast milk is approximately 87% water, and exclusively breastfeeding mothers lose an additional 700 mL of water daily through milk production.
The Institute of Medicine recommends 3.8 liters per day during lactation, up from 3.0 liters during pregnancy. Yet a 2024 study of 529 women found that exclusively breastfeeding mothers had a net water deficit of −475 mL per day, meaning they were chronically under-hydrated compared to non-nursing mothers.
Importantly, a Cochrane review found that forcing extra fluids beyond thirst does not increase milk supply. The goal is not to over-hydrate but to drink enough to avoid deficits. Keep water within arm’s reach during nursing sessions and drink to thirst.
The Simplest Way to Track Hydration During Pregnancy
P Water App tracks hydration through bathroom visits rather than water intake. This approach is especially practical during pregnancy:
- You’re already going more often: increased kidney filtration and uterine pressure mean more bathroom trips. Tap once on the way in.
- No measuring during nausea: when sipping small amounts throughout the day, tracking every sip is impractical. Bathroom frequency captures the result.
- Objective data for your provider: bathroom visit frequency and patterns can be shared with your OB/GYN as a simple voiding diary.
- Apple Watch one-tap logging: especially useful in the third trimester when phone access is less convenient.
- Works postpartum too: continue tracking through breastfeeding when fluid needs are highest.
For related guides, see UTI prevention through hydration and our digital voiding diary guide.
All Research Cited
Simple Hydration Tracking for Pregnancy and Beyond
One tap per bathroom visit. No measuring water, no counting glasses. Track hydration effortlessly through every trimester and into breastfeeding.
Frequently Asked Questions
ACOG recommends 8 to 12 cups (64–96 ounces) per day. The Institute of Medicine sets the Adequate Intake at 3.0 liters of total water daily, including water from food. Your needs may be higher in hot climates, during exercise, or with morning sickness. A practical indicator: aim for 7 or more bathroom visits per day.
Yes. Dehydration has been associated with reduced amniotic fluid (oligohydramnios), which can affect fetal development. A controlled trial found that hydration therapy nearly doubled amniotic fluid levels in 7 days. Dehydration also concentrates urine, increasing UTI risk, and severe dehydration from hyperemesis can require hospitalization.
Your body undergoes massive changes that demand more fluid. Blood volume increases 30–50%, kidneys filter 50% more blood, and your body produces amniotic fluid. Even your thirst threshold changes: pregnancy lowers the set point, which is your body signaling it needs more fluid.
Water does not prevent nausea, but staying hydrated is critical for managing it. Up to 74% of pregnant women experience nausea. With hyperemesis gravidarum, women gain up to 5.6% of body weight from IV rehydration alone. Sip small amounts frequently rather than drinking large volumes at once.
Yes. The IOM recommends 3.8 liters per day during lactation (up from 3.0 during pregnancy). Breast milk is 87% water, and research shows breastfeeding mothers average a −475 mL per day water deficit. Drink to thirst and keep water accessible during nursing. Note: extra fluids beyond thirst do not increase milk supply.
This page summarizes peer-reviewed research for educational purposes. It is not medical advice. If you are pregnant, breastfeeding, or planning a pregnancy, work with your healthcare provider on hydration and nutrition. Hydration apps are wellness tools, not medical devices.