Dehydration during pregnancy

By trimester

Weeks 1–13

1st trimester

Morning sickness is the most common reason for mild dehydration this early. If fluids aren't staying down, sip small amounts often instead of big gulps, and try ice chips or an electrolyte drink between meals. Vomiting that never lets up and won't let you keep any fluid down is different from typical morning sickness, so consult your healthcare provider if you can't stay hydrated for a full day.

Weeks 14–27

2nd trimester

Your blood volume is expanding fast now, so your body needs more fluid than it did before pregnancy. Drink water steadily through the day instead of catching up all at once, and reach for an electrolyte drink on hot days or after exercise. Pale yellow urine is a good sign you're keeping up, while dark yellow or amber urine means it's time to drink more.

Weeks 28–birth

3rd trimester

Dehydration now can bring on more noticeable Braxton Hicks tightening or real contractions, since low fluid levels make your uterus more irritable. Keep water and an electrolyte drink within reach, especially in hot weather or after a long day on your feet. If lying down on your side and drinking fluids doesn't ease contractions within an hour, call your provider or head to labor and delivery.

What does the evidence show for dehydration?

• When nausea and vomiting never let up, it's called hyperemesis gravidarum, and it can cause real dehydration, weight loss, and a faint, lightheaded feeling. 1
• Sipping small amounts of cold or partly frozen fluids through the day, working up to about 8 cups, is one of the easiest ways to stay ahead of dehydration when nausea makes eating and drinking hard. 2
• Dehydration can make your uterus more irritable and trigger contractions, so drinking fluids is one of the first steps providers try when early contractions or preterm labor symptoms show up. 3
• Pregnancy raises your daily potassium target to about 2,900 mg, one of the key electrolytes that works with water to keep your fluid balance and muscles running smoothly. 4
• Your magnesium needs climb too, to roughly 350 to 360 mg a day, since this electrolyte supports normal muscle and nerve function, including in your uterus. 5
• Dehydration serious enough to need medical evaluation can show up as dizziness on standing, dry mucous membranes, a fast heartbeat, or being unable to tolerate any oral intake, and losing 5 percent or more of prepregnancy weight is one marker providers use when deciding IV fluids are needed. 6

When should I call my provider about dehydration?

Signs that dehydration has moved beyond something a few glasses of water will fix include feeling dizzy or faint when you stand up, a dry mouth that does not ease with sipping, a fast heartbeat, or being unable to keep any food or fluid down at all. Losing 5 percent or more of your prepregnancy weight is another marker providers use to decide dehydration from nausea and vomiting needs same-day evaluation and possibly IV fluids rather than home measures alone. If you are ever unsure which side of the line you are on, make the call. Obstetric teams handle these check-ins as routine, not as overreacting.