Diarrhea during pregnancy is common and usually harmless. Hormonal shifts, dietary changes, new supplements, and the physical pressure of a growing uterus on your digestive tract can all loosen your stools at various points across all three trimesters. In most cases, it resolves on its own within a day or two without affecting your baby.
Hormonal Changes That Affect Your Gut
Pregnancy hormones reshape how your entire digestive system works. Progesterone, which rises sharply in early pregnancy, slows down the muscles that move food through your intestines. This is the well-known cause of pregnancy constipation, but the effect isn’t always consistent. Fluctuations in hormone levels can swing things the other direction, speeding up digestion and pulling more water into your intestines, which results in loose or watery stools.
Estrogen and other hormones also change how sensitive your gut is to certain foods. Something you tolerated fine before pregnancy might suddenly trigger cramping or urgency. This is especially noticeable in the first trimester, when hormone levels are shifting most dramatically, and again in the third trimester as your body prepares for labor.
Prenatal Vitamins and Diet Shifts
Your prenatal vitamin is a surprisingly common culprit. Iron, one of the key ingredients, is well known for causing gastrointestinal side effects including diarrhea, belly pain, and nausea. Magnesium, another frequent addition, draws water into the intestines and can have a laxative effect at higher doses. If your diarrhea started around the same time you began a new supplement, that connection is worth exploring with your provider. Switching brands or taking your vitamin with food sometimes helps.
Many people also overhaul their diet after learning they’re pregnant, eating more fiber-rich fruits and vegetables, adding dairy for calcium, or cutting out caffeine. Any sudden dietary change can disrupt your digestion. Increased dairy intake, in particular, can trigger diarrhea if you have even mild lactose sensitivity, something that can emerge or worsen during pregnancy.
Food Sensitivities and Foodborne Illness
Pregnancy alters your immune system in ways that make you more vulnerable to foodborne infections. Salmonella from undercooked eggs or meat and listeria from deli meats, soft cheeses, or unwashed produce are the biggest concerns. Diarrhea from a standard stomach bug is unpleasant but typically resolves without lasting harm. Listeria is different.
Listeria infection affects roughly 1 in 25,000 pregnant women each year in the United States, according to the CDC. What makes it dangerous is that you might not feel very sick yourself, yet the bacteria can cross the placenta and reach your baby. Among pregnant women who do develop listeria infection, about 1 in 4 experience pregnancy loss or lose their baby shortly after birth. If you develop diarrhea along with fever, muscle aches, or flu-like symptoms, and you’ve recently eaten high-risk foods, contact your provider promptly.
Diarrhea in Late Pregnancy
Loose stools in the third trimester have an additional possible explanation: your body getting ready for labor. In the days or hours before labor begins, your body naturally clears out the digestive system. The same chemical signals that help soften and open the cervix also stimulate the muscles in your bowels, which can cause increased bowel movements or outright diarrhea. This is a well-recognized pre-labor sign, particularly if it comes alongside other signals like lower back pain, pelvic pressure, or the loss of your mucus plug.
That said, not everyone who gets diarrhea at 37 or 38 weeks goes into labor the next day. It can happen days or even a week or more before contractions start. If you’re past 37 weeks and notice a pattern of loose stools along with regular tightening in your abdomen, it’s worth timing those sensations.
Why Dehydration Matters More During Pregnancy
The main risk of diarrhea during pregnancy isn’t the diarrhea itself. It’s dehydration. Your blood volume increases by nearly 50% during pregnancy, and your body needs significantly more fluid than usual to support that. Losing fluid through frequent loose stools depletes those reserves faster than you might expect.
Signs of dehydration to watch for include dark yellow urine or noticeably less urine than usual, a dry mouth, headaches, dizziness, and a rapid heart rate. Confusion or fainting are more serious signs that need immediate attention. The simplest counter is to drink more fluids than you think you need, especially water, broth, or an oral rehydration solution. Avoid sugary drinks, which can make diarrhea worse.
What You Can Safely Take
Most over-the-counter stomach remedies are off-limits during pregnancy. Bismuth subsalicylate (the active ingredient in Pepto-Bismol) is not considered safe. According to Cleveland Clinic guidelines, the only pregnancy-safe anti-diarrheal medication is loperamide (Imodium), and even that comes with restrictions: it should not be used during the first trimester, and you shouldn’t take it for more than 24 hours.
For most episodes, the better approach is dietary. Stick to bland, easy-to-digest foods like rice, bananas, toast, and applesauce. Avoid greasy, spicy, or high-fiber foods until things settle. Small, frequent meals are easier on your system than large ones. Probiotic-rich foods like yogurt may also help restore balance in your gut, though results vary from person to person.
Signs That Need Medical Attention
Most pregnancy diarrhea is a nuisance, not an emergency. But certain combinations of symptoms warrant a call to your provider or a trip to the hospital:
- Fever of 100.4°F or higher, which can signal an infection that needs treatment
- Blood or mucus in your stool, or stools that appear black and tarry
- Diarrhea lasting more than 48 hours without improvement
- Signs of dehydration like dizziness, confusion, fainting, or inability to keep fluids down for more than 8 hours
- Severe abdominal pain that is sharp, sudden, or getting worse over time, rather than the mild cramping that often accompanies loose stools
If you’re earlier than 37 weeks and experiencing diarrhea with regular cramping or tightening, it’s worth contacting your provider to rule out preterm labor, since dehydration and intestinal contractions can sometimes trigger uterine contractions.