Constipation during pregnancy can start as early as the second or third month, when hormone levels begin rising significantly. About one in five pregnant women experience it in the first trimester alone, and the problem tends to peak in the second trimester before remaining common through delivery.
The Typical Timeline
A global meta-analysis published in BMC Pregnancy and Childbirth found that 21.1% of pregnant women report constipation in the first trimester, 34% in the second trimester, and 30.3% in the third. That means roughly one in three pregnant women deals with constipation at some point, with the overall global prevalence sitting at 32.4%.
Most women first notice the change somewhere around weeks 8 to 12, though it can creep in earlier. The second trimester is when constipation is most widespread, likely because hormone levels are climbing steeply while the uterus is growing enough to start pressing on surrounding organs. By the third trimester, the baby’s weight adds direct physical pressure on the bowel, which keeps constipation common even as hormone levels plateau.
Why Pregnancy Slows Your Digestion
The main driver is progesterone. Your body produces increasing amounts of this hormone to maintain the pregnancy, and one of its side effects is relaxing smooth muscle throughout your body, including the muscles lining your intestines. Research from the American Physiological Society shows that progesterone works on two fronts: it reduces the chemical signals that trigger intestinal contractions while simultaneously boosting the signals that promote relaxation. The net result is that food moves through your digestive tract more slowly, giving your intestines more time to absorb water from stool. That leaves stool drier, harder, and more difficult to pass.
As the uterus expands, it physically compresses the intestines and further restricts their ability to move things along. This mechanical pressure is why the third trimester often brings the most uncomfortable episodes, even for women who felt fine earlier.
Iron Supplements Get Blamed More Than They Deserve
If you started prenatal vitamins around the same time your constipation appeared, you might assume the iron is the culprit. Many women stop taking their supplements for exactly this reason. But a double-blind, placebo-controlled trial that followed pregnant women from week 20 through delivery found no statistically significant difference in constipation rates between those taking iron supplements and those taking a placebo. At 32 to 36 weeks, 12.9% of women on iron reported constipation compared to 4% on placebo, but this difference was not statistically significant.
The researchers concluded that digestive complaints during pregnancy are mostly caused by the physiological changes of pregnancy itself, not the iron supplement. Stopping your prenatal vitamins is unlikely to resolve constipation and may leave you short on nutrients you and the baby need.
What Actually Helps
Fiber is the single most impactful dietary change. The recommended intake during pregnancy is 28 grams per day, yet fewer than 30% of pregnant women hit that target. Getting there means eating more fruits, vegetables, whole grains, and legumes consistently, not just occasionally. A bowl of oatmeal with berries at breakfast, a salad with beans at lunch, and roasted vegetables at dinner can get you close. If you increase fiber quickly, you may feel bloated at first, so adding it gradually over a week or two works better.
Hydration matters just as much. The standard recommendation is 8 to 10 glasses of water per day during pregnancy. Your body is already using more fluid than usual to support increased blood volume and amniotic fluid, so falling even slightly short can make stool harder. Warm water or warm liquids in the morning can sometimes stimulate a bowel movement on their own.
Physical activity helps keep the intestines moving. Even a 20- to 30-minute walk each day can make a noticeable difference, especially in the second and third trimesters when constipation is most common.
Safe Over-the-Counter Options
When dietary changes aren’t enough, osmotic laxatives (like polyethylene glycol), fiber supplements (like psyllium husk), and probiotics are all considered safe and effective during pregnancy, according to guidelines from the American Academy of Family Physicians. Osmotic laxatives work by drawing water into the intestines to soften stool, while fiber supplements add bulk that encourages the intestines to contract. These are typically the first options a provider will recommend before considering anything stronger.
Stimulant laxatives, which force the intestinal muscles to contract, are generally reserved for short-term use and only after checking with a healthcare provider. Mineral oil is best avoided because it can interfere with nutrient absorption.
Why It’s Worth Managing Early
Chronic straining from constipation is one of the main contributors to hemorrhoids during pregnancy. The combination of increased blood volume, pressure from the uterus on pelvic veins, and repeated straining creates ideal conditions for swollen veins around the rectum. Hemorrhoids affect a significant number of pregnant women and can persist after delivery, so preventing or treating constipation early reduces your risk.
Prolonged constipation can also lead to anal fissures, which are small tears in the lining of the anus caused by passing hard stool. These are painful and can make subsequent bowel movements something you dread, which leads to a cycle of avoidance and worsening constipation. Staying ahead of the problem with fiber, water, and movement from early in the first trimester is far easier than trying to reverse weeks of buildup later.