Constipation affects around four in ten pregnancies, and it is one of the few pregnancy symptoms that can start in the first trimester and still be there the week you give birth. Most women get told to eat more fibre and drink more water, which is correct as far as it goes and completely inadequate as a plan.
This guide covers why pregnancy slows your gut down, what to change first, which laxatives are safe and in what order to try them, how to deal with the iron tablets that are often the real culprit, and the small mechanical fixes — including how you sit — that make more difference than most people expect.
The short answer: build up to 25–30g of fibre a day and drink 2–2.5 litres of fluid, because fibre without water makes constipation worse. Walk daily, use a footstool to raise your knees above your hips on the toilet, and go 20–30 minutes after a meal when the bowel is naturally active. If that is not enough, bulk-forming laxatives such as ispaghula husk are the safe first choice, followed by lactulose or macrogol. Avoid castor oil and liquid paraffin. If iron tablets are the trigger, ask about alternate-day dosing or a gentler formulation rather than stopping.
Why pregnancy constipates you
1. Progesterone slows the whole gut
Progesterone relaxes smooth muscle throughout the body to keep the uterus quiet, and the bowel is made of smooth muscle too. The rhythmic contractions that move food along — peristalsis — become slower and weaker from early pregnancy onward. The longer stool sits in the colon, the more water is absorbed out of it, and the harder it gets.
2. Iron supplements
Iron is the single most common trigger, and it is the one most likely to be fixable. Only a fraction of a typical iron dose is absorbed; the rest passes through and slows transit further. If your constipation started within a week or two of beginning a prenatal vitamin or an iron prescription, that is almost certainly your answer.
3. Mechanical pressure in the third trimester
From roughly week 28, the uterus sits directly on the bowel and rectum, physically narrowing the path. This is also when many women reduce their activity, and movement is one of the things keeping the gut going.
4. Everything else pregnancy does to your routine
First-trimester nausea disrupts eating and drinking. Calcium supplements and some antacids bind stool. Pelvic floor changes make it harder to coordinate the muscles involved. And needing to urinate constantly leads a lot of women to quietly drink less, which is exactly the wrong response.
What to change first
Try this first: fibre and fluid together, increased gradually. Going from 15g to 30g of fibre in one day without raising your fluid intake produces a bloated, gassy, still-constipated week. Add roughly 5g of fibre every few days and match it with an extra glass of water each time.
Fibre: 25–30g a day, and the right kind
You need both types. Insoluble fibre (wheat bran, wholegrains, vegetable skins, nuts) adds bulk and speeds transit. Soluble fibre (oats, psyllium, beans, apples, pears, flaxseed) holds water and softens. Most people with pregnancy constipation are short on the soluble kind.
🥣 High-fibre foods that actually work
- Prunes — 4–5 a day, or a small glass of prune juice; the sorbitol content makes them genuinely effective, not folklore
- Kiwi fruit — two a day has decent evidence behind it and is gentler than bran
- Ground flaxseed — a tablespoon stirred into yogurt or porridge
- Oats, beans, lentils and chickpeas — the soluble fibre backbone
- Pears, apples and berries, skins on
- Wholegrain bread and brown rice instead of white
- Vegetables at every meal, cooked as well as raw
- Warm drink first thing — warmth and fluid on an empty stomach stimulate the bowel
Fluid: 2–2.5 litres, and yes you will need the toilet
Bulk-forming fibre without enough water sets like concrete. If you are increasing fibre, fluid is not optional. Water, milk, herbal tea and soup all count; our safe foods guide covers the caffeine limit and which herbal teas to skip.
Movement
A 20–30 minute walk most days measurably speeds gut transit. Swimming and prenatal yoga help too, and yoga in particular includes the gentle twists and forward folds that get things moving. Our safe exercise guide covers what is appropriate at each stage.
How you sit on the toilet matters more than you would think
The human rectum is held at an angle by a muscle called the puborectalis, which is designed to keep you continent while upright. Sitting on a standard toilet only partly releases it. Squatting releases it fully.
🚽 The mechanics
- Footstool under your feet so your knees sit above your hips
- Lean forward, elbows resting on your knees
- Let your abdomen bulge outward and relax rather than clenching
- Breathe out through pursed lips instead of holding your breath and bearing down
- Go 20–30 minutes after a meal, when the gastrocolic reflex is at its strongest
- Never ignore the urge — it passes, and the stool dries out while you wait
- Give it five minutes, then get up and try again later rather than straining
Dealing with iron tablets
If iron is the trigger, the answer is almost never to stop taking it — iron-deficiency anaemia in pregnancy is a real problem with real consequences. Options worth raising with your midwife, GP or pharmacist:
- Alternate-day dosing. Taking iron every other day rather than daily improves the fraction absorbed, because a daily dose raises a hormone called hepcidin that blocks the next day's absorption. Less iron in the gut also means less constipation.
- A different formulation. Iron bisglycinate and ferrous gluconate are generally better tolerated than ferrous sulphate.
- Vitamin C alongside. Taking iron with orange juice or a vitamin C tablet improves absorption, so less passes through.
- Timing. Away from tea, coffee, calcium and dairy, all of which block absorption.
- Check you need the dose you are on. A standard prenatal multivitamin contains iron; if you are also taking a separate prescription, you may be doubling up.
Our prenatal supplements guide covers all seven core supplements and how they interact.
Laxatives, in the order to try them
If diet, fluid and movement have had a fair trial and nothing is happening, laxatives are appropriate — persistent constipation in pregnancy is not something to simply endure. Confirm the specific product and dose with your pharmacist, who can check it against everything else you are taking.
- Bulk-forming (ispaghula husk, methylcellulose, sterculia) — essentially concentrated fibre, first choice in pregnancy, minimally absorbed. Takes two to three days to work and must be taken with plenty of water.
- Osmotic (lactulose, macrogol) — draw water into the bowel to soften stool. Widely used in pregnancy. Lactulose commonly causes wind and bloating for the first few days.
- Stool softeners (docusate) — helpful when the problem is hard stool rather than slow transit, and often used after birth.
- Stimulant (senna, bisacodyl) — make the bowel contract. Kept for short-term use when the above have not worked, and generally avoided close to term.
- Suppositories or micro-enemas (glycerol) — occasional use for a stubborn impacted stool, on advice.
Avoid in pregnancy: castor oil, which can stimulate uterine contractions and is sometimes wrongly recommended for inducing labour; liquid paraffin and mineral oil, which impair absorption of the fat-soluble vitamins A, D, E and K; and prolonged daily use of stimulant laxatives. For the pain of straining or haemorrhoids, paracetamol (acetaminophen) is safe; ibuprofen and other NSAIDs are not after 20 weeks.
Haemorrhoids: the complication to head off
Straining against hard stool, in a body whose veins are already dilated and under pressure from the uterus, is how most pregnancy haemorrhoids start. They affect a large proportion of women in the third trimester and are much easier to prevent than to treat.
If you already have them: keep the stool soft, avoid sitting on the toilet for long stretches, use a cool compress or a witch hazel pad, and ask your pharmacist about a pregnancy-safe topical treatment. They usually improve after birth. Our postpartum recovery guide covers the early weeks, when the first bowel movement after delivery is a widely shared source of dread and is usually far less bad than expected.
When to call your midwife or GP
Call the same day if: you have passed no stool and no wind for several days and your abdomen is distended and painful, you are vomiting, or you are passing more than a streak of blood.
- No bowel movement and no wind for several days, with a swollen, painful abdomen — possible obstruction
- Vomiting alongside constipation
- Rectal bleeding beyond a streak on the paper, or bleeding that keeps recurring
- Severe or constant abdominal pain, as opposed to cramping that comes and goes
- Regular, timeable cramping before 37 weeks — this needs ruling out as preterm labour, not attributing to constipation
- Constipation alternating with diarrhoea, or a persistent change in bowel habit
- Constipation that has not responded to diet changes and an appropriate laxative after a couple of weeks
- Black or tarry stools — usually just the iron, but worth mentioning so it can be confirmed
FAQ — Constipation in pregnancy
Which laxatives are safe during pregnancy?
Bulk-forming laxatives such as ispaghula husk or methylcellulose are first choice and act like concentrated fibre. If those are not enough, osmotic laxatives such as lactulose or macrogol are widely used in pregnancy. Stimulant laxatives such as senna or bisacodyl are usually kept for short-term use when the gentler options fail. Avoid castor oil, which can trigger uterine contractions, and liquid paraffin, which blocks absorption of fat-soluble vitamins. Ask your pharmacist to confirm the product and dose.
Can constipation hurt my baby?
No. Constipation is uncomfortable and can be genuinely painful, but it does not reach or affect the baby. What it can do is cause haemorrhoids and anal fissures from straining, and the cramping it produces can be alarming enough to send people to triage. Treating it is about your comfort and avoiding those complications.
Why do iron tablets cause constipation, and what can I do?
Unabsorbed iron sits in the gut and slows transit, and most prenatal iron doses are far larger than the body can absorb at once. Options your doctor may suggest include taking iron on alternate days rather than daily, which paradoxically improves absorption, switching to a gentler formulation such as iron bisglycinate, or taking it with vitamin C. Do not stop iron on your own if it was prescribed for anaemia.
Is it normal to have cramping with constipation in pregnancy?
Yes. Trapped wind and a loaded bowel produce cramping that is easy to mistake for contractions, and it is one of the more common reasons for a false alarm trip to maternity triage. Constipation cramping tends to shift around, ease after passing wind or opening your bowels, and lack the regular rhythm of contractions. If cramping is regular, timeable or comes with bleeding, get checked.
How much fibre and water do I actually need?
Aim for 25 to 30g of fibre a day and 2 to 2.5 litres of fluid. The two only work together: increasing fibre without increasing fluid reliably makes constipation worse, because bulk-forming fibre needs water to soften. Build fibre up over a week or two rather than all at once, or you will just be bloated as well as constipated.
Does constipation get worse in the third trimester?
Usually yes. Progesterone has been slowing your gut since early pregnancy, and by the third trimester the uterus is also physically compressing the bowel and rectum, iron supplementation is often at its heaviest, and you are moving less. Many women get an early bout in the first trimester too, when progesterone rises sharply and nausea disrupts eating.
Can I strain, or is that dangerous?
Straining will not harm the baby or bring on labour, but it is the direct cause of haemorrhoids and anal fissures, and it puts pressure on an already-loaded pelvic floor. Use a footstool to raise your knees above your hips, lean forward with elbows on knees, and let your abdomen relax outward rather than bearing down hard. If nothing happens in five minutes, get up and come back later.
When should constipation in pregnancy be checked?
Call the same day if you have not opened your bowels or passed wind for several days and your abdomen is swollen and painful, if you are vomiting, if there is more than a streak of blood, or if you have severe or constant abdominal pain. Also get checked for rectal bleeding that does not settle, or constipation alternating with diarrhoea.
Constipation in pregnancy — at a glance
Progesterone slows your gut from early pregnancy, iron tablets slow it further, and the third-trimester uterus physically compresses the bowel. The base plan is 25–30g of fibre and 2–2.5 litres of fluid daily, built up gradually because fibre without water makes things worse, plus daily walking. Add the mechanical fixes: a footstool to raise your knees above your hips, leaning forward, and going 20–30 minutes after a meal. If iron is the trigger, ask about alternate-day dosing or a gentler formulation rather than stopping. Bulk-forming laxatives are the safe first choice, then lactulose or macrogol; avoid castor oil and liquid paraffin. Treat it early — straining is what turns constipation into haemorrhoids.
Inside Baby Novum: the hydration tracker sets a daily water goal calculated from your weight and trimester rather than a generic eight glasses, with reminders through the day, and the supplement tracker keeps your iron timing consistent with an adherence bar you can show at your next appointment.