Constipation in Pregnancy
Why it happens from the first trimester, what iron has to do with it, what is usually used, and the link to piles nobody mentions until it is too late.
Part of the Complete Constipation Guide.
Key fact: Constipation in pregnancy is caused by the pregnancy itself — progesterone slows the gut from early on — and is then commonly worsened by iron supplements. It is not something you have done wrong, and it is very treatable.
Why pregnancy causes it
Three things stack up, and they arrive at different points.
Progesterone
Relaxes smooth muscle throughout the body, including the bowel wall. Transit slows from the first trimester, before there is any physical pressure.
More water absorbed
Slower transit means the bowel has longer to take water out of the stool, which makes it harder.
Pressure later on
In the third trimester the growing uterus presses on the rectum and reduces the space available.
Add reduced activity, nausea limiting what you eat and drink in early pregnancy, and iron supplements, and it becomes one of the most common complaints of pregnancy.
The iron problem
Iron supplements are a well-recognised cause of constipation, and in pregnancy they are frequently the tipping point — someone managing until they start iron for anaemia, and struggling from that week on.
- Do not simply stop the iron. It is being taken for a reason, and anaemia in pregnancy matters
- Do raise it. There are options: a different iron salt, a lower dose, or alternate-day dosing, which is increasingly used and is often as effective
- Take vitamin C or orange juice with it to aid absorption, and avoid tea or coffee at the same time
- Expect dark stools. Iron turns stools black, which is normal. Black tarry stools with a strong smell are different and need urgent assessment
What to try first
| Change | Why, and how to do it |
|---|---|
| Fibre, built up gradually | Wholegrains, pulses, fruit and vegetables. Adding a lot at once causes wind and bloating, which is unwelcome enough in pregnancy without it being avoidable. |
| Fluid, genuinely more of it | Requirements are higher in pregnancy, and fibre without fluid is counterproductive. |
| Walking, as much as is comfortable | Even short, frequent walks help transit. |
| Use the time after breakfast | The bowel is most active after a meal. Unhurried time then is more productive than trying when convenient. |
| A footstool | Knees above hips reduces straining — which matters more in pregnancy, because straining is what produces piles. |
Prunes and other sorbitol-containing fruits — apricots, apples, grapes, raspberries — are worth trying before anything from a pharmacy.
What is used if that is not enough
| Step | Usual choice in pregnancy |
|---|---|
| First | A bulk-forming laxative — ispaghula husk — taken with plenty of fluid |
| Next, if stools remain hard | An osmotic laxative — lactulose is long established in pregnancy, and macrogol is also used |
| If stools are soft but will not pass | A short course of a stimulant, on advice, sometimes with a glycerol suppository if the response is inadequate |
Check with your midwife, GP or pharmacist before taking anything, including products bought over the counter. The choices above are the usual ones, but what is right depends on how far along you are and on the rest of your pregnancy care. This is one of the areas where a two-minute conversation genuinely changes the answer.
What to be careful with
- Stimulant laxatives close to term — used only on advice, and generally kept to short courses
- Castor oil and herbal "cleansing" preparations — avoid entirely
- Repeated enemas — not something to self-administer in pregnancy
- Straining hard — the thing most worth avoiding, and the reason for treating constipation rather than tolerating it
- High-dose magnesium salts — not a pregnancy self-treatment
Why it matters for piles and fissures
Constipation in pregnancy is the main driver of two other very common pregnancy problems. Straining against hard stool, with pelvic veins already under more pressure and progesterone relaxing vein walls, is how haemorrhoids develop. An anal fissure — a tear that causes sharp pain on passing stool — then makes people put off going, which hardens the stool further.
Keeping stool soft is therefore not just about comfort; it is the practical prevention for both. Piles in pregnancy and after birth covers that side of it.
After the birth
The first bowel movement after delivery is something many people dread, and it is worth planning for rather than hoping about.
- Ask about a laxative before you need one, particularly after a caesarean, a tear or an instrumental delivery
- Codeine-based painkillers given after delivery cause constipation — reliably. If you are given them, a laxative alongside is reasonable to ask for
- Keep fluid up, particularly if breastfeeding
- Support the perineum with a clean pad when opening your bowels if you have stitches; it reduces the fear as much as the discomfort
- It will not undo your stitches. This is the specific worry people rarely voice
When to speak to your midwife or GP
Contact your midwife or GP if: constipation is not improving despite treatment; there is bleeding from the back passage; there is abdominal pain that is severe, persistent or comes in waves; you have not opened your bowels for several days and feel bloated and sick; or you have any leakage or soiling with a blocked feeling. Severe abdominal pain with vomiting and inability to pass wind needs same-day assessment.
Bleeding in pregnancy is usually from a haemorrhoid or fissure, but it should still be looked at rather than assumed.
Progesterone relaxes the bowel wall from early pregnancy, which slows transit and gives the bowel longer to absorb water from the stool. Later, the growing uterus adds physical pressure. Reduced activity, nausea limiting food and fluid, and iron supplements all add to it. Usually yes, with advice. A bulk-forming laxative such as ispaghula husk is the usual first choice, taken with plenty of fluid. If stools remain hard, an osmotic laxative such as lactulose or macrogol is commonly used. A short course of a stimulant is sometimes used on advice. Check with your midwife, GP or pharmacist before taking anything, including over-the-counter products. Yes, commonly, and iron is often the point at which manageable constipation becomes a problem. Do not stop the iron on your own, because anaemia in pregnancy matters. Raise it instead: a different iron salt, a lower dose, or alternate-day dosing are all options. It is worth avoiding. Straining against hard stool, with pelvic veins already under more pressure and vein walls relaxed by progesterone, is the main way haemorrhoids and anal fissures develop in pregnancy. Keeping stool soft is the practical prevention for both. No. Passing a stool will not undo perineal stitches, although the fear of it is very common. Supporting the area with a clean pad can help, and asking about a laxative before you need one is sensible, particularly if you have been given codeine-based painkillers, which reliably cause constipation.Frequently Asked Questions
Why is constipation so common in pregnancy?
Can I take laxatives while pregnant?
Do iron tablets cause constipation in pregnancy?
Is straining bad in pregnancy?
Will opening my bowels after birth damage my stitches?
References
- NHS. Constipation. nhs.uk
- National Institute for Health and Care Excellence. Clinical Knowledge Summary: Constipation. cks.nice.org.uk
- Electronic Medicines Compendium. Movicol 13.7g powder for oral solution: Summary of Product Characteristics. medicines.org.uk
- National Institute for Health and Care Excellence. Suspected cancer: recognition and referral (NG12). nice.org.uk
- National Institute for Health and Care Excellence. Quantitative faecal immunochemical testing to guide referral for colorectal cancer in primary care (DG56). nice.org.uk
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. A persistent change in bowel habit, rectal bleeding or unexplained weight loss should always be assessed rather than treated as constipation. Always consult a qualified healthcare professional for diagnosis and treatment. In a medical emergency, call 999.