Ulcerative Colitis Flare During Pregnancy

Pregnancy does not reliably calm ulcerative colitis (UC), and for UC specifically the best prospective evidence points the other way. In a European study that followed pregnant women with IBD trimester by trimester and compared them with non-pregnant women, pregnant women with UC were about twice as likely to relapse during pregnancy, mostly in the first and second trimesters, and more likely to relapse in the six months after birth (Pedersen 2013). Women with Crohn's disease in the same study showed no such difference. If you are breastfeeding, our guide to breastfeeding with ulcerative colitis covers medicines in milk and what the 2025 consensus says.

That is not a reason for panic. It is a reason to plan for a flare rather than hope one will not come, to know which of your usual warning signs stop working in pregnancy, and to get a flare treated early when it arrives. A flare in pregnancy is linked with more preterm births and smaller babies, but most pregnancies in people with UC, including many with flares, end with a healthy baby. This guide covers what the research actually shows, where popular summaries get it wrong, how to tell a flare from ordinary pregnancy symptoms, what monitoring is realistic, and what tends to happen after delivery. If you have a pouch, pregnancy with a j pouch covers delivery and pouch function.

Does pregnancy make ulcerative colitis flare?

For UC, the best prospective data say pregnancy is linked with more relapses, not fewer. The European Crohn's and Colitis Organisation's epidemiology group enrolled pregnant women with IBD in 12 European countries between 2003 and 2006, matched each at conception with a non-pregnant woman with IBD, and collected disease course at every trimester and for six months after birth. Of the 209 pregnant women, 117 had UC. Pregnant women with UC were more likely to relapse than non-pregnant women with UC during pregnancy (relative risk 2.19, 95% CI 1.25 to 3.97) and after delivery (relative risk 6.22). For Crohn's disease the study found no statistically significant difference between pregnant and non-pregnant women (Pedersen 2013).

This matters because a lot of general advice about "IBD and pregnancy" blends the two conditions together, and the blend hides the UC signal. One specialist clinic page we read for this article tells readers that if IBD is in remission at conception, "the chance of a flare during pregnancy is similar to when you are not pregnant." For Crohn's disease, that matches the European study. For UC, the same study found the opposite, and the comparison group in that study was exactly the one the claim is about: women with UC who were not pregnant.

Two honest limits. First, 117 women with UC is not a large number, which is why the confidence intervals are wide. Second, we could read the abstract of this study but not its full text, so we cannot tell you the raw relapse percentages in each group, only the relative risks the abstract reports. What the study does settle is the direction: if you have UC, planning for a possible flare during pregnancy is sensible, not pessimistic.

The "rule of thirds" and why it does not fit UC

You will often read that pregnancy has a one-third, one-third, one-third effect on UC. A UK clinical reference site used by GPs, for example, lists the effect of pregnancy on UC as one third improving, one third worsening and one third flaring after delivery. We could not find a modern study that produced those proportions, and the page we read did not cite one for that line.

The more recent evidence does not divide that neatly:

• The European study above found pregnant women with UC relapsed more than non-pregnant women both during pregnancy and after it, which is not what "a third improve" would predict as an average (Pedersen 2013).
• A meta-analysis pooling ten studies of 1,130 pregnant women with UC found that what happened during pregnancy depended heavily on whether the colitis was active at conception, which the rule of thirds ignores entirely (Abhyankar 2013).

The rule survives because it sounds balanced and because it matches something real: pregnancy does go very differently for different people. In the threads we read for this article, one person described their first pregnancy as the best remission they had ever had, and their second, started with mild symptoms, as an awful flare that needed iron infusions (r/UlcerativeColitis). Others described flaring from 12 weeks onwards, at 9 weeks, or for the first time in years at 8 months.

Why one pregnancy can be calm and the next one hard

There is a small but intriguing study suggesting the baby's genes may play a part. Researchers genotyped 50 mother and child pairs from pregnancies in 38 women with IBD. Improvement during pregnancy was more likely when mother and baby were mismatched at two immune-system gene sites, HLA-DRB1 and HLA-DQ, with an odds ratio of 8.4. Disease activity before pregnancy was also an independent predictor (Kane 2004).

Treat this as a plausible mechanism, not a test you can take. It was 50 pregnancies, the confidence interval reported in the abstract (1.5 to 14) is very wide and sits oddly around its point estimate, and it has not become part of clinical care. But it fits a pattern that people in the UC community describe: each pregnancy carries a partly different immune situation, so a calm first pregnancy does not guarantee a calm second one, and a hard one does not doom the next.

If you conceived while flaring, or in a grey zone

Conceiving with active UC is the clearest risk factor for being active during pregnancy. In the meta-analysis of ten UC studies, 55% of women who became pregnant while their UC was active stayed active during pregnancy. The risk ratio compared with women in remission at conception was 2.0 (95% CI 1.5 to 3) (Abhyankar 2013).

What this means in practice is less dramatic than it sounds. Even in that pooled data, nearly half of women who conceived while active did not remain active through pregnancy, and between roughly two thirds and seven in ten of those who conceived in remission stayed well. Many people in the threads describe exactly the grey zone the studies struggle to classify: mild inflammation on the last scope, occasional blood that may be haemorrhoids, stable on a biologic, two years of waiting (r/UlcerativeColitis). That is a conversation to have with your IBD team before trying, because they can tell you whether "mild" means "mild but still inflamed", and whether there is room to get deeper control first. It is not a question an article can answer for you.

If you are already pregnant and were not in remission, the useful step is the same: tell your IBD team early, not at your next routine appointment. One person in a thread about flaring at 9 weeks described their gastroenterologist arranging steroids, iron, a referral to an IBD specialist and maternal-fetal medicine within a week of the conversation (r/UlcerativeColitis). Speed matters more than the specific plan.

When in pregnancy do UC flares happen?

In the European study, UC relapse during pregnancy was concentrated in the first and second trimesters. The abstract reports a relative risk of 8.80 for the first trimester and 2.84 (95% CI 1.2 to 7.45) for the second, compared with non-pregnant women with UC over the same period (Pedersen 2013).

Those numbers come with a problem we have to flag. The abstract prints the same confidence interval, 2.05 to 79.3, for two different estimates: the first-trimester relative risk of 8.80 and the postpartum relative risk of 6.22. Two different estimates sharing an identical interval to one decimal place looks like a transcription error in the abstract. We could not access the full text to check. The wide intervals reflect how few women contributed to each time slice. So read the first-trimester finding as "early pregnancy appears to be a higher-risk window for UC", not as "an eightfold risk".

That early-pregnancy concentration lines up with what people describe. In the threads we read, people reported flares at 9 weeks, from 12 weeks onward, and from the first trimester after unexpectedly stopping a medicine. Late flares happen too: one person in their eighth month described their first bleeding in years after missing doses while wrapping up work before maternity leave (r/UlcerativeColitis).

The third trimester matters for a different reason. Activity in the third trimester was the strongest predictor of a postpartum flare in a US study (more on that below), so a flare late in pregnancy is not just a problem for the remaining weeks.

Is a UC flare during pregnancy dangerous for the baby?

Active disease is linked with higher risks of preterm birth, low birth weight and miscarriage, but the absolute picture is better than the relative numbers suggest. A 2021 meta-analysis of 28 studies compared women with active and inactive IBD at conception or during pregnancy (Kim 2021):

In the UC subgroup, active disease was linked with higher risks of low birth weight, preterm birth and miscarriage. The stillbirth interval only just clears 1, so that estimate is the least secure in the table.

Odds ratios describe how much the odds change, not the chance that something will happen to you. Two other studies help put absolute numbers on it.

• Sweden. A national register study of 470,110 births included 1,833 births to women with UC. UC was linked with a higher risk of preterm birth overall (adjusted odds ratio 1.78), and risks were more pronounced in women whose disease flared during pregnancy. "Flaring" in this study was defined from records of drug use, surgery and hospital admissions, not from symptoms or tests (Bröms 2014).
• Denmark, moderate to severe disease. A nationwide cohort of 219 pregnancies in women treated with anti-TNF drugs found 66% had disease activity at some point in pregnancy. Among women with UC and disease activity, 29.3% gave birth preterm and 19.5% had a low birth weight baby (Kammerlander 2017). That is a high rate, and the authors say so. It also means roughly seven in ten of those babies were not preterm, in a group selected for severe disease.

The same Danish study is a useful lesson in reading results. Its overall adjusted odds ratios for disease activity were 2.05 for low birth weight (95% CI 0.37 to 11.35) and 2.64 for preterm birth (95% CI 0.85 to 8.17). Both intervals include 1, so on their own they do not show a clear effect. Only moderate to severe activity reached a clear increase in preterm birth (odds ratio 3.60, 95% CI 1.14 to 11.36). The signal sits with the more severe flares.

Inflammation you cannot feel may matter too

A 2025 study suggests inflammation seen on ultrasound predicts outcomes even when symptoms and blood tests look reassuring. Researchers at three specialist IBD pregnancy services followed 377 pregnant people with IBD from 2017 to 2023, with clinical scores and faecal calprotectin each trimester; 234 had an intestinal ultrasound. A maximum bowel wall thickness over 6 mm in the second trimester was linked with about four times the risk of prematurity (relative risk 4.01, 95% CI 1.26 to 12.72) and about twice the risk of a low birth weight delivery. Agreement between clinical scores and ultrasound or calprotectin was weak, particularly in Crohn's disease (Prentice 2025). The study was part-funded by Ferring Pharmaceuticals alongside university, charity and government sources.

One line in that abstract does not add up: the gestational diabetes result is printed as a relative risk of 1.08 with a 95% CI of 1.088 to 1.089, a point estimate that sits outside its own interval. It is almost certainly a typo, and it does not affect the prematurity finding, but it is a reminder to read the numbers rather than the headline.

Why this matters to you: if your symptoms are mild but your calprotectin is high, the mild symptoms are not the whole story. We cover how to sort that out in the monitoring section below.

Is it a flare or just pregnancy?

Several of the most common pregnancy symptoms overlap with UC, and none of them can be sorted reliably by feel alone. That is why new or changing symptoms in pregnancy usually need a test rather than a guess. This table is a way of organising what to report, not a way to rule out a flare.

The haemorrhoid numbers are worth knowing. In a Lithuanian study that examined 280 pregnant women four times through pregnancy and after birth, 41% developed haemorrhoids, and of the women who developed perianal disease, 61% did so in the third trimester and 34% after delivery (Poskus 2014). Constipation was one of the strongest risk factors. So late-pregnancy bleeding has a common innocent explanation. But people with UC sometimes reassure themselves with exactly that explanation for weeks, and one thread we read described months of bleeding in pregnancy before anyone took it seriously and diagnosed UC at seven months (r/UlcerativeColitis). If the bleeding is new, changing or comes with looser stools, report it rather than settling on haemorrhoids yourself. Our guide on how much blood in stool is normal with ulcerative colitis covers what bleeding patterns tend to mean.

Why your usual flare signals become unreliable in pregnancy

Pregnancy changes the very numbers that normally tell you and your team how active your colitis is. This is one of the least discussed parts of the topic and one of the most practical.

Symptom scores drift away from inflammation. In a study of 46 pregnant women with IBD and 21 pregnant women without it, faecal calprotectin tracked the doctor's overall assessment of disease activity strongly at every time point. The standard symptom indices (the Simple Clinical Colitis Activity Index for UC and the Harvey-Bradshaw Index for Crohn's) correlated with calprotectin before and after pregnancy, but not during it (Julsgaard 2017). Pregnancy adds its own bowel changes, tiredness and discomfort, so a score built for non-pregnant adults picks up noise.

CRP, albumin and haemoglobin stop tracking disease activity. A systematic review of 13 studies found no consistent correlation between CRP and active IBD in pregnancy, and none for albumin or haemoglobin either; only faecal calprotectin correlated with activity in every period of pregnancy (Tandon 2019). A Danish study of women with moderate to severe IBD likewise found no clinically significant differences in CRP, albumin or haemoglobin between active and inactive disease during pregnancy (Kammerlander 2018). Normal pregnancy dilutes the blood, which lowers haemoglobin and albumin regardless of the colon (Soma-Pillay 2016).

The severe-flare criteria lean on two numbers pregnancy moves. The criteria most hospitals use to recognise acute severe colitis combine a bloody stool count with signs of systemic illness, including a resting pulse over 90 and a haemoglobin below 10.5 g/dL. Our guide on when to go to the hospital for a UC flare walks through them. In pregnancy, resting heart rate normally rises by 10 to 20 beats a minute and haemoglobin normally falls (Soma-Pillay 2016). That cuts both ways: a pulse of 92 may be ordinary pregnancy physiology, and a pulse of 105 should not be waved off as "just pregnancy" when you are also passing frequent bloody stools. We did not find a validated pregnancy-adjusted version of these criteria in our searching, so the safe reading is that the stool count, fever and how unwell you feel carry more weight than usual, and that you should not talk yourself out of calling.

What monitoring should look like during pregnancy

Faecal calprotectin is the workhorse, intestinal ultrasound is increasingly used, and endoscopy is kept for when the answer will change the plan.

Faecal calprotectin

Pregnancy itself does not raise faecal calprotectin, which is what makes it so useful. In the study above, pregnant women without IBD had a median calprotectin of 0 μg/g (range 0 to 84), and a cut-off of 250 μg/g separated active from inactive disease, as judged by the doctor, at all five time points before, during and after pregnancy (Julsgaard 2017). In the larger Danish cohort, typical values were 80 to 120 mg/kg in clinically inactive disease, 259 to 349 in mild activity and 778 to 1,277 in moderate to severe activity. At a cut-off of 200, sensitivity ran from about 70% to 80% and specificity from about 67% to 73% across the periods of pregnancy (Kammerlander 2018). (μg/g and mg/kg are the same unit.)

Those accuracy figures are decent rather than perfect, so a single result near a cut-off is a reason to repeat or combine tests, not a verdict. Our guide to what calprotectin levels mean for ulcerative colitis covers assay differences and day-to-day variation, and all of that still applies in pregnancy.

A practical snag from the threads: one person flaring at 24 weeks explained that their team wanted a stool sample before adjusting treatment, but they were passing too little at a time to fill the pot (r/UlcerativeColitis). If that happens to you, tell the clinic rather than quietly failing to deliver one. Labs can usually advise on how little they can work with, and the clinical picture can carry the decision when a sample is not possible.

Intestinal ultrasound

Bowel ultrasound needs no preparation, no sedation and no radiation, and it works well in early pregnancy. A Dutch study followed 38 pregnant patients (16 with UC) with ultrasound each trimester. Against a reference of calprotectin plus clinical activity, ultrasound distinguished active from quiet disease with 84% sensitivity and 98% specificity. The catch is that the growing uterus gets in the way: the sigmoid colon, where UC often lives, could be seen in 95.6% of first-trimester scans but only 69.5% in the third trimester (De Voogd 2022). If your team offers ultrasound, early pregnancy is when it can see the most.

Availability varies widely. Bowel ultrasound depends on a trained operator, and many units do not have one. If yours does not, calprotectin and clinical review remain the standard.

Sigmoidoscopy and colonoscopy

A flexible sigmoidoscopy, which looks at the rectum and lower colon, can be done in pregnancy when it is needed. The best-known safety study is small and old: 26 sigmoidoscopies in 24 pregnant women across four US university hospitals over seven years. No endoscopic complications occurred, the procedure found a cause in 9 of 11 women with rectal bleeding, and 18 women delivered healthy infants, 16 at full term. One miscarriage nine weeks after the procedure, in a woman with diabetes and high blood pressure, was judged unrelated, and four pregnancies were ended by choice (Cappell 1995). Canadian consensus guidance states that endoscopy or urgent surgery should not be delayed during pregnancy if indicated (Nguyen 2016).

The honest summary is that sigmoidoscopy is considered acceptable when the result will change treatment, and that the safety data are reassuring but thin. The study above was of sigmoidoscopy only, so it tells you nothing about a full colonoscopy, which is a longer procedure and a separate decision. For a new flare in someone with known UC, many teams start with calprotectin and stool tests for infection and reserve a scope for when the picture is unclear or not responding.

The medication question, without the medication advice

We are not going to tell you which drug to take or stop. What we can show you is what the research says about stopping. The questions that dominate the threads are about prednisone and cleft palate, whether a biologic is safe, and whether a rectal product whose box says "not for use in pregnancy" is really fine. Those are drug-specific decisions for your IBD team, and the guidance genuinely differs between medicines. But one pattern runs through almost every study.

Stopping treatment out of fear is common, and it is linked with flares.

• In a survey of 204 women with IBD, 101 of whom had been pregnant, 47 (46.5%) reported stopping a prescribed IBD medicine while pregnant or trying to conceive, and 20 of those 47 did so without a doctor's advice. When offered the choice in a structured exercise, participants consistently preferred not to stay on the most effective therapy (Gallinger 2016).
• A French national database study of 11,275 pregnancies found that interrupting anti-TNF treatment before week 24 increased the risk of relapse. The same study found anti-TNF use was linked with more maternal complications and infections in the mother, and no increased infection risk in babies up to one year (Luu 2018). Most of the exposed pregnancies were in Crohn's disease (only 144 were UC), so it is not UC-specific evidence. We include both halves because both are real: treatment decisions in pregnancy are trade-offs, not free choices.
• In a US study of postpartum flares, cutting back therapy during pregnancy roughly tripled the odds of flaring after birth (odds ratio 3.00, 95% CI 1.03 to 8.68) (Yu 2020).

Guidelines have moved firmly towards keeping the mother's disease controlled. Canadian consensus guidance concluded that women on 5-ASA, thiopurine or anti-TNF monotherapy for maintenance should, in general, continue it throughout pregnancy (Nguyen 2016). A global consensus published in several journals in 2025 and 2026, written by 39 IBD and content experts and 7 patient advocates from six continents, was built on the guiding principle that "maternal health best supports infant health" (Mahadevan 2026). We could read only its abstract, not its 69 recommendations, so we are not quoting anything from inside it. Its published competing-interest statement lists extensive consulting and advisory relationships with drug manufacturers among its authors, including the lead author. That does not make it wrong, but you should know it.

What the steroid data actually show

Steroids in pregnancy are linked with worse outcomes in registry data, but that data cannot fully separate the drug from the flare that required it. In the US PIANO registry of 1,490 mothers with IBD, corticosteroid use was associated with preterm birth (adjusted odds ratio 1.79), low birth weight (1.76) and neonatal intensive care admission (1.54). Steroid use in the second or third trimester was linked with more serious infections in babies at 9 and 12 months (4% versus 2% and 5% versus 2%). Five babies with steroid exposure were born with orofacial clefts compared with one without, but the abstract does not give the group sizes, so those counts cannot be turned into rates (Odufalu 2022).

The authors' own conclusion is not "avoid steroids". It is that disease should be controlled before and during pregnancy with steroid-sparing therapy, which is a different message. People are usually given steroids because they are flaring, and flaring is itself linked with the same outcomes. The abstract does not let us see how fully the analysis separated the two. The registry was funded by a Crohn's & Colitis Foundation award and a family fund; two authors disclose consulting for drug manufacturers. The Canadian consensus lists systemic corticosteroids among the options for a flare in pregnancy (Nguyen 2016). If steroids are offered to you, the useful question is not "are they safe" but "what is the plan to get me off them, and what comes next if they do not work".

Blood clots: the flare risk nobody mentions

Pregnancy, the weeks after birth, and an IBD flare each raise the risk of blood clots, and they add up. In a Danish nationwide study of almost two million deliveries between 1980 and 2013, women with IBD had a venous thromboembolism rate in pregnancy of 4.20 per 1,000 person-years against 2.41 in women without IBD. An IBD flare during pregnancy was linked with a relative risk of 2.64. After birth, the rate in women with IBD was 7.03 per 1,000 person-years against 2.88 (Hansen 2017). A meta-analysis of five studies found a similar picture, with UC carrying a slightly higher relative risk than Crohn's (2.24 during pregnancy and 2.85 after it) and the increase driven mainly by deep vein thrombosis (Kim 2019).

In absolute terms, clots remain uncommon. But they are one of the reasons a flare that lands you in hospital in pregnancy, or soon after birth, is taken seriously, and one of the reasons to ask whether clot prevention has been considered if you are admitted. Know the warning signs listed at the end of this article.

After delivery: the second risk window

The year after birth is a high-risk period for UC flares, and how you finish pregnancy shapes it. Three studies give different-looking numbers that make sense once you see what each measured:

So "about a third" and "about one in ten" are both real figures from different hospitals, different time windows and different definitions of a flare. The consistent message is in the predictors: flaring late in pregnancy and stepping treatment down are the factors linked with flaring after it. The US study was funded by the National Institutes of Health and the Crohn's & Colitis Foundation.

Two common postpartum worries the data do not support:

• Pain relief after birth. Some obstetricians avoid anti-inflammatory painkillers after delivery in women with IBD. In the single-centre study above, flares within nine months happened in 9% of women given NSAIDs in hospital after birth and 14% of those not given them, and the adjusted analysis found no link (adjusted odds ratio 0.6, 95% CI 0.2 to 1.7) (Rabinowitz 2026). It is one retrospective study of short in-hospital use, and longer use outside hospital is a separate question. Ask your team what they would prefer for you.
• Breastfeeding. In a study of 122 women, breastfeeding at first looked linked with postpartum flares, but the link disappeared once the authors accounted for women who had stopped their IBD medicines in order to breastfeed. For UC on its own, there was no association at all (odds ratio 0.89) (Kane 2005). Several women in that study said they did not breastfeed because a doctor advised against it or because they feared their medicines. That is a question to settle with your team before the birth, not something to resolve by stopping treatment.

Many people in the threads describe their worst flare in the months after a baby, sometimes after a calm pregnancy (r/UlcerativeColitis). Broken sleep, the end of routine antenatal contact and, often, a gap in IBD follow-up all happen at once. Put a postpartum IBD appointment in the diary before you deliver.

What to track if you have UC and are pregnant

The aim is to give your team a clear before-and-after picture with as little effort as possible, because effort is in short supply. Pregnancy multiplies appointments and changes your body week by week, so a simple daily record does more work than usual. If you already keep an IBD symptom diary, keep its fields and add the pregnancy ones below.

Daily, in seconds:

1. Number of bowel movements, including night-time ones.
2. Whether there was blood, and roughly how much, using the same words every day.
3. Urgency, on a simple scale.
4. Stool form on the Bristol scale.
5. One line of anything unusual: vomiting, new pain, a missed dose.

Weekly or as it happens:

• Resting pulse at the same time of day, so a rise stands out from your pregnancy baseline.
• Any change in medicines, including doses missed. One person in the threads traced a late-pregnancy flare to a run of missed doses, and recording them is not about blame; it helps your team decide whether the treatment failed or simply was not taken.
• Calprotectin results with the date, and the lab or test brand.
• Iron tablets started or changed, since they can cause constipation and darker stools (Bradley 2007).

A worked example. Say you are 14 weeks pregnant, your normal is two formed stools a day without blood, and your last calprotectin before pregnancy was 60. Over ten days your log shows three, then four, then five stools a day, blood on most of them, urgency rising, and one night-time trip. Your pulse has gone from a pregnancy baseline of about 84 to 96. Nothing in that record diagnoses anything, but it turns "I think I might be flaring" into a specific report: a change starting on a named date, bleeding on seven of ten days, a new night-time stool, and a pulse ten beats above your pregnancy normal. That is the kind of message that gets a calprotectin ordered the same week rather than at your next scheduled visit. Our guide on how to track symptoms during a flare covers logging when things are moving fast.

Clairop is built for exactly this kind of quick logging: one tap for a bowel movement on the Bristol scale, with urgency, blood, mucus and night waking as optional detail, and a one-page summary to take to appointments. It does not diagnose a flare or tell you what to do about one; it makes the record you bring to your team clearer.

Who should be looking after you

The usual recommendation is shared care between an obstetric team and a gastroenterologist with IBD experience, started before conception where possible. Canadian consensus guidance names preconception counselling and access to specialist care as paramount (Nguyen 2016). In the US, many people with active IBD are also referred to a maternal-fetal medicine specialist, an obstetrician with extra training in complicated pregnancies; at least two people in the threads we read described being referred to one once they started flaring.

Access is uneven, and the threads show it. One person serving in the military described being unable to get timely specialist review and feeling pressured by employment rules around biologics (r/UlcerativeColitis). If your care feels stuck, it is reasonable to ask in writing for an IBD specialist opinion, to ask your obstetric team to contact your gastroenterologist directly, and to name the specific change you are worried about. Our list of questions to ask a gastroenterologist about colitis includes a section on pregnancy that is worth reading before your first pregnancy appointment.

Delivery. For most people with UC, how the baby is delivered is an obstetric decision rather than a UC one; the Canadian consensus says caesarean decisions should rest on obstetric grounds, with active perianal Crohn's disease as the main IBD exception (Nguyen 2016). People who have had a j pouch are a different situation with their own considerations; our article on what to know before j pouch surgery covers the fertility side of that decision.

If the pregnancy was unplanned and you are flaring

This happens, it is not a personal failing, and it is a reason to call your IBD team early rather than late. One thread we read for this topic was from someone who discovered they were pregnant during a long flare, felt ashamed, and was frightened to tell their gastroenterologist (r/UlcerativeColitis). The replies were overwhelmingly kind, and almost all said the same thing: your doctors have had this conversation many times.

Whatever you decide about the pregnancy is your decision, and it is outside the scope of this article. What is within it: your IBD team needs to know quickly, because some medicines are handled differently in pregnancy, and because getting the flare under control matters for your health whatever happens next. If you are struggling emotionally, tell your GP, obstetric team or IBD nurse. If you are in crisis, in the US you can call or text 988; in the UK and Ireland, Samaritans are on 116 123; elsewhere, findahelpline.com lists local services; or contact your local emergency services.

Myths about UC flares in pregnancy

"Pregnancy puts colitis into remission." Sometimes it does, and many people describe exactly that. On average, for UC, the prospective evidence points to more relapses in pregnancy rather than fewer (Pedersen 2013).

"A third get better, a third get worse, a third flare after." A neat rule without a modern source that matches it, and it ignores the biggest predictor, which is disease activity at conception (Abhyankar 2013).

"If you conceive in remission you are no more likely to flare than if you were not pregnant." True for Crohn's disease in the European study, not for UC (Pedersen 2013).

"The medicine is the risk; the flare is just uncomfortable." Active disease is itself linked with preterm birth, low birth weight and miscarriage (Kim 2021). Medicines do carry their own trade-offs, which is why decisions should be drug-specific and made with your team, not by stopping everything.

"You can't have a scope while pregnant." Sigmoidoscopy can be done when it will change management, and guidance says endoscopy should not be delayed if indicated (Nguyen 2016).

"Calprotectin doesn't work in pregnancy." It is the one routine marker that pregnancy itself does not push up (Julsgaard 2017).

"Breastfeeding will make you flare." The apparent link in the main study disappeared once medicine stopping was accounted for, and there was no link at all for UC (Kane 2005).

"Bleeding late in pregnancy is always haemorrhoids." Haemorrhoids are very common in the third trimester (Poskus 2014), but they do not cause looser, more frequent stools with urgency. New bleeding needs reporting either way.

When to see a doctor promptly

Contact your IBD team or maternity unit promptly, and the same day if things are getting worse quickly, if you have:

• More bloody stools than your usual pattern, or blood that is new, heavier or mixed into looser stools. See a doctor promptly.
• Six or more bloody stools a day, especially with fever, a fast pulse, dizziness or feeling faint. This needs same-day assessment.
• Severe or constant abdominal pain, a swollen or tender abdomen, or pain that is different from anything you have had in pregnancy so far.
• Vomiting so that you cannot keep fluids down, or signs of dehydration such as very dark urine or passing very little.
• Fever, particularly with diarrhoea.
• Night-time bowel movements that are new for you.
• Unexplained weight loss, or failing to gain weight as expected.
• Leg swelling, chest pain or sudden breathlessness, which need emergency care because of the clot risk.
• Reduced baby movements later in pregnancy, which needs your maternity unit straight away whatever is happening with your colitis.

Do not wait for a routine appointment because you are worried about "bothering" anyone. If you are not sure whether something counts as a flare, our guide on how to know if your ulcerative colitis is flaring covers the general signs, with the caveat from this article that symptom scores are less reliable while you are pregnant.

The honest bottom line

Ulcerative colitis is more likely to flare during pregnancy than outside it, mainly in the first half of pregnancy and in the months after birth. The strongest thing within anyone's control is the state of the colitis going in, and a common, avoidable trigger is stopping or cutting back treatment out of understandable fear. Active disease is linked with real increases in preterm birth, low birth weight and miscarriage, but the absolute picture is better than the odds ratios suggest, and most pregnancies with UC end well.

Two practical points set UC pregnancy apart from everyday UC care. Your usual yardsticks, symptom scores, CRP, haemoglobin and pulse, become less reliable, so faecal calprotectin and clinical review carry more weight. And the plan should extend past delivery, because the year after birth is a second risk window. Tell your team early, keep a simple record, and treat a flare in pregnancy as something to deal with promptly rather than something to wait out.