I'm not talking about constipation and common diarrhea here. Constipation is famous in pregnancy due to the decreased mobility of the bowels under the influence of progesterone. Common diarrhea is usually a brief self-resolving illness unrelated to pregnancy.
What I discuss here is maternal inflammatory bowel disease (IBD), the most famous of which are Crohn's Disease and Ulcerative Colitis. These are sometimes debilitating immunological diseases that cause bowel damage which can cause pain, nutritional abnormalities, and can even lead to surgery or death. Today, treatment (including steroids and the antibiotics sulfasalazine and metronidazole) has made such dire complications rare. And thankfully, getting pregnant during times of quiet for these diseases usually means things will go smoothly for the pregnancy. But there can be flare-ups of both Crohn's Disease and Ulcerative Colitis, most frequently in the first and third trimesters and then post-partum. So before attempting pregnancy, an IBD patient should consult with both her OB-GYN and her gastroenterologist.
Newly diagnosed IBD during a pregnancy is unlikely and therefore suspicious, so other causes need to be ruled out, like a weird presentation of appendicitis. And appendicitis will always be a weird presentation during pregnancy, because the location of the appendix is pushed up and away from the famous right lower spot of the abdomen. Also, ovarian complications like benign cysts or torsion (twisting upon itself) can present with abdominal pain, nausea, and diarrhea, just like IBD. But it would be quite the coincidence to have a patient's very first episode of IBD occur during her pregnancy, so an obstetrician must always consider these other things with an initial presentation of symptoms like this during pregnancy.
IBD is a chronic situation, so most pregnant women with complications of IBD come to their obstetricians with a diagnosis way in advance. The second trimester, as is true with most problemmatic situations in pregnancy, is the quietest third of the pregnancy. Statistics are not very helpful with IBD in pregnancy, because one-third will get better, one-third will remain unchanged, and one-third will get worse. A patient with IBD will discover that no one can tell her what to expect, because such even statistics provide no perspective at all on the likelihood of what she herself might experience.
As bad a disease process as IBD can be, it shouldn't forbid pregnancy in women who want children. And the treatments for IBD have little risk to the baby, meaning that flare-ups can be treated. The sometimes heart-breaking aspects of IBD are because a person has IBD, not because they have it during pregnancy. But IBD as applied to pregnancy brings up special considerations. Nutritional needs are sometimes different for IBD patients, especially those who may have had portions of bowel removed previously. Also for this reason growth of the fetus should be monitored closely with ultrasound, as dietary derangements can affect fetal growth.
Unless the disease has resulted in distortion of the anatomy—fisutlas of the rectum or obliteration of the rectum surgically, a vaginal delivery can be anticipated. But if the anatomy there is abnormal with a chance of worsening by vaginal delivery, C-section is sometimes a better idea. Each case should be individualized.
A percentage of IBD patients also have depression, and most experts feel that the depression is not just because they're bummed out they have this disease, but that it is truly a related phenomenon—a "co-disease" state. Add in the psychodynamics of worry over a high-risk pregnancy and fluctuating hormones, plus the slightly hyperthyroid affects of hCg (the pregnancy hormone), and a woman's mental health must also be respected.
In this series I've written so far, pregnancy complicated by each medical condition has its own set of special considerations, and these are the special considerations for Irritable Bowel Disease in pregnancy.