The first study* reviewed the risks of complications in the course of the pregnancy. In conducting the review, the authors looked at 23 different studies of pregnancy and inflammatory bowel disease. They found an increase risk for preterm birth, low birth weight, stillbirth, and birth defects.
The study — like many medical articles — reported odds ratios (OR). Odds ratios don’t tell us how likely something is — only how much more likely it is compared to a regular person. But using those odds ratios and other published data, we can work out a rough estimate of actual risks based on this paper:
- Preterm birth: the study reports an OR of 1.85, which works out to roughly 22 in 100 babies whose mothers have IBD will be born before 37 weeks, compared to 13 in 100 preterm babies for all births in the U.S.
- SGA birthweight: the study reports an OR of 1.36, which means roughly 13 in 100 babies for IBD mothers will have ‘small for gestational age birthweight’, compared to 10/100 births in the U.S.
- Stillbirth: the study reports an OR of 1.57, meaning roughly 9 in 1,000 babies for IBD mothers will be stillborn, compared to 6 in 1,000 in the U.S.
- Congenital abnormality: the study reports an OR of 1.29; roughly 5 in 100 babies for IBD mothers will be born with a birth defect, compared to 4 in 100 in the U.S.
Note that these risks are for mothers with active disease. One of the authors of the study, Dr. Aiobhlinn O’Toole, writes, “the take home message is that if disease is controlled at conception pregnancy should be uncomplicated”. (Although this study is paywalled, Dr. O’Toole graciously provided us a copy.)
- Pregnancy loss: the authors found that 5 in 100 of women without IBD lost their pregnancy, compared to 5 in 100 for women with CD and 4 in 100 of women with UC. These differences were not big enough to be statistically significant (that is, they were within the margin of error).
- Pre-eclampsia: there was a 3 in 100 chance of pre-eclampsia for women with and without IBD. However, there was a higher — but still very small — risk of severe pre-eclampsia in women with IBD, especially in women who used oral steroids (e.g. prednisone) during their pregnancy.
- Pre-term delivery: women with IBD were twice as likely as women without to have deliver pre-term — about 10 in 100 women with IBD, compared to 5 in 100 for women without. Again, steroid use posed a higher risk, and an especially high risk of premature rupture of membrane (that is, ‘water breaking’). Even women with IBD who did not take any medications during their pregnancy had a somewhat higher risk of early delivery.
- Birth outcomes: the study authors looked at Apgar score — a measure of the baby’s health at birth — and found no significant differences between mothers with IBD and mothers without. For congenital abnormalities (birth defects), the study also showed no difference overall between women with IBD and women without. However, when looking at specific types of IBD, there was a somewhat higher risk of birth defect in mothers with Crohn’s: about 10 in 100, compared to 8 in 100 for mothers without IBD.
This study is valuable because it gives us insight into how IBD affects pregnancy, but also how IBD treatments affect pregnancy. In their conclusions, the authors point out that much of the risk in the study came from women who took steroids during their pregnancy — especially for severe pre-eclampsia, premature rupture of membrane, and medical pre-term delivery. They also note that none of the women took biologic medications (Remicade, Humira), because those were not yet available in the Denmark by 2002.
The authors also point out that even for women not taking medications, there are still some risks of premature rupture and pre-term delivery, and also for birth defects in babies born to women with Crohn’s Disease. These risks are very small, but higher than for women without IBD. This means that even disease in remission may cause complications in pregnancy — but again, those risks are small in absolute terms.
These two studies help provide a clear picture of the risks IBD poses to pregnancy, but nothing here should discourage a women with the disease from considering pregnancy. Women with IBD who intend to get pregnant should — of course — talk to their physicians about their disease, the medications they take, and a plan of treatment during the pregnancy.
But the good news is that the vast majority of women with Crohn’s and UC will have normal pregnancies — 78 in 100. Even more will deliver healthy babies — 87 in 100, or more. This should be a comfort to would-be mothers wrestling with IBD.
*O’Toole, A.; O. Nwanne; & T. Tomlinson. “Inflammatory Bowel Disease Increases Risk of Adverse Pregnancy Outcomes: A Meta-Analysis”. Digestive Diseases and Sciences, June 2015.
**Boyd, H. et al. “Inflammatory Bowel Disease And Risk of Adverse Pregnancy Outcomes”. PLOS One, June 2015, DOI: 10.1371/journal.pone.0129567
Photograph “Baby Kyle” used under Creative Commons modifications & commercial license from Flickr user Julia Rosario Photography.