Some forms of inflammatory bowel disease are a bigger threat to pregnancy than others, suggests a large new U.S. analysis.
One of two major types of IBD, ulcerative colitis, was most strongly linked to serious pregnancy complications, researchers found in a study of nearly 400,000 women.
But all women with IBD can and should take precautions for a safe pregnancy, experts said.
"A sick mother is not good for a growing pregnancy," Dr. Shannon Clark, an obstetrician in the Division of Maternal-Fetal Medicine at the University of Texas Medical Branch at Galveston, told Reuters Health by email.
Crohn's Disease and ulcerative colitis are the main forms of IBD. Both affect the digestive tract, although the Crohn's and Colitis Foundation of America defines ulcerative colitis as a chronic disease of the large intestine, while Crohn's disease is a chronic inflammatory condition of the entire gastrointestinal tract.
The causes of ulcerative colitis and Crohn's disease remain largely unknown, and there are currently no cures for the disorders. In the U.S., approximately 200 people out of every 100,000 are affected by the conditions.
Both forms of IBD have been linked with disorders of the eyes, skin, joints and liver, the researchers point out.
And IBD in general has been tied to pregnancy complications involving inflammation and blood flow problems, write lead study author Dr. Darios Getahun, a researcher with Kaiser Permanente Southern California Medical Group in Pasadena, and his colleagues in the Journal of Perinatology.
Up to one third of all pregnant women with IBD will experience a flare-up of the condition during pregnancy, or worsening of symptoms, according to Clark, who was not involved in the new study.
Getahun's team wanted to see whether the type of IBD a woman has makes a difference in her risk for pregnancy complications such as spontaneous preterm delivery, problems with blood flow to the placenta and placental rupture.
The researchers looked at medical records of 395,781 women who delivered singleton pregnancies in all Kaiser Permanente Southern California facilities between 2000 and 2012.
In 130 out of 100,000 pregnancies, the women had IBD and those women did have higher rates of certain pregnancy complications. They were 46 percent more likely to have a child that was small for its gestational age than women without IBD, for example.
Women with IBD were also 32 percent more likely to have a spontaneous preterm delivery and nearly twice as likely to have a premature rupture of the placenta.
The early deliveries tended not to be too severe - on average, they were around 34 to 36 weeks of pregnancy (39 to 40 weeks is considered full term), the researchers note.
When the researchers further analyzed the results, they found the increased risk was significant only among women with ulcerative colitis.
For that reason, Getahun and his colleagues write, doctors may want to take into consideration the specific type of IBD a patient has when planning for treatment during pregnancy.
"A diagnosis of inflammatory bowel disease does mean that a woman who is pregnant would need to be on medication throughout the course of her pregnancy to control symptoms," Clark said.
"If the symptoms of IBD are uncontrolled, or the disease is in an ‘active' state, at the time of conception, the woman will likely continue to experience the symptoms of active disease throughout her pregnancy," Clark said.
Dr. Leah Battista, a maternal-fetal medicine specialist at Kaiser Permanente Southern California Medical Group, who was not involved in the study, advised women who have inflammatory bowel disease to make sure they're in remission at least six months before becoming pregnant.
Getting IBD into remission is harder to manage during a pregnancy, Battista said, adding that it's important to "practice safe and effective birth control while in remission."
Clark agreed, the best preventive measure is to maintain control of IBD symptoms prior to conceiving. "It is crucial that a woman remain on the medications that have put her IBD in remission," Clark said. "It may also be helpful to have pre-conceptional counseling with a maternal-fetal medicine specialist, in conjunction with the physician who has been managing her IBD, in order to properly plan for the upcoming pregnancy."