Digestive problems and constipation are common pregnancy complaints. This is because the colon expands and works more slowly due to the pregnancy hormone progesterone. Taking iron supplements during pregnancy may also cause constipation. Eating a high-fiber diet that includes lots of vegetables and whole wheat can help but remember to drink lots of water too. Exercise in the form of walking, water aerobics, yoga or dance can also help your digestive tract to work better.
Source: - Lärobok för barnmorskor. Faxelid, E. Course literature 2001. - Myles Textbook for Midwives. Fraser, D. och Cooper, M. Churchill Livingstone 2003.