Summarize:

One of the best defenses for preventing or alleviating constipation during pregnancy is ensuring you're eating a high fiber diet.  Women should aim for at least 25 g of fiber every day.  Track your fiber intake with a food journal or app to see how close you are to that goal. Fiber helps prevent constipation in two ways.  It helps make your stool softer which can make it easier to go in addition to increasing the speed of your GI system.  The best high fiber foods include:  vegetables, fruits, whole grains, beans, lentils, and starchy vegetables. If you're not currently eating a very high fiber diet, suddenly increasing your fiber intake can cause stomach aches or other gastrointestinal issues.  Slowly increase your fiber intake by a few grams over the course of several days. Many people know the importance of drinking adequate fluid and constipation prevention.  This is also especially important during pregnancy.  When you're dehydrated, your body withdraws fluid from your colon, making your stools harder and more difficult to pass.  This is a common reason for constipation.  When you're pregnant you'll need more fluids each day to help support your growing baby.  Most professionals recommend going for 12-13 glasses of water daily.  Each glass should be 8 oz.  If plain water isn't your thing, try some of these flavorful substitutes:  flavored sparkling water, decaf coffee and tea, flavored plain waters, and even low-fat milk (contains about 7 oz of water per 8 oz glass). Like fluids and fiber, regular physical activity is essential for preventing constipation.  Exercise, especially cardiovascular exercise, help get the insides of your body get moving.  This is a great an easy way to help keep things moving and prevent constipation. Aim for about 150 minutes of low to moderate intensity activity each week.  Although it's generally considered safe to continue most exercises you were doing prior to your pregnancy, you may need to modify them based on your doctor's recommendation and your level of comfort.  If you weren't very active prior to your pregnancy, that doesn't mean you can't start adding in some activity.  Start slow and with low intensity activities.  Take your time as you build up strength. Avoid any aerobic exercises that are jarring, have a lot of bouncing or have a risk of abdominal injury. Try the following exercises:  walking, slow jogging as you're comfortable, swimming, doing the elliptical machine  or using stationary bike.  What's easy or comfortable may change as your belly grows. Another common cause of constipation is iron.  Many prenatal vitamins do contain iron which may be causing your constipation.  Iron can make stools hard and difficult to pass.  If you're taking a prenatal vitamin with iron or taking an extra iron supplement, this may set you up for constipation.  Talk with your doctor about decreasing the amount of iron from a supplemental source. Even when you're pregnant, a well-planned and nutritious diet can provide you with adequate amounts of iron during your pregnancy.
Eat a high fiber diet. Drink an adequate amount of fluids. Include regular physical activity. Decrease your iron supplementation.