More than one-half of all pregnant women report symptoms of severe
heartburn, particularly during their second and third trimesters. Heartburn,
also called acid indigestion, is an irritation or burning sensation of the
esophagus caused by stomach contents that reflux (come up) from the
stomach.

Heartburn may occur during pregnancy because of changing hormone levels,
which can affect the muscles of the digestive tract and affect how different
foods are tolerated. Pregnancy hormones can cause the lower esophageal
sphincter (the muscular valve between the stomach and esophagus) to relax,
allowing stomach acids to splash back up into the esophagus. In addition, the
enlarged uterus can crowd the abdomen, pushing stomach acids upward.

How Can I Reduce Heartburn Symptoms Without Hurting My Baby?

To reduce heartburn without hurting you baby, you should try the
following:

• Eat several small meals each day instead of three large ones.


• Eat slowly.


• Avoid fried, spicy or rich foods, or any foods that seem to cause
  relaxation of the lower esophageal sphincter and increase the risk of
  heartburn.


• Drink less while eating. Drinking large amounts while eating may increase
  the risk of acid reflux and heartburn.


• Don't lie down directly after eating.


• Keep the head of your bed higher than the foot of your bed. Or place
  pillows under your shoulders to help prevent stomach acids from rising into
  your chest.


• Ask your doctor about using medications such as Tums or Maalox, which are
  generally safe to use during pregnancy. You may find that liquid heartburn
  relievers are more effective in treating heartburn as they coat the
  esophagus.


• Wear lose-fitting clothing. Tight-fitting clothes can increase the pressure
  on your stomach and abdomen.

If your heartburn persists, see your doctor. He or she may prescribe
medications that are safe to take during pregnancy. Heartburn usually
disappears following childbirth.

http://www.webmd.com/heartburn-gerd/heartburn-during-pregnancy