You expected the swollen ankles, the morning sickness, and the burgeoning breasts. But this burning indigestion? Where’d that come from?

As the name implies, heartburn (also called gastroesophageal reflux and acid indigestion) feels like a fiery churning that starts behind your breastbone and travels up your esophagus, a tube connecting your throat to your stomach. These acids can even make it all the way up your throat.

In addition to feeling a burning sensation — which can last several minutes to several hours — you may also:

  • feel bloated
  • belch a lot
  • have a sour taste in your mouth
  • have a sore throat
  • cough frequently

While the burrito you ate for dinner probably didn’t help matters (spicy foods can make heartburn worse), the burning feeling you have has more to do with hormones than jalapenos.

If you feel like you have a three-alarm fire dancing in your chest, you’re not alone. According to one study, up to 45 percent of moms-to-be experience heartburn. And if you had heartburn before pregnancy, you’re even more likely to have it during.

Heartburn can fire up, so to speak, at any point in pregnancy, but it’s most common during the second and third trimesters. Experts aren’t exactly sure what causes the smoldering, but they suspect it’s a three-pronged problem.

Hormones

Progesterone, also called the “pregnancy hormone” because it nurtures your womb and the baby inside it, is the leading culprit behind pregnancy-related heartburn.

Progesterone acts as a muscle relaxer. In the case of heartburn, the hormone can loosen the tight muscle (called the lower esophageal valve) that closes your stomach off from your esophagus.

When you eat or drink, the muscle normally opens to let contents into the stomach before shutting tightly. But the surging progesterone levels that occur during pregnancy can make that muscle slack, allowing stomach acid to backflow up your esophagus and even into your throat.

Growing baby

As your uterus expands with your growing baby, it competes for space with some of your other organs. Like a tube of toothpaste being squeezed, your growing uterus places pressure on your stomach, making it more likely stomach acids will spill out ― especially if your stomach is full.

The more your uterus grows, the more likely your stomach will get squeezed. This may help explain why heartburn is more common as you progress through pregnancy.

Slowed digestion

Thanks to progesterone, stomach contents stick around longer than normal. As digestion slows and the stomach remains fuller longer, the chances of heartburn increase.

Heartburn can be uncomfortable, but here’s how to fire back:

1. Watch what you eat

Not surprisingly, acidic and spicy foods create more stomach acid than bland ones (till we meet again, Taco Tuesday!). Avoid citrus, tomatoes, onions, garlic, caffeine, chocolate, sodas, and other acidic foods. Also steer clear of fried or fatty foods, which slow digestion.

2. Eat frequent small meals instead of three a day

This helps to avoid overwhelming the stomach and allows it to empty quicker.

3. Sit up straight when you eat

Your mom was actually right about this — and well, a lot of other things, too. Gravity will help your food stay put.

4. Don’t eat within three hours of going to bed

Giving digestion a head start before you lie down — which slows the emptying of your stomach — for the night will help control your heartburn.

5. Don’t smoke

There are a lot of reasons why you shouldn’t smoke during pregnancy, and heartburn is just one of them. Chemicals in cigarettes cause the valve that keeps stomach contents down to relax. This allows acids and undigested foods to splash upward and take their fiery aim.

6. Elevate your head 6 to 9 inches when you sleep

The easiest way to achieve this is by placing pillows under your shoulders, raising the head of your bed with blocks placed underneath the bed’s legs, or buying a special wedge pillow to place between the mattress and box spring. Sleeping propped up is another way to have gravity work for you.

7. Wear loose-fitting clothing

Step away from the Spanx and any other garment that creates pressure around your midsection. Rock your bump, and the stretchy, comfy pants, too!

8. Drink after meals, not with them

Drink liquids along with your food and you could be creating an overfull, sloshy stomach environment primed for heartburn.

9. Give acupuncture a try

In a 2015 study, pregnant women who received acupuncture versus those who didn’t showed no difference in their symptoms — but the women who had acupuncture did report improvement in their ability to sleep and eat.

10. Don’t drink alcohol

Besides the fact that exposure to alcohol can cause all kinds of problems for your developing baby ― everything from low birth weight to learning disabilities ― alcohol can also relax the valve that keeps stomach contents in the stomach.

11. Talk to your doctor about heartburn medications

This includes over-the-counter (OTC) ones — some are safe to take during pregnancy.

Antacids help neutralize the acid in your stomach and quell that burning sensation. The University of Wisconsin School of Medicine and Public Health says OTC antacids containing calcium carbonate (like Tums) are safe to use.

If you haven’t been able to quiet your heartburn with lifestyle changes, your doctor may suggest heartburn drugs like Tagamet, Prilosec, and Zantac, which are generally considered safe during pregnancy. While these drugs are available OTC, you might receive a prescription for a stronger dose if your doctor thinks it’s warranted.

When you’re pregnant, you have to think about the safety of everything you put into and on your body. Some heartburn medications that might be OK for your nonpregnant sister ― but not for you ― include:

  • Antacids containing sodium bicarbonate, which can increase swelling.
  • Antacids containing aspirin, which can be toxic to your baby. Aspirin use during pregnancy has been associated with pregnancy loss, heart defects, and bleeding on the brain in premature infants. (In some cases, your doctor may have you on aspirin as a treatment or preventative for other pregnancy complications, like preeclampsia.)
  • Antacids containing magnesium trisilicate, which haven’t been proven safe to use in pregnancy.

While pregnancy heartburn is common and uncomfortable, the sizzle should subside once you give birth and hormone levels return to normal.

You may not be able to prevent heartburn, especially if you’re prone to it even when you’re not pregnant, but you can help put out the flames with some simple lifestyle changes, such as eating small meals, avoiding spicy or fatty foods, and sleeping with your head and shoulders elevated.

If these measures don’t bring enough relief, talk to your doctor about medications that are safe to use during pregnancy.