Heartburn during pregnancy is caused by a combination of hormonal changes and physical pressure on your stomach as your baby grows. It affects roughly 40% of pregnant women overall, and nearly half of all women in the third trimester. The good news: it’s almost always harmless and typically disappears after delivery.
How Pregnancy Hormones Cause Heartburn
The main culprit is progesterone, a hormone that rises sharply throughout pregnancy to support the growing baby. Progesterone has a direct relaxing effect on smooth muscle throughout your body, which is useful for keeping the uterus from contracting too early. But it also relaxes a ring of muscle at the bottom of your esophagus called the lower esophageal sphincter. That muscle normally acts as a one-way valve, letting food drop into your stomach while keeping acid from splashing back up.
When progesterone loosens that valve, stomach acid can creep into the esophagus, producing the burning sensation in your chest and throat. This is why heartburn can start surprisingly early in pregnancy, even in the first trimester, well before your belly is visibly large. Progesterone levels climb steadily from the moment of conception, so some women notice reflux within the first few weeks.
Why It Gets Worse Later in Pregnancy
As your uterus grows from roughly the size of a pear to the size of a watermelon, it pushes your abdominal organs upward and into tighter quarters. By the third trimester, your stomach, liver, and intestines have all shifted to make room for the baby. That compression squeezes your stomach, increasing the pressure inside it and making it easier for acid to escape upward past an already-relaxed valve.
The numbers reflect this clearly. In one study of 400 pregnant women, heartburn prevalence jumped from about 35% in the first trimester to 31% in the second trimester and nearly 47% in the third. The combination of peak progesterone levels and maximum physical pressure explains why the final months are often the worst for reflux symptoms.
Who Gets It Worse
Women carrying twins or other multiples are especially prone to heartburn. The uterus grows larger and faster, compressing the stomach earlier and more aggressively. Progesterone levels also tend to run higher in multiple pregnancies. If you had frequent heartburn or reflux before becoming pregnant, you’re more likely to experience it during pregnancy as well, since the underlying valve may already be somewhat loose.
Other factors that increase your risk include eating large meals, lying down soon after eating, and gaining weight rapidly. These are the same triggers that cause heartburn outside of pregnancy, but the hormonal and physical changes amplify their effects.
Foods and Drinks That Make It Worse
Certain foods are well-known reflux triggers, and pregnancy makes your system more sensitive to them:
- High-fat and fried foods, which slow digestion and keep acid in the stomach longer
- Spicy foods, which can irritate the esophageal lining directly
- Chocolate, which relaxes the esophageal sphincter further
- Citrus fruit juices, which are acidic on their own
- Caffeinated drinks like coffee, tea, and cola
- Large meals, which overfill a stomach that already has less room
You don’t necessarily need to eliminate all of these. Pay attention to which ones trigger your symptoms and cut back on those specifically. Eating smaller, more frequent meals instead of three large ones is one of the most effective changes you can make.
How to Get Relief
Simple position changes can make a real difference, especially at night. Propping your head and shoulders up when you go to bed helps prevent stomach acid from traveling up the esophagus while you sleep. Sleeping on your left side also helps, both for reflux and for blood flow to the baby. Avoid eating within two to three hours of bedtime so your stomach has time to partially empty before you lie down.
During the day, stay upright after meals. Bending over or slouching increases abdominal pressure and pushes acid upward. Wearing loose-fitting clothing around your midsection can also reduce compression on an already-crowded stomach.
When lifestyle changes aren’t enough, antacids containing calcium or magnesium are considered safe during pregnancy and work quickly. These are the preferred options because high doses of aluminum-based antacids may not be ideal for fetal development. If over-the-counter antacids aren’t controlling your symptoms, stronger acid-reducing medications are available. Some are classified as likely safe in pregnancy, but it’s worth discussing specific options with your provider since the safety profiles vary.
When It Might Not Be Heartburn
Most pregnancy heartburn is exactly what it feels like: annoying but harmless. However, upper abdominal pain, particularly under the ribs on the right side, can sometimes be confused with heartburn when it’s actually a sign of preeclampsia, a serious pregnancy complication involving high blood pressure. This type of pain, called epigastric pain, can also be mistaken for gallbladder problems or indigestion.
The key differences: preeclampsia-related pain tends to be persistent and severe rather than the familiar burning sensation that comes and goes. It often appears alongside other symptoms like sudden swelling, headaches, or vision changes. If you experience sharp or unusual upper abdominal pain that doesn’t respond to antacids, especially after 20 weeks, contact your healthcare provider right away rather than assuming it’s just heartburn.