Heartburn, a burning sensation in the chest or throat, is a common symptom of acid reflux. Acid reflux occurs when stomach contents, including digestive acids, flow backward into the esophagus, the tube connecting the mouth to the stomach. While this can happen to anyone, it is particularly prevalent during pregnancy, affecting a significant number of pregnant individuals. Its incidence ranges widely, with reports indicating that between 17% and 80% of pregnant women experience it.
Hormonal Influence on Digestion
The significant increase in hormones during pregnancy plays a substantial role in acid reflux. Progesterone, a hormone that rises dramatically, causes smooth muscles throughout the body to relax, including the lower esophageal sphincter (LES). The LES is a ring-like muscle at the junction of the esophagus and stomach that normally closes tightly to prevent stomach contents from re-entering the esophagus. When progesterone causes this sphincter to relax, it becomes less effective, allowing stomach acid to escape back into the esophagus more easily and leading to heartburn. Other hormones, such as estrogen, can also contribute to this decreased LES pressure.
Physical Pressure from a Growing Uterus
Beyond hormonal changes, the physical growth of the uterus also contributes significantly to acid reflux during pregnancy. As pregnancy progresses, the uterus expands considerably within the abdominal cavity, placing increasing physical pressure on surrounding organs, including the stomach. This growing uterus compresses the stomach, reducing the space it occupies. This increased intra-abdominal pressure can physically force stomach contents upwards through the lower esophageal sphincter. This mechanical pressure can cause reflux even if the LES functions somewhat normally, and it exacerbates hormonally induced sphincter relaxation. This factor becomes increasingly prominent as pregnancy advances.
How Reflux Changes Throughout Pregnancy
The causes of reflux evolve across pregnancy trimesters, influencing when symptoms appear and how they progress. In early pregnancy, hormonal effects, primarily progesterone’s relaxing action on the lower esophageal sphincter, are often the main culprits, with symptoms beginning before significant physical growth of the uterus occurs. As pregnancy moves into the second and, particularly, the third trimesters, the physical pressure from the expanding uterus becomes a more dominant factor. The increasing size of the uterus places greater mechanical stress on the stomach, leading to more frequent and severe reflux symptoms as pregnancy advances, with the highest prevalence often observed in the third trimester.