Heartburn starts in the first trimester, for many women, beginning around month two, and is a pregnancy symptom that lasts throughout the nine months.

When a woman becomes pregnant, the levels of progesterone in her body rise and remain elevated for the duration.  These increased levels of progesterone result in the relaxing of the stomach valve leading back to the esophagus, allowing an increased amount of stomach acid to enter the throat and thus causing that burning sensation we all associate with acid reflux.

These additional hormones due to pregnancy also cause a woman’s digestion to slow to allow her body – and the baby’s – to absorb more nutrients.  This can also result in food lingering in the stomach longer than normal, causing increased stomach agitation and heartburn, a symptom that is only exacerbated by the growing womb crowding the abdomen.

If you are experiencing the symptoms of heartburn unexpectedly and more frequently, try minimizing consumption of spicy and acidic foods and beverages, avoid caffeine and alcohol as much as possible, and opt for dairy products high in calcium or probiotics to help alleviate discomfort.

Sources - https://www.baptisthealth.com/blog/mother-and-baby-care/early-pregnancy-signs-heartburn-and-indigestion#:~:text=Yes.,consuming%20common%20foods%20and%20drinks.