This common pregnancy-related ailment is caused by leaking of stomach acid into an unprotected esophagus, causing a chemical burn known as heartburn.
The best relief is obtained by sucking on an antacid tablet until the pain goes away (one or two tablets).
Chewing and swallowing the tablets will also be effective but usually requires more tablets. If antacids are not available, eating or drinking anything will give some relief as it will partially buffer the acid in the esophagus and rinse it back down into the stomach.
Milk is good for this purpose because it is pH neutral and has significant buffering capability. Even small sips of water are better than nothing at providing relief.
H2 blockers, such as famatodine, cimetidine, nizatidine, or proton pump inhibitors, such as omeprazole or esomeprazole can also be used safely during pregnancy.