Is it true that a lot of heartburn means that the baby will have a lot of hair?
One publication confirmed that this is maybe true. There is one publication confirming that women with heartburn are somewhat more likely to have a female fetus. In this 2006 publication, the authors say that "...Most (23/28) women who reported moderate or severe heartburn gave birth to babies with average or above average amounts of hair, and conversely, most (10/12) women reporting no heartburn had babies with less than average or no hair."
Heartburn is common during pregnancy because, as the stomach is pushed higher by the growing baby and the expanding uterus, it becomes easier for acid to move backward (or "reflux") from the stomach into the lower esophagus. Acid is irritating to the esophagus and causes the discomfort we know as heartburn. Remaining upright after eating, sleeping with the head of the bed at a slight elevation, and antacid medications (many of which are considered safe during pregnancy) can be helpful. Check with your obstetrician before taking any medications during pregnancy, including over-the-counter remedies.