Most heart problems you’re born with happen by chance. No one knows what causes them. A heart valve problem may come on after an infection or other health condition. Rheumatic fever caused by strep throat is a common source of infection that affects heart valves.
Even if your heart disease doesn’t cause symptoms or hasn’t affected your life, it can cause issues during pregnancy. This is because of changes in your body that happen when you’re pregnant. Some women don't know they have pre-existing heart disease until the stresses of pregnancy reveal the problem.
Starting in your first trimester, your blood volume rises by about half. The extra fluid makes your heart work harder. Your heart responds by increasing its cardiac output. This is the amount of blood that goes through your circulatory system in 1 minute. Other systems in your body also respond. Your blood pressure decreases to allow the extra blood volume to flow. But some women develop high blood pressure instead. This can put more stress on your heart, especially if you have a pre-existing heart condition.
Changes in your heart and vascular system can also happen during labor and delivery. Large amounts of blood move from your uterus into your circulation, as your uterus contracts. This causes changes in your blood pressure, heart rate, and cardiac output. If you get an epidural or spinal anesthesia, this can also cause your blood pressure to decrease.
After childbirth, your cardiac output increases and your heart rate slows down. You can have heavy blood loss with delivery. This can change your heart rate, blood pressure, and cardiac output.