Some changes a woman experiences during pregnancy lead to a perfectly acceptable drop in blood pressure. The American Pregnancy Association explains that rising hormones cause blood vessels to relax and widen. This allows blood flow to the baby but slows the blood’s return to the mother’s brain. This can cause dizziness and a drop in blood pressure. Other factors in pregnancy can exacerbate hypotension, or lower blood pressure, to dangerous levels.
Postural Hypotension
Postural hypotension affects nearly everyone at some point in life. In pregnant women, this type of hypotension is exacerbated by the widened blood vessels and increased blood volume. Postural hypotension occurs when an individual changes position quickly, such as standing from a kneeling, squatting or sitting position. The American Pregnancy Association attributes the pressure drop to gravity, forcing blood to move even slower to the woman’s brain. The result is dizziness that can lead to feeling faint.
Supine Hypotension
Supine hypotension is usually experienced some time after the 20th week of pregnancy when the uterus has grown significantly. A woman experiences the dizziness and general discomfort from this decrease in blood pressure when she lies flat on her back. The American Pregnancy Association explains that this is due to the uterus putting pressure on the major blood vessels in the body and slowing the circulation of blood. Pregnant women can avoid this by resting on their side instead of flat on their back.
Ectopic Pregnancy
An ectopic pregnancy occurs when the fertilized egg attaches somewhere other than the uterus. The American Congress of Obstetricians and Gynecologists points out that the fallopian tube is the most common location for this type of pregnancy. An ectopic pregnancy must be treated medically because of the risk of the egg rupturing away from the tissue where it has attached. A rupture can cause internal bleeding. A sudden decrease in blood pressure is a characteristic indicator of a ruptured ectopic pregnancy. A woman may feel faint or lose consciousness as a result of the internal bleeding.
Medications
Numerous medications cause a reduction in blood pressure. If a pregnant woman is prescribed such a drug, it is likely that her doctor will monitor her blood pressure closely. The March of Dimes indicates that several medications given to stop pre-term labor can decrease blood pressure. Examples include calcium channel blockers and beta-mimetics, both of which slow blood flow by tightening the blood vessels. These effects serve the purpose of slowing contractions but require monitoring of the mother and baby for adverse reactions. Other types of medications that cause a decrease in blood pressure aren't usually used in pregnancy unless absolutely necessary, such as tricyclic antidepressants, beta blockers, diuretics or medications for the treatment of Parkinson's disease.
