It's not uncommon to have a drop in blood pressure during pregnancy. Many women don't realize that pregnancy can have an effect on blood pressure. It occurs because the circulation expands during pregnancy and hormonal changes cause the blood vessels to dilate, leading to a lowering of blood pressure. The blood pressure begins to fall in early pregnancy and is usually at its lowest sometime in the middle of the second trimester. For many clinicians, low blood pressure is defined by the blood pressure that gives a person the symptoms described below and not by a standard measurement.
Not surprisingly, women may experience symptoms of low blood pressure during pregnancy. These symptoms are similar to symptoms that anyone with low blood pressure might feel. Most commonly, symptoms of low blood pressure in pregnancy include dizziness and even fainting. The lightheadedness can be worse when standing up suddenly or rising from a reclining position.
The normal drop in blood pressure that occurs with pregnancy typically does not cause the symptoms of severe hypotension that occur with shock. In patients with sepsis or profound blood loss, a severe drop in blood pressure can result in organ damage such as stroke, kidney failure, and heart attack.
The extent to which blood pressure drops is variable, but in most pregnant women, the systolic pressure drops by 5 to 10 mmHg. The diastolic pressure can drop up to 15 mmHg in a normal pregnancy. These lowered pressures usually last during the pregnancy and return to original levels afterward.
Pregnant women who are experiencing dizziness due to low blood pressure can take steps to minimize the symptoms and promote safety, such as the following:
- Sitting or lying down if they feel faint, to avoid falls
- Avoiding standing up too fast from a seated or lying position
- Lying on the left side, to increase blood flow to the heart
Of course, it's important to see one's health care professional if dizziness worsens or is associated with other troubling symptoms. A woman should access emergency care if she experiences dizziness or "fainting" with serious symptoms like bleeding, severe headache, vision changes or blurring, chest pain, shortness of breath, and weakness or numbness, particularly on one side of the body.
"Pregnancy and Dizziness." American Pregnancy Association. March 2007.
Cunha, John P. and Jay W. Marks. "Low Blood Pressure (Hypotension)." MedicineNet. 4 Oct. 2010.