Low blood pressure, called hypotension in the medical field, occurs when the heart, brain and other parts of the body do not get enough blood after the heart pumps it out, explains Drugs.com. Some women have low blood pressure before pregnancy but most women experience at least a slight decrease in blood pressure as a result of the bodily changes from pregnancy. Most cases are mild but if fainting occurs, medical treatment is necessary.
Weight of the Uterus
One common type of hypotension that occurs during pregnancy is supine hypotension. This occurs when a woman lies flat on her back. The American Pregnancy Association explains that the weight of the uterus rests on the major blood vessels in the body and slows or stops the transport of blood to some areas of the body. This is a temporary type of hypotension that can be alleviated by sleeping on the side or at an incline.
Rising Suddenly
Postural hypotension can occur in all individuals but it is very common in pregnancy. When a woman stands quickly from sitting, squatting or kneeling gravity can slow the speed of blood travel, creating a dizzy sensation from reduced blood pressure, explains the American Pregnancy Association. To avoid this temporary type of blood pressure drop a woman can change position more slowly to reduce the impact gravity has on the blood flow.
Dehydration
When an individual becomes dehydrated she can trigger hypotension, explains MayoClinic.com. This is because water is a critical component of blood cell production. A pregnant woman has a greater blood volume to support herself, the placenta and the baby. When the water levels are too low the heart is still pumping blood but it may not be a high enough quantity to provide for all the parts of the body, which results in hypotension. Pregnant women should drink at least 64 oz. of water per day and sometimes more depending on her health care provider's recommendations. Most women urinate more frequently due to the kidneys eliminating waste from the baby and due to increased pressure on the bladder from the weight of the womb. Frequent urination means a woman must replenish the fluids in her body.
Shock
Severe hypotension can occur due to a sudden loss of blood, such as following the birth of the baby. Drugs.com refers to this severe decrease in blood pressure as shock. Most women recover fully from hypotension of this type due to being monitored closely after the baby has arrived. Blood loss is not always significant enough to cause shock.
