Your body goes through many changes during pregnancy -- many that you can see and feel and many that you cannot. Your cardiovascular system, which goes through many changes during pregnancy, includes the heart, blood, veins and arteries. It is responsible for transporting nutrients, metabolic wastes, hormones and gases to and from all the cells of the body and must go through some changes to support your needs as well as those of your growing baby.
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Starting when you are about six weeks pregnant, your blood volume begins to increase and continues to do so until about 32 weeks gestation. This is necessary in order to facilitate the exchange of respiratory gases and nutrients between you and the baby. This increase in blood volume also minimizes the impact of blood loss during delivery. The amount of increase in blood volume is dependent on your size, number of pregnancies and deliveries and the number of fetuses you are carrying.
The actual composition of your blood will also change during pregnancy. You will experience an increase of about 40 to 50 percent in blood plasma. Additionally, your red blood cell concentration will increase by about 20 to 30 percent. Because your plasma increases more so than your red blood cells it is necessary to supplement with iron and folic acid in order to maintain the ideal levels of hemoglobin.
The size of the heart as well as its position also changes with pregnancy. Because of the expanding uterus, the diaphragm is pushed upwards which in turns pushes the heart further up in the chest cavity. The actual size of your heart increases by about 12 percent during pregnancy.
Cardiac output is the amount of blood pumped out by the heart in one minute. Similar to blood volume, there is a 30 to 40 percent increase in cardiac output during pregnancy. The PregnancyZone.com estimates that your cardiac output will go from 6.7 liters per minute when you first conceive to 8.7 liters per minute at delivery It will peak about half-way through gestation and maintain this elevated level until delivery. This increase in cardiac output can be traced to the increase in heart rate among pregnant women as well as the increase in heart size.
In a normal pregnancy, your blood pressure will remain about the same as your non-pregnant state during the first trimester. It will then most likely drop during mid-pregnancy and return to your normal values during the final months of gestation. If you had high blood pressure before pregnancy, you are most likely going to have high blood pressure during pregnancy. Physicians get concerned when your blood pressure greatly increases above your normal levels in the second or third trimester. MayoClinic.com says that an elevated blood pressure can limit the amount of blood and oxygen your baby is receiving, while increasing your risk of premature delivery and the risk of the placenta pulling away too early. It also notes that a woman who suffers from high blood pressure during pregnancy may be at an increased risk for cardiovascular disease later in life.