Physiological cardiovascular adaptation in pregnancy
The cardiovascular system adapts during pregnancy towards the occurrence of changes. Although changes in the cardiovascular system are seen early in the first trimester, progress to the second and third trimesters of cardiac output increases by approximately 40% than in non-pregnant women. Cardiac output increased from the fifth week of pregnancy and reached the maximum level around the 32nd week of pregnancy.
It is only slightly increased until the period of labor, birth, and the postpartum period. About a 50% increase in cardiac output has occurred during the 8th week of pregnancy. Despite the increase in cardiac output due to an increase in stroke volume and heart rate, the most important factor is stroke volume. This increases by as much as 20% to 50% more than in non-pregnant women. Changes in heart rate are very difficult to calculate, but it is estimated that there is an increase of around 20% seen in week 4 of pregnancy.
In the second trimester, aortocaval compression by uterine enlargement becomes progressively important, reaching a maximum point at weeks 36 and 38. Further, it can reduce the displacement of the fetal head position to the pelvis. Cardiovascular is everything related to heart and blood circulation. There are two types of circulatory systems namely the opened circulatory system, and the closed circulatory system.
In the circulatory system, part of the performance of the heart and blood vessel tissue (cardiovascular system) is formed. First, blood carries oxygen from the lungs to cells and carbon dioxide in different directions. Second, it is transported from digestive-derived nutrients such as fat, sugar, and proteins from the digestive tract in each tissue to be absorbed, processed or stored.
Changes in physiology and anatomy develop in many organ systems with the occurrence of pregnancy and childbirth. Initial changes occur in metabolic changes due to the presence of the fetus, placenta, and uterus. Also, there is an increase in pregnancy hormones such as progesterone and estrogen. The next change, in the third trimester of pregnancy, is anatomical changes. These are caused by pressure due to the development of the uterus.
Changes in the cardiovascular system during pregnancy are characterized by an increase in blood volume, cardiac output, heart rate, stroke contents, and decreased vascular resistance. Hemodynamics that first changes during pregnancy are an increase in heart rate. Starting between two to five weeks of pregnancy until the third trimester. The contents of a stroke and heart rate increase in the early age of pregnancy and decrease after delivery. Other changes that occur are low arterial blood pressure and increased plasma volume, blood volume, and volume of red blood cells. While, central venous pressure (pressure in the right atrium in the large vein in the thoracic cavity) is constant, 3-8 cm.
Cardiac output also increases during pregnancy. It is about 30-40% higher than non-pregnant conditions in the first trimester even increases 40-50% in the third trimester. Increased cardiac output in early pregnancy is influenced by estrogen and causes many parts of the cardiovascular system to be dilated, such as cardiac and aortic dilatation, renal vascular resistance, placental resistance, and dilated venous system. All changes support perfusion to the body of pregnant women. Cardiac dilation increases direct stroke, while aortic dilatation increases susceptibility to the aortic vessel wall. Peripheral dilation increases blood flow, and venous dilatation increases blood volume.
Cardiac output depends on heart rate and stroke intensity. Increased cardiac output increases the burden on the heart, especially if it is associated with an increase in heart rate. In this case, cardiac energy expenditure increases when the oxygen supply decreases. Increased cardiac energy expenditure is caused by an increase in blood flow rates, especially turbulence in the case of valve stenosis. Adaptation of the cardiovascular system during pregnancy increases the risk of cardiovascular disorders. In some cases, pregnant women with a history of heart disease before pregnancy can potentially get heart failure.
The volume of the blood
During pregnancy, the anatomy of the cardiovascular system changes, including:
- Thickening of the ventricular wall muscles, occurring in the first trimester
- The place of dilation (widening) in the heart because the volume in the abdominal cavity (abdomen) increases causing hypertrophy of the heart and the position of the heart to shift
- In phonocardiogram, there are splitting (additional heart sounds), systolic murmurs and changes in blood pressure.
These changes make the need for pregnant women to supply Fe increase by around 500 mg% per day. They often experience physiological anemia (normal hemoglobin state 12 grams% and hematocrit 35%). Maternal blood volume will increase progressively at 6 – 8 week of gestation and will reach a maximum in pregnancy close to 32-34 weeks. Increased blood volume includes the volume of plasma, red blood cells, and white blood cells. Plasma volume increases by 40-50%, while red blood cells increase by 15-20% which causes physiological anemia. Because of hemodilution, blood viscosity decreases by approximately 20%. The exact mechanism for increasing blood volume is unknown, but some hormones such as rennin-angiotensin-aldosterone, atrial natriuretic peptide, estrogen, progesterone may play a role in this mechanism.
In the process of pregnancy, along with the gestational age, the platelet count decreases. This change is not only to protect against catastrophic bleeding but also predispose the thromboembolic phenomena. The placenta is rich in thromboplastin. If placental abruption occurs, it will be a risk of Disseminated Intravascular Coagulation.
Increased blood volume has several important functions:
- To maintain the need for increased circulation because there are an enlarged uterus and foeto-placental unit.
- Fill in increased vein reservoir.
- Protect the mother from bleeding during childbirth.
- During pregnancy, the mother becomes hyper coagulopathic.
However, eight weeks after giving birth, the blood volume returns to normal.
About blood pressure
During pregnancy, the frequency of heart rate is rather increased, as the pulse can reach 88 pulses per minute, especially in gestational age of 34-36 weeks. Plasma volume during pregnancy also increases. Increased plasma volume starts in the final trimester and reaches its peak in weeks 32 to 34, then settles during the final trimester of pregnancy. At that time, plasma volume increased by 22% compared to the time before pregnant. Increased plasma volume continues after 12-24 hours postpartum. After the process has passed, the plasma volume will decrease again to the normal of plasma volume as before pregnancy.