Pregnancy brings many changes in a woman’s body; the size of the tummy is the most noticeable one. However, there are many other amazing changes that a pregnant woman undergoes that are not obvious, but are a miraculous process happening in the background. One such aspect is the changes in blood volume in pregnancy and the associated cardiovascular changes. Continue reading to know more about it and its effect on the organ system.
The body undergoes many changes during pregnancy to support the growing fetus. One major change is that it increases blood flow in the body. The extra blood is made for two reasons: to supply nutrients and oxygen to the fetus through the placenta and to support your kidneys, heart, uterus, breasts, skin, and other organs that work harder during pregnancy.
Typically, a healthy woman has approximately 4.3 L of blood in her body. A healthy pregnancy can raise this by about 40 to 50%. A study conducted on pregnant women found a 6% increase in the first trimester, a 26% increase in the second and a 48% increase immediately after birth. If you are pregnant with multiples, the body needs more blood. Pregnant women with twins may have more than 67% more blood compared to before pregnancy. That is 10 to 20% more than in a pregnancy with a single baby.
● The body has RAAS (renin-angiotensin-aldosterone system), a natural system that controls blood volume and blood pressure. This system is triggered when the pregnancy hormones increase, especially in the last stage of pregnancy.
● This increases the production of angiotensinogen, a protein that plays a crucial role in regulating fluid balance and blood pressure in the body.
● The kidneys detect a reduction in blood pressure due to hormonal changes and release renin to regulate it.
● It triggers a chain reaction where angiotensinogen is converted to angiotensin II. This tightens the blood vessels and raises the blood pressure.
● It also signals the adrenal glands to release the aldosterone hormone, which makes the kidneys retain more salt instead of releasing it through urine.
● More salt in the blood means it pulls more water into the blood vessels, increasing blood volume.
● As you approach your third trimester, hormones like estrogen gradually increase, which in turn releases more angiotensinogen and renin, resulting in increased aldosterone and blood volume.
● The release of prorenin by the ovaries and placenta activates RAAS and further increases blood volume.
To summarise, the RAAS system is more active during pregnancy, which leads to increased aldosterone (a hormone that retains salt in the body). When the blood contains more sodium, it draws more water, thereby increasing blood volume in the body. This extra blood adds more pressure on the blood vessels and heart, which is why pregnant women gain 10 to 12 kg during pregnancy.
Anaemia is a common blood disorder during pregnancy and, if left untreated, can lead to maternal deaths. It is a condition where the body has an increased red blood cell mass but is less than the plasma volume, leading to physiological anaemia. This can be caused by poor diet, bleeding or when RBCs are destroyed early. However, it is a common disorder in pregnancy if the mother does not consume enough iron, folate and vitamin B12. To support the production of RBCs for the mother and the growing fetus, she should ensure that she consumes the above nutrients through diet or supplements.
The circulatory system, which involves the blood, blood vessels and the heart, changes during pregnancy to meet the demands of the growing baby.
The amount of blood pumped per minute, or cardiac output, increases by up to 31% during the early third trimester, supporting the growth of the uterus, placenta, breasts, kidneys and various other organs. To maintain this output, the heart’s muscle walls thicken, and the heart rate increases by 10 to 20 beats per minute. The uterus expands, and the heart shifts up slightly as the abdominal organs get pushed. After birth, the heart returns to its pre-pregnancy position and size.
To allow increased maternal circulation, blood vessel dilation is essential. Pregnancy hormones, such as progesterone and estrogen, help blood vessels dilate and reduce blood pressure. It typically drops in the first two trimesters and returns to normal after delivery. Women with high BMI have high blood pressure, increasing pregnancy risks like-
● Preeclampsia: A few women (3 to 5%) have high blood pressure after 20 weeks of pregnancy and are known as preeclamptic. It is diagnosed when blood pressure is more than 140/90 mmHg and there is protein in the urine. It causes symptoms such as swelling, headache and vision problems. If left untreated, it can cause kidney damage, stroke and preterm birth. Typically, women deliver by 37 weeks to prevent complications to the baby. Maintaining a healthy BMI reduces the risks, as it is the leading cause of fetal and maternal death.
● Heart disease: Pregnancy blood production can reveal undiagnosed heart conditions as the circulatory system undergoes strain. Up to 4% of expectant mothers may have cardiac problems like cardiomyopathy or valve disease, especially those with preexisting conditions like diabetes and obesity.
● Blood clots: Blood clots form easily during pregnancy as preparation for childbirth. But it puts women at a risk of thrombosis, pulmonary embolism or stroke. This is more likely to occur in women who have blood vessel damage, slower or thicker blood flow. To prevent thrombosis, stay active, avoid smoking, wear compression stockings, and elevate your legs. Varicose veins are common and increase the risk of clot formation.
● Stroke and DIC: Stroke occurs in 30 out of 100,000 pregnancies and is dependent on age. Another issue that is rare but dangerous is DIC (disseminated intravascular coagulation), which involves bleeding and clotting and is triggered by risks like infection or preeclampsia.
The increase in blood volume during pregnancy is a complex, well-tuned process that ensures the growing fetus and the mother receive the needed nutrients and oxygen. While most bodily changes occur without any external intervention, they depend on good nutrition, a conducive environment and regular monitoring. By understanding these changes, pregnant women can have a healthy pregnancy and prepare for childbirth.
