03.01 Physiological Changes

In this lesson I will explain the physiological changes that occur in pregnancy in a more understandable way

Physiological changes are those changes that occur to the bodies functions. So not the physical looks but how it functions. The changes are normal and caused by mostly hormones (Estrogen, progesterone, HCG, Aldosterone), growing and expanding uterus, and an increase in blood volume. These physiological changes affect the heart, respiratory, musculoskeletal, gastrointestinal, and renal system.


A head to toe assessment should be done to look for any changes. The patient should be Interviewed to identify changes she has noticed and if she has any concerns. Reassuring the patient that the changes are normal can be comforting for the patient.

It is important to know the main cause of these changes. Hormones are a large cause and the ones really involved are estrogen, progesterone, HCG, aldosterone. Estrogen is responsible to an increase in vascularity and nasal congestion. Progesterone is responsible for keeping the body pregnant. So it slows everything down like the gastrointestinal tract. This cause constipation and bloating. It also keeps the uterus from contracting to maintain that pregnancy. HCG is increasing and doubling as the pregnancy gets further along. This is going to cause the nausea and vomiting for the gastrointestinal tract. Aldosterone increases the plasma volume. This will be more work for the heart but helpful post delivery when there is a lot of bleeding. The respiratory system is changes because of an increase in oxygen consumption. Also because of the hormone estrogen there is an increase in nasal congestion and stuffiness. Nosebleeds are common because of this. The gastrointestinal system is going to slow down. This is mainly because of which hormone? Yes, progesterone. So this is going to cause constipation, nausea/vomiting, and bloating. The renal system changes in ways that there is more frequent urination. This is because not just the weight of the uterus/fetus and it grows but also because of rising hormone levels. UTI risk is greater because of the weight of the uterus can cause blockade so not all the unit is able to exit. You can see in this picture how there is a small area to grow a baby. This causes the respiratory system to be crunched and the GI system to be bothered easily. Also with aldosterone increasing the plasma levels and the weight of the uterus hypotension is a big side effect. So let’s switch and talk about this cardiovascular system in more detail.


The cardiovascular system is changing as there is increasing blood volume. This picture gives a better visual. You can see blood volume increases 30-50%. In the third trimester the plasma amounts really increase and this causes anemia. The plasma amounts increase a lot where the red blood cells increase only a small amount. This causes the hematocrit to go down. Because of the increasing volume, murmurs might be heard and are normal. Edema will also occur as well as an increase in pulse by 10-15 BPM. Blood pressure also is reduced in the second trimester. hormonal changes cause the blood vessels to dilate so the blood pressure lowers. The blood pressure is usually at its lowest sometime in the middle of the second trimester. These changes can cause a lightheaded feeling and of course passing out can cause some uneasiness to the patient so just an an example of one of the changes that could concern the patient. The musculoskeletal system changes because of hormones and the uterus. So a hormone called relaxin causes the system to relax. It allows for the system to open up and allow room for the growing fetus. Also we have posture changes. We see lumbar lordosis because of the shift in the center of balance and the growing uterus. The hematologic system sees changes in coagulopathies. These increase, which are needed to clot off and stop too much bleeding post delivery but also increase the risk for DVTs.


There is not much therapeutic management. We want to treat any discomfort that changes are causing if possible. Some of these changes are a band to lift the growing uterus and relieve back discomfort, medications for GI discomfort and diet to manage constipation can also help such as ondansetron (zofran).

It is important that they know these are normal changes and what to expect. We want to give them ways to improve symptoms. Nausea will be a big complaint so ways to improve symptoms are to eat crackers before rising from bed, don’t let stomach get empty. It is also Importance of maintaining correct posture to prevent musculoskeletal discomfort and back pain. We want to tell them when to be concerned and symptoms to call about. These would be frequent vomiting causing weight loss, signs of blood clots, DVTs and UTI symptoms.


Reproduction is a concept because the pregnancy is causing the physiological symptoms to happen. Hormonal regulation is the last concept because hormones are a big cause for all the changes that are occuring.
Let’s review some of the main key points to remember. Many of these changes are due to hormones which are estrogen, progesterone, HCG, and aldosterone. The expanding uterus (and therefore pelvis) will cause musculoskeletal discomforts. There is an increase in oxygen consumption which will affect the respiratory system. We have that increasing circulatory blood volume which is putting more work on the heart. Last it is important to remember and remind the patient that these are normal pregnancy changes.

Make sure you check out the resources attached to this lesson. Now, go out and be your best selves today. And, as always, happy nursing.