Pregnancy changes almost every organ system so the mother can supply a growing fetus. Knowing what is normal in pregnancy helps you spot what is not.
Heart and blood
Blood volume rises about 40 to 50 percent and cardiac output rises with it, while the heart rate goes up by about 10 to 20 beats per minute. Plasma rises more than red cells, so a mild dilutional anemia is normal.
Blood pressure
Blood pressure dips in the second trimester and returns to baseline near term. Lying flat on the back late in pregnancy lets the uterus press on the vena cava and can drop the pressure.
Lungs
Breathing gets deeper, so minute ventilation rises and the normal CO2 falls. The growing uterus pushes the diaphragm up, which can cause mild shortness of breath.
Kidneys and gut
Kidney blood flow and filtration rise, so creatinine normally falls. Progesterone relaxes smooth muscle, which slows the gut and causes heartburn and constipation.
Clotting
Clotting factors rise to protect against bleeding at birth. This also raises the risk of deep vein thrombosis and pulmonary embolism.
| Measure | Change | Practical point |
|---|---|---|
| Heart rate | Up 10 to 20 per minute | Mild tachycardia can be normal |
| Blood pressure | Lower mid pregnancy | 140/90 or higher is never normal |
| Hemoglobin | Slightly lower | Mild dilutional anemia |
| Creatinine | Lower | A normal adult value may mean kidney trouble |
At the bedside
Tilt a patient in late pregnancy to the left, or push the uterus to the left by hand, to take pressure off the vena cava, especially during CPR. A blood pressure of 140/90 or higher after 20 weeks raises concern for preeclampsia.
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Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).