From the Research
During pregnancy, the uterus undergoes significant changes to support the growing fetus, including an increase in size, changes in the myometrium and endometrium, and increased blood flow, all of which are crucial for a healthy pregnancy and delivery. These changes are driven by hormonal fluctuations, particularly estrogen, progesterone, and human placental lactogen 1. The uterus expands from a pear-sized organ weighing about 70 grams to weighing approximately 1,100 grams at term, with its capacity increasing from about 10 ml to 5 liters. This growth occurs through hypertrophy of existing muscle cells rather than formation of new cells.
Some key changes include:
- The myometrium (muscular layer) thickens initially but then stretches and thins as pregnancy progresses
- Blood flow to the uterus increases substantially, with uterine arteries enlarging to deliver about 500-750 ml of blood per minute at term
- The endometrium transforms into the decidua, which develops three distinct layers: the decidua basalis (beneath the placenta), decidua capsularis (covering the gestational sac), and decidua parietalis (lining the remainder of the uterine cavity)
- The cervix softens and develops increased vascularity due to higher estrogen levels, forming a mucus plug that seals the cervical canal to protect against infection.
Understanding these changes is essential for managing pregnancy and preventing complications, as highlighted in recent studies on physiological changes during pregnancy 2, 3, 4. While older studies provide valuable background information 5, the most recent and highest quality study 1 emphasizes the importance of recognizing these changes to support the health of both the mother and the fetus.