The human body undergoes remarkable transformations during pregnancy to support the development of new life. These changes are not limited to outward appearances; significant internal adaptations occur as well. The internal organs of a pregnant person shift and adjust to accommodate the growing uterus and fetus.
The Expanding Uterus
The uterus, typically the size of a lemon or a pear before pregnancy, undergoes an extraordinary increase in size and weight. Before pregnancy, it weighs about 1 ounce and is 3 inches long and 2 inches wide. By the end of pregnancy, it can weigh up to 2 pounds and expand to the size of a watermelon, extending from the pubic area up to the rib cage.
This expansion is stimulated by hormones. Around 12 weeks of gestation, the uterus becomes comparable in size to a grapefruit and begins to grow out of the pelvis. By the second trimester, it no longer fits within the pelvis and moves midway between the navel and breasts. The uterus can ultimately reach a capacity 500 to 1000 times greater than its non-pregnant state.
Organ Displacement and Its Effects
As the uterus grows, it displaces the surrounding abdominal organs to make room for the developing fetus. They become compressed and shift upwards and sideways. This physical relocation is a primary reason for many common pregnancy symptoms.
The bladder, located directly beneath the uterus, experiences increased pressure from early pregnancy. This compression leads to a more frequent urge to urinate. The growing uterus can also pull on the pelvic floor muscles, which can sometimes result in bladder leakage, especially when coughing, sneezing, or laughing.
The stomach and esophagus shift upwards as the uterus expands. This upward displacement, combined with hormonal changes that relax the lower esophageal sphincter, contributes to heartburn and indigestion. The stomach’s position can change, lying across the top of the uterus instead of its usual downward orientation.
The diaphragm is pushed upwards by the expanding uterus. This reduces the space available for the lungs to fully expand, leading to shortness of breath, particularly in later pregnancy. This sensation can be more noticeable in the third trimester as the uterus reaches its highest point near the rib cage.
The intestines are pushed to the sides and upwards, becoming compressed against the diaphragm and abdominal wall. This displacement, along with hormonal changes that slow down digestion, can affect bowel regularity. Constipation is a common complaint, as the movement of food through the intestinal tract is prolonged.
The Postpartum Return
After childbirth, the body begins a gradual process of returning to its pre-pregnancy state, known as involution. The uterus starts to contract and shrink almost immediately. These contractions, often felt as afterpains, help to expel the placenta and reduce bleeding.
The uterus typically reduces to the size of a grapefruit within the first few days postpartum. It continues to shrink, reaching approximately the size of a pear by two weeks after delivery and returning to its pre-pregnancy size within about six weeks. As the uterus diminishes, the displaced organs, including the bladder, stomach, lungs, and intestines, gradually shift back into their original locations. While immediate improvements in breathing and comfort may be noticed, a complete return to normal positioning can take several months.