During pregnancy, a mom-to-be’s circulatory system goes through rapid and dramatic changes, says Oliver W. Jones, MD, a maternal-fetal medicine specialist in Denver. Blood volume starts ramping up as early as five weeks’ gestation, and by the end of the third trimester, it will have increased by about 1.5 liters—all to meet your body’s demand for more oxygen and to support the growing uterus, placenta and breast tissue.
Expectant mamas can also look forward to a rise in water weight. Your baby-making body will house an additional 6.5 to 8.5 liters. (That’s around 2 gallons!) Some of this water gain, according to Jones, contributes to fluid outside the blood vessels, which you and your ankles know all too well as swelling.
As the uterus continues to expand, it puts the squeeze on mama’s veins, impairing circulation, particularly for blood returning to your heart. Because blood flow is slowed down, the body parts farthest from your heart—like hands and feet—are most likely to swell.
Poor circulation, which commonly takes shape as varicose veins, occurs in about 20 percent of women. But having a bun in your oven isn’t the only factor that comes into play. Jones points to family history, activities that involve standing for long periods of time, obesity and advanced age as additional risk factors.