Swelling during pregnancy is caused primarily by a massive increase in blood volume and fluid retention, driven by hormonal shifts that change how your blood vessels handle fluid. Your plasma volume expands by about 45% to support the growing baby, and much of that extra fluid ends up in your tissues, especially in the legs, ankles, and feet. This is one of the most common pregnancy symptoms, and in most cases it’s completely normal.
Why Your Body Retains So Much Fluid
Pregnancy demands a dramatically larger blood supply. Your body produces far more blood plasma than red blood cells, which thins the blood and increases the total volume of fluid circulating through your system. At the same time, rising progesterone levels trigger a chain of changes in your blood vessel walls. Progesterone stimulates the production of a protein that increases capillary permeability, meaning the tiny blood vessels throughout your body become “leakier.” Fluid that would normally stay inside the bloodstream seeps more easily into surrounding tissues, and gravity pulls it downward toward your feet and ankles.
Your kidneys also play a role. Hormonal signals during pregnancy cause the kidneys to retain more sodium, and sodium holds onto water. The result is a steady buildup of fluid in your tissues that becomes more noticeable as the day goes on, especially if you’ve been standing or sitting in one position for a long time. Most women notice swelling goes down overnight when they sleep and fluid redistributes more evenly.
How the Growing Uterus Makes It Worse
As pregnancy progresses into the third trimester, a mechanical factor compounds the hormonal one. The enlarged uterus presses on the inferior vena cava, the large vein that carries blood from your lower body back to your heart. This vein runs along the right side of your spine, and when the weight of the uterus compresses it, blood return from the legs slows significantly. The backed-up pressure forces more fluid out of the veins and into the tissues of your legs and feet.
This is why swelling tends to be worst in the final weeks of pregnancy and why lying on your left side helps. Shifting to the left takes the uterus off the vena cava and improves blood flow back to the heart. Women who lie flat on their backs in late pregnancy sometimes feel lightheaded for the same reason: the compressed vein reduces how much blood reaches the heart, lowering blood pressure temporarily.
When Swelling Typically Appears
Mild swelling can start in the second trimester, but it becomes much more noticeable in the third trimester as blood volume peaks and the uterus reaches its largest size. The pattern is predictable: worse in the evening, better in the morning. Hot weather, long periods of standing, and high sodium intake all amplify it. Soon after delivery, the extra fluid clears fairly quickly as hormone levels drop and blood volume returns to normal.
Swelling Beyond the Ankles
Fluid retention doesn’t just affect your feet. The extra volume increases pressure in blood vessels throughout the body, and in tight anatomical spaces, that pressure can compress nerves. The wrist is a common trouble spot. Nine tendons and the median nerve pass through a narrow channel called the carpal tunnel, and pregnancy-related swelling can squeeze that nerve enough to cause tingling, numbness, or pain in the hands and fingers. This pregnancy-related carpal tunnel syndrome is temporary and usually resolves after delivery, but it can be uncomfortable enough to disrupt sleep.
Swelling in the hands and face is also possible and worth paying attention to, not because hand swelling is always dangerous, but because the pattern matters when distinguishing normal fluid retention from a complication like preeclampsia.
When Swelling Signals a Problem
Normal pregnancy swelling is gradual, affects both sides of the body equally, and responds to rest and elevation. Two conditions can cause swelling that looks and behaves differently.
Preeclampsia is a serious pregnancy complication diagnosed after 20 weeks of gestation when blood pressure rises to 140/90 mmHg or higher and protein appears in the urine. Sudden, severe swelling in the hands and face is one of the warning signs the World Health Organization lists alongside persistent headaches, vision changes, and upper abdominal pain. The swelling from preeclampsia tends to come on quickly rather than building slowly over weeks.
Deep vein thrombosis (DVT) is a blood clot in a deep leg vein. Pregnancy increases clotting risk, so this is a real concern. The key difference from normal pregnancy swelling is that DVT typically affects only one leg. Signs include pain or cramping that starts in the calf, warmth over the affected area, and skin that looks red or purple. Normal pregnancy edema is symmetrical. If one leg suddenly swells more than the other, that warrants prompt medical evaluation.
Practical Ways to Reduce Swelling
You can’t eliminate pregnancy swelling entirely because it’s a built-in part of how your body supports the pregnancy, but several strategies make a real difference in comfort.
- Compression socks: Graduated compression socks gently squeeze the legs to help push fluid back into circulation. For mild swelling, 15 to 20 mmHg pressure is usually enough. If you have varicose veins or more significant swelling, 20 to 30 mmHg provides stronger support. Put them on in the morning before swelling builds.
- Elevation: Propping your feet above heart level for 15 to 20 minutes several times a day lets gravity work in your favor, moving fluid out of the legs and back toward the heart.
- Movement: Walking, ankle circles, and calf raises activate the muscle pump in your lower legs, which physically pushes blood upward through the veins. Sitting or standing still for long stretches allows fluid to pool.
- Sleep position: Lying on your left side at night takes pressure off the vena cava and improves venous return from the legs.
- Sodium intake: UW Medicine recommends keeping sodium between 2,000 and 3,000 mg per day during pregnancy, with a target around 2,300 mg. You don’t need to slash salt drastically, but avoiding heavily processed foods and restaurant meals helps prevent the sodium spikes that worsen fluid retention.
- Water intake: It sounds counterintuitive, but staying well hydrated helps your kidneys regulate fluid balance more efficiently. Dehydration can actually trigger your body to hold onto more water.
Tight rings, socks with restrictive bands, and shoes that have become too snug can all worsen discomfort by trapping fluid below the constriction point. Switching to looser footwear and removing rings early (before fingers swell enough to make removal difficult) saves a lot of frustration in the third trimester.