About 8 out of 10 pregnant women develop noticeable swelling at some point during pregnancy, most commonly in the legs and feet. It typically appears in the late second or third trimester and results from a combination of increased blood volume, hormonal shifts, and physical pressure from the growing uterus. In most cases it’s a normal, expected part of pregnancy, though certain patterns of swelling can signal something more serious.
Your Blood Volume Nearly Doubles
The single biggest driver of pregnancy swelling is a dramatic expansion in how much fluid your body carries. Plasma volume, the liquid portion of your blood, increases by 50 to 60 percent over the course of a healthy pregnancy. Total blood volume rises by about 45 percent, adding roughly 1,200 to 1,600 milliliters above your pre-pregnancy baseline. Most of this increase happens by around 34 weeks. At the same time, your extracellular fluid (the fluid sitting in tissues outside your blood vessels) increases by 30 to 50 percent. All that extra fluid has to go somewhere, and gravity pulls it toward the lowest points in your body: your ankles, feet, and lower legs.
Hormones That Hold Onto Fluid
Your body doesn’t accumulate all that extra fluid by accident. A hormone called aldosterone, which tells your kidneys to retain sodium and water, climbs to roughly ten times its normal level by the end of pregnancy. That sodium retention is deliberate: your body needs the extra fluid volume to supply adequate blood flow to the placenta.
Progesterone, which also rises steadily throughout pregnancy, acts as a natural counterbalance. It competes with aldosterone at the kidney, partially blocking its effects so that fluid retention doesn’t spiral out of control. The result is a managed increase in body fluid that keeps both you and the baby supplied with blood, but also leaves your tissues waterlogged, especially in the legs. This hormonal tug-of-war is why swelling tends to worsen gradually as pregnancy progresses and hormone levels climb higher.
The Uterus Presses on Major Veins
By the third trimester, your uterus is large enough to physically compress the inferior vena cava, the large vein that carries blood from your legs back up to your heart. When that vein is partially squeezed, blood pools in the lower extremities and venous pressure in the legs rises progressively. The compression also affects nearby lymphatic vessels, further reducing drainage from the legs.
This effect is worst when you lie flat on your back, because gravity pushes the heavy uterus directly onto the vein against the spine. It’s one reason many women notice their legs feel more swollen after sleeping and why lying on your side (particularly the left side) can relieve the pressure almost immediately. Prolonged standing or sitting also makes it harder for blood to push past the compression point, which is why swelling tends to be most noticeable at the end of the day.
When Swelling Typically Starts
Mild puffiness can appear as early as the late second trimester, but most women notice meaningful leg swelling in the third trimester. That’s when all three factors converge: blood volume is nearing its peak, hormone levels are highest, and the uterus is large enough to compress the vena cava significantly. Swelling often fluctuates day to day depending on activity level, temperature, how much time you’ve spent on your feet, and how much sodium you’ve eaten. Hot weather tends to make it worse because heat dilates blood vessels, pushing more fluid into surrounding tissues.
Practical Ways to Reduce Normal Swelling
Elevating your legs above the level of your heart when you rest helps fluid drain back toward your core. Even propping your feet on a few pillows while sitting makes a difference. Walking and other gentle movement activates the calf muscles, which act as a pump that pushes blood upward through the veins. Simple ankle pumps (pointing and flexing your feet) improve circulation and reduce venous pooling, making them useful when you’re stuck sitting for long stretches.
Compression stockings provide steady external pressure that supports the veins and keeps fluid from settling in the tissues. They’re most effective when you put them on early in the morning before swelling builds up. Sleeping on your left side takes pressure off the vena cava and improves venous return overnight.
On the dietary side, the World Health Organization does not recommend restricting salt specifically to prevent swelling or preeclampsia during pregnancy. Avoiding excessive sodium is considered a healthy practice in general, and women with chronic high blood pressure are encouraged to keep sodium intake low. But aggressive salt restriction isn’t supported by current guidelines for managing normal pregnancy edema.
Swelling That Signals Preeclampsia
Preeclampsia is a serious pregnancy complication involving high blood pressure and organ stress, and it can cause a distinctly different pattern of swelling. The key differences from normal edema: it tends to come on suddenly, it appears in the face and hands (not just the legs), and it may be accompanied by rapid weight gain over just a few days.
Preeclampsia develops after 20 weeks of gestation and is initially identified by blood pressure readings of 140/90 mmHg or higher on two measurements taken at least four hours apart. Severe cases involve pressures of 160/110 mmHg or higher. Other warning signs include persistent headaches, vision changes (blurriness, seeing spots), upper abdominal pain (especially under the right ribs), and nausea or vomiting that starts in the second half of pregnancy.
If your swelling is limited to your lower legs and feet, comes on gradually, and goes down overnight or with elevation, it’s almost certainly the normal physiological kind. Sudden swelling of the face, puffiness around the eyes, or swollen fingers that make it hard to remove rings warrants a prompt call to your provider.
How to Tell DVT Apart From Normal Swelling
Pregnancy increases the risk of deep vein thrombosis (a blood clot in a deep leg vein) because of the same factors that cause normal swelling: slower blood flow, increased clotting factors, and vein compression. The critical difference is that DVT almost always affects one leg only. Normal pregnancy swelling is bilateral, meaning both legs swell roughly equally.
Among pregnant and postpartum women, the left leg is the most common site for DVT, accounting for about 82 percent of cases. Symptoms include pain, warmth, and redness in one leg, often with swelling of the entire leg rather than just the ankle and foot. The tricky part is that pelvic and back pain from a clot higher up in the pelvis can be mistaken for typical pregnancy discomfort, and because edema is so common in pregnancy, swelling alone is a less reliable sign. A leg that is noticeably more swollen than the other, especially if it’s also painful or warm to the touch, needs evaluation.