Hemorrhoids during pregnancy are caused by a combination of hormonal changes, increased blood volume, and physical pressure from the growing uterus. These three factors work together to weaken vein walls, slow blood flow in the pelvis, and create the kind of sustained pressure that causes veins around the rectum to swell. Most pregnant people experience hemorrhoids in the third trimester, though they can appear earlier, especially if constipation is a factor.
How Pregnancy Hormones Weaken Vein Walls
Progesterone, which rises steadily throughout pregnancy, is one of the primary drivers. This hormone relaxes smooth muscle throughout the body, including the muscles that line blood vessel walls. It does this by triggering the release of nitric oxide in the cells that line veins and arteries, which causes those vessels to widen and soften. Progesterone also lowers calcium levels inside smooth muscle cells, further reducing their ability to maintain tone. The result is veins that are more elastic and less able to push blood efficiently back toward the heart.
This relaxation is beneficial in many ways. It helps lower blood pressure and allows blood vessels to accommodate the demands of pregnancy. But it also means the veins around the rectum and anus, which already operate under gravity’s pull and don’t have strong structural support, become more prone to stretching and pooling blood. When those veins swell enough, they become hemorrhoids.
The Weight of a Growing Uterus
As the uterus expands, it presses directly on the inferior vena cava, the large vein responsible for draining blood from the lower body back to the heart. This compression slows the return of blood from the pelvic region, including the veins that drain the large intestine and rectum. The effect is similar to partially kinking a garden hose: blood backs up behind the pressure point, and the veins in the rectal area become engorged.
This mechanical pressure intensifies as pregnancy progresses. By the third trimester, the uterus is heavy enough to create significant compression when you’re sitting or lying on your back. That’s why hemorrhoids are far more common in the final months. Sleeping on your left side can help take some of that pressure off the vena cava, since the vein runs slightly to the right of the spine.
A Major Increase in Blood Volume
Pregnancy increases total blood volume by roughly 45%, though the range can be anywhere from 20% to 100% above pre-pregnancy levels. This extra blood is essential for supporting the placenta and fetus, but it also means more blood is moving through the venous system at all times. Veins that are already softened by progesterone and compressed by the uterus now have to handle significantly more volume. The veins in the rectal area, which are small and sit in a low-pressure zone, are particularly vulnerable to this overload.
Constipation and Straining
Constipation is one of the most direct triggers for hemorrhoids during pregnancy, and pregnancy makes constipation far more likely. Hormonal shifts slow down the entire digestive process, meaning stool sits in the intestines longer and becomes harder and drier. The extra weight of that backed-up waste presses on the surrounding veins, reducing blood flow. Then, when you strain to have a bowel movement, you’re pushing blood into the rectal veins with force, stretching them further.
This straining is often the moment a hemorrhoid actually forms or becomes symptomatic. The vein walls, already weakened and overfilled, bulge outward under the added pressure. If this happens repeatedly over days or weeks, the swelling becomes persistent. Iron supplements, which are commonly prescribed during pregnancy, can make constipation worse and compound the problem.
Sitting and Standing for Long Periods
Prolonged sitting puts direct, sustained pressure on the veins in the pelvic floor and rectal area. If your job or daily routine involves sitting for hours at a time, blood pools more readily in those lower veins. Standing in one place for extended periods has a similar effect, since gravity pulls blood downward and the already-compromised veins struggle to push it back up. Getting up and moving around regularly helps shift weight off the pelvic veins and encourages blood circulation.
Internal vs. External Hemorrhoids
The causes are the same for both types, but the location differs. Internal hemorrhoids form inside the rectum, above the point where the rectal lining transitions to skin. They often cause painless bleeding during bowel movements and may go unnoticed unless they prolapse (push through the anal opening). External hemorrhoids develop under the skin around the anus, where nerve endings are more concentrated. These tend to be more painful, especially if a blood clot forms inside them, creating a firm, tender lump.
During pregnancy, both types can occur. External hemorrhoids are usually more noticeable because of the pain and visible swelling. Internal hemorrhoids may only show up as streaks of bright red blood on toilet paper.
What Helps Reduce the Risk
Since the underlying causes are largely unavoidable parts of pregnancy, management focuses on reducing the factors you can control. A high-fiber diet and plenty of fluids keep stool soft and reduce the need to strain. Fruits, vegetables, whole grains, and legumes all add fiber. Staying within the weight gain range your provider recommends limits the additional pressure on pelvic veins.
Movement matters. Even short, frequent walks throughout the day can improve circulation in the pelvis and prevent blood from pooling. If you sit for work, setting a reminder to stand and move every 30 to 60 minutes makes a difference.
For hemorrhoids that have already appeared, ice packs and witch hazel pads can reduce swelling and ease pain. Soaking in a warm (not hot) bath a few times a day also provides relief. Over-the-counter creams and suppositories are available, though it’s worth checking with your provider about which ones are appropriate during pregnancy. Most hemorrhoids that develop during pregnancy shrink significantly within the weeks after delivery, once the hormonal shifts reverse and the uterus is no longer compressing the pelvic veins.