Posterior pelvic discomfort, often described as “butt pain,” is common during pregnancy, particularly in the second and third trimesters. This pain stems from physiological changes that accommodate the growing fetus. A primary driver is the surge of hormones, such as relaxin, which soften connective tissues to prepare the body for childbirth. While necessary, this hormonal shift creates instability and pressure on the musculoskeletal and vascular systems, leading to aches in the lower back, hips, and buttocks.
Nerve Compression: Sciatica and Piriformis Syndrome
Pain presenting as a shooting, burning, or tingling sensation radiating from the lower back or buttocks down the leg is often due to nerve compression. This discomfort is commonly called sciatica, which occurs when the large sciatic nerve is irritated or inflamed. In later pregnancy, the expanding uterus and the baby’s position can exert direct pressure on this nerve where it exits the pelvis, causing the characteristic radiating pain.
A separate cause of sciatic-like pain is Piriformis Syndrome. The piriformis is a small, deep buttock muscle that can tighten or spasm due to postural changes and the increased mechanical load of pregnancy. When this muscle tightens, it can directly compress the sciatic nerve that runs beneath or through it. The altered center of gravity often results in an exaggerated lower back curve (lordosis), which puts constant strain on the piriformis muscle, making this muscle-based compression a frequent cause of posterior pain.
Joint Instability: Pelvic Girdle Pain
Joint instability, collectively known as Pelvic Girdle Pain (PGP), is another major source of buttock discomfort. PGP encompasses pain in the sacroiliac (SI) joints at the back of the pelvis and the pubic symphysis at the front. The SI joints are typically very stable, but hormones like relaxin cause supporting ligaments to soften and stretch.
This ligament laxity allows the pelvis to widen but can lead to uneven movement or misalignment of the SI joints. This is often felt as a deep, dull ache on one or both sides of the posterior pelvis. Pain is frequently triggered by asymmetrical movements, such as turning over in bed, walking, climbing stairs, or getting in and out of a car. The altered biomechanics and increased weight load combine with the joint laxity to reduce the stability of the pelvic girdle.
Vascular and Digestive Causes
Some buttock pain is vascular or digestive, often localized to the anal or rectal area. Hemorrhoids are a common cause of this localized pain, presenting as swollen, enlarged veins in the anus or lower rectum. The expanding uterus puts extra pressure on the inferior vena cava, a major vein that drains the lower body, which increases pressure in the rectal veins and leads to swelling.
This vascular swelling causes sharp, throbbing, or aching pain, often accompanied by itching or bleeding. Severe constipation is a common side effect of pregnancy hormones and iron supplements. Constipation significantly contributes to hemorrhoid formation by increasing straining during bowel movements. Pressure from the enlarged uterus can also compress the colon, further exacerbating constipation and resulting anal/rectal pain.
Managing Pain and Seeking Relief
Relief for pregnancy-related butt pain often begins with postural adjustments that minimize stress on the pelvis and nerves. These simple changes, combined with targeted support, can significantly alleviate discomfort caused by joint instability or nerve compression.
- When sitting, avoid crossing your legs and ensure your feet are flat on the floor.
- For extended sitting, take frequent short breaks to stand and walk.
- During sleep, lie on your side with a pillow placed between your knees and another supporting your belly to promote better spinal alignment and reduce pressure on the sciatic nerve.
- Wearing a maternity support belt, sometimes called a belly band, can provide gentle compression and support to unstable pelvic joints, which is particularly helpful for Pelvic Girdle Pain.
- Gentle movement and stretching, such as incorporating pelvic tilts or a modified figure-four stretch, help release tension in the piriformis muscle.
- For pain localized to the rectum from hemorrhoids, soaking in a warm sitz bath or applying witch hazel pads can soothe the inflamed area.
It is recommended to consult with a physical therapist specializing in prenatal care for a personalized program of strengthening and movement based on the specific cause of your pain. Seek immediate medical attention if you experience severe, sudden-onset pain, pain accompanied by fever, or if you suddenly lose the ability to walk or control your bladder or bowels. Tailored interventions can lead to significant relief.