The cause of back pain in pregnancy is often considered multifactorial, meaning several factors act concomitantly on various structures in the lower body, causing pain. These factors are commonly recognized as the anatomical, postural, vascular, and hormonal changes that take place naturally during the course of pregnancy.
While most of these changes are considered normal, rarely, a few causes of lower back pain in pregnancy may indicate serious conditions, some of which may even be life-threatening.
Musculoskeletal Causes of Pregnancy Back Pain
During pregnancy, new changes in the mechanics of the lower back may occur, and many existing conditions may become worse, adding to the discomfort.
New changes in posture and stability of the lower back
The instability of the pelvis and lower back occurs due to the increase in the size of the uterus. These changes cause the spine to alter its shape, making the lower back more curved than usual. Muscles that stabilize the pelvis, such as the psoas, are shortened, further increasing the curvature of the lower back and causing pain.1
Laxity of soft tissues and joints
The concentration of the relaxin hormone rises considerably during pregnancy, which increases tissue and joint flexibility in the lower back. The sacroiliac joints may become increasingly lax under the influence of this hormone. Since the sacroiliac joints are responsible for maintaining pelvic stability and transferring loads from the spine to the legs, the loosening of these joints may add to postural problems and increase the risk of back pain.1
Widening of the pelvis
The concentration of the estrogen hormone also increases during pregnancy. The combined effects of relaxin and estrogen cause the pelvis to widen. This widening begins during the 10th to 12th week of pregnancy and causes the pelvis to increase in width by 10 mm or less. Pelvic pain typically becomes more in the later stages of pregnancy and may rapidly progress, causing severe pain in the lower back and thighs. The muscles and soft tissues in the area are often affected, causing pain while walking and resulting in an altered gait.1
Neural Causes of Pain During Pregnancy
The peripheral nerves, such as the lateral femoral cutaneous nerve, in the pelvis and thigh region may become compressed, stretched, or lose blood supply, making them the primary source of pain. Swelling of the soft tissue may cause additional mechanical pressure on these nerves, causing thigh pain and referred pain in the lower back and pelvis.
Concomitant medical conditions, such as obesity, diabetes, and anatomical variations increase the risk of peripheral nerve pain in the legs.
Herniated Disc Pain in Pregnancy
Rarely, the increased stress and strain on the lower skeletal system and musculature may affect the spinal discs, resulting in herniation.2,3 A herniated lumbar disc may affect the nearby nerve roots causing sciatica symptoms to travel down the thigh and leg, and possibly into the foot. The medical term for sciatica is radiculopathy and typically affects one side of the body.
It is also possible that previous sciatica may become aggravated during pregnancy.1
Read more about Lumbar Radiculopathy
Weakening of the Hip Bone and Joint
Rarely, some women may develop a bone-weakening condition called osteoporosis in the third trimester of pregnancy. The exact cause of this condition is unknown. The symptoms may appear slowly or suddenly, affecting the tissues of the hip joint, causing pain and limited hip motion. While the symptoms may be typical, this condition is diagnosed by medical imaging tests, such as an x-ray, MRI, and/or pelvic sonogram.1
Another condition that affects the hip region, avascular necrosis of the femoral head, may occur due to biological changes in pregnancy. These changes typically include weight gain and production of high levels of natural steroids, which may cause destruction of bone tissue in the femoral head (top part of the thigh bone), resulting in groin and lower back pain.1
Placental Location and Back Pain
A posterior (back) location of the placenta (the tissue that provides nourishment to the fetus) is known to cause back pain in some pregnant women. In these cases, the placenta is located near the posterior wall of the uterus.1
Limited research indicates that a posterior placenta may also cause poor pregnancy outcomes and preterm labor.4
Ruptured Ectopic Pregnancy
Severe lower back and groin pain may occur when the fallopian tube ruptures due to an ectopic pregnancy.5 This condition is a medical emergency and occurs in early pregnancy, typically within the first few weeks or first trimester.
Infection and Back Pain
Urinary tract infections and kidney infection (pyelonephritis) may cause lower back pain. The pain is typically characterized as a dull and persistent ache accompanied by fever and/or chills. These conditions may carry a risk of preterm labor in some women.1
Obstetrical Conditions that May Cause Back Pain
While not common, certain obstetrical conditions, such as spontaneous abortion, ovarian cysts, pelvic or uterine adhesions, fibroids, or collection of fluid, may cause lower back pain in pregnancy.
Back pain may also result as a sign of labor (full-term or pre-term) and is typically associated with uterine contractions that gradually increase in intensity.
Daily Activities that May Cause Back Pain
In addition to the conditions listed above, a few other factors can cause pain in the lower back or posterior pelvis. These factors typically include activities that create asymmetrical loading of the spine, pelvis, and hips. Common activities that load the spine in an uneven form include:
- Walking and/or running
- Rolling over in bed
- Bending forward
- Twisting the spine
- Lifting objects off the floor
- Navigating stairs
Back pain is common in pregnancy and typically resolves after delivery, but several conditions causing this symptom require medical attention to prevent future complications. Seeking medical care for pregnancy-related back pain is advisable. A physician can accurately diagnose the cause of back pain and provide the needed care for treating the symptoms.