What causes back pain in a female patient of childbearing age with no past medical history during early pregnancy?

Back Pain in Early Pregnancy

Back pain in early pregnancy is caused by pregnancy hormone-induced ligamentous laxity (primarily relaxin, progesterone, and estrogen) that weakens joint stability, combined with biomechanical changes from increased abdominal mass, postural adaptations, and shifts in the center of gravity that place stress on the spine and supporting structures. 1

Primary Mechanisms

The underlying pathophysiology involves multiple interconnected factors:

• Hormonal ligamentous laxity: Pregnancy hormones cause reduced ligament rigidity throughout the body, particularly affecting the symphysis pubis and sacroiliac joints, which weakens joint stability and increases demand on stabilizing muscles 1, 2

• Biomechanical overload: The growing uterus creates increased abdominal mass that shifts the center of gravity forward, placing additional load on the musculoskeletal system 1

• Postural compensation: As pregnancy progresses, women adopt compensatory postures to accommodate the growing fetus, creating stress on the spine and supporting structures 1

• Muscular insufficiency: Stretched abdominal muscles lose tone and their ability to maintain neutral posture, diminishing their contribution to spinal stability 3

Prevalence and Natural History

Back pain is extremely common during pregnancy:

• Up to two-thirds of pregnancies are affected by low back pain, with prevalence peaking in months 6 and 7 of gestation 1

• Nearly 20% of pregnant women experience pelvic girdle pain involving the anterior and/or posterior aspects of the pelvic ring 1

• Onset timing: While prevalence peaks later in pregnancy, 61% of women report onset during the current pregnancy, with prevalence reaching 48% by the 24th week 4

• Resolution: For most women, back pain resolves spontaneously after delivery 1, 5

Risk Factors to Identify

When evaluating a patient with early pregnancy back pain, specific risk factors predict severity and persistence:

• Pre-pregnancy back pain: Prior history of back pain is a major predictor of pregnancy-related back pain 3, 4

• Multiparity: Increasing parity correlates with higher prevalence, though this is difficult to separate from age effects 3, 6

• Heavy lifting: Lifting 10-20 kg (22-44 lb) more than 20 times per week significantly increases risk 1, 2

• Obesity: Chronic overloading of connective tissue structures from elevated BMI increases musculoskeletal pain risk 1

• Age: Younger women paradoxically report more pain than older women in some studies 4

Clinical Distinction: Lumbar vs. Sacroiliac vs. Round Ligament Pain

Physical examination findings help differentiate pain sources:

• Lumbar pain: Most consistent with discogenic or facet element pain, pronounced on flexion and standing, without neurologic deficit 3

• Sacroiliac pain: Evaluated using posterior pelvic provocation test, ventral/dorsal gapping tests, sacroiliac joint fixation test, Patrick's test (FABERE maneuver), and Derbolowski's test 3

• Round ligament pain: Caused by the same hormonal laxity and biomechanical changes, managed with activity modification and avoiding heavy lifting 2

Red Flags Requiring Urgent Evaluation

Cauda equina symptoms (urinary retention, saddle anesthesia, bilateral leg weakness) represent surgical emergencies even during pregnancy and require urgent MRI evaluation 5

Additional warning signs demanding immediate attention include:

• Persistent excessive shortness of breath
• Severe chest pain
• Regular and painful uterine contractions
• Vaginal bleeding
• Persistent loss of fluid from the vagina
• Persistent dizziness or faintness 2

Common Pitfalls

• Underreporting: Women frequently don't report back pain to prenatal providers, requiring active questioning to identify symptoms 1, 2

• Dismissing early symptoms: While prevalence peaks later, symptoms commonly begin in early pregnancy and increase over time 4

• Inadequate activity modification: Failing to adjust heavy lifting and physical workload worsens symptoms 1, 2

• Overlooking psychosocial impact: Severe musculoskeletal pain associates with sleep disturbances, impaired activities of daily living, elevated depression risk, and delayed resumption of postpartum physical activity 1

Prognosis and Persistent Pain Risk

Women at highest risk for persistent postpartum pain include those with:

• Back pain prior to pregnancy
• Early onset of symptoms during pregnancy
• Higher pain severity during pregnancy
• Both low back pain and pelvic girdle pain simultaneously 1, 2

The incidence of first-onset low back pain postpartum ranges from 19% to 53%, with a mean incidence of 31.6% 7