What are the differential diagnoses for a pregnant woman who feels like her hips are pulling apart?

Differential Diagnoses for Hip "Pulling Apart" Sensation in Pregnancy

The sensation of hips pulling apart during pregnancy is most commonly caused by symphysis pubis dysfunction (SPD) or pelvic girdle pain (PGP), which affects nearly 20% of pregnant women and results from pregnancy hormone-induced ligamentous laxity combined with biomechanical stress on the pelvic ring. 1, 2

Primary Differential Diagnoses

1. Symphysis Pubis Dysfunction (SPD) / Pelvic Girdle Pain (PGP)

• Most likely diagnosis for the "pulling apart" sensation, affecting the anterior and/or posterior aspects of the pelvic ring 1
• Caused by pregnancy hormones (relaxin, progesterone, estrogen) that soften and relax the symphysis pubis and sacroiliac joints, allowing the rigid bony pelvis to expand 1, 2
• Pain typically worsens with weight-bearing activities, walking, climbing stairs, and turning in bed 3
• Peaks in months 6-7 of gestation 1, 2
• Diagnosed by reproducing pain with sacroiliac provocation tests and symphyseal palpation 3

2. Sacroiliac Joint Dysfunction

• Results from the same hormonal laxity affecting the posterior pelvic ring 1
• Pain localized to one or both sacroiliac joints, often described as deep buttock or posterior hip pain 3
• Exacerbated by unilateral weight-bearing, prolonged standing, or transitional movements 2

3. Pregnancy-Related Stress/Insufficiency Fractures

• Critical not to miss: Rare but serious cause of pelvic pain in pregnancy 4
• Most commonly affects the sacrum, femoral neck, or pubic rami 4
• Risk factors include: vaginal delivery of high-birth-weight infant, excessive weight gain, rapid vaginal delivery, pregnancy-related osteoporosis 4
• Presents with intractable lower back or pelvic pain, loss of mobility, and symptom exacerbation with weight-bearing 4
• Red flag: Pain that is severe, unremitting, or prevents weight-bearing requires imaging evaluation 4

4. Round Ligament Pain

• Caused by stretching of the round ligaments supporting the uterus 2
• Typically sharp, stabbing pain in the lower abdomen or groin, often unilateral 2
• Triggered by sudden movements, coughing, or position changes 2
• Less likely to cause the specific "pulling apart" sensation at the hips

5. Meralgia Paresthetica

• Entrapment of the lateral femoral cutaneous nerve as it passes around the anterior superior iliac spine or through the inguinal ligament 5
• Presents with numbness, burning, or tingling on the anterolateral thigh rather than true hip pain 5
• Can occur at any time during pregnancy or immediately postpartum 5
• Distinguished by sensory symptoms rather than mechanical pain

6. Hip Algodystrophy (Transient Osteoporosis of Pregnancy)

• Rare cause of hip pain in pregnancy, typically third trimester 6
• Presents with inguino-crural pain and functional impotence 6
• More likely to cause unilateral hip pain rather than bilateral "pulling apart" sensation 6

Key Distinguishing Features

Clinical Examination Findings

• SPD/PGP: Pain with palpation over symphysis pubis, positive sacroiliac provocation tests, waddling gait, difficulty with single-leg standing 3, 7
• Stress fracture: Severe, focal tenderness over affected bone, inability to bear weight, pain at rest 4
• Meralgia paresthetica: Sensory changes on anterolateral thigh, no mechanical hip pain 5

Timing and Progression

• SPD/PGP: Usually begins in first trimester, worsens with advancing pregnancy and subsequent pregnancies 7
• Stress fracture: Typically last trimester or immediately postpartum 4
• Most conditions: Resolve spontaneously after delivery, though 26.5% may have persistent symptoms at 4 months postpartum 3

Red Flags Requiring Urgent Evaluation

Immediate imaging (MRI preferred in pregnancy) is indicated for: 4, 2, 8

• Cauda equina symptoms: urinary retention, saddle anesthesia, bilateral leg weakness
• Severe pain preventing weight-bearing or ambulation
• Pain unresponsive to conservative measures with progressive functional decline
• Suspicion of fracture based on severe focal tenderness

Diagnostic Approach

Initial Evaluation

• Clinical examination: Palpate symphysis pubis, perform sacroiliac provocation tests, assess gait pattern 3
• Risk factor assessment: Previous pelvic pain, family history, heavy lifting (>10-20 kg more than 20 times weekly), obesity 1, 2
• Radiographs: Generally avoided in pregnancy unless fracture suspected and diagnosis will change management 4

Advanced Imaging (When Indicated)

• MRI without contrast: Preferred modality in pregnancy for suspected stress fracture or when diagnosis unclear 4
• Ultrasound: Limited utility for pelvic bone pathology but no radiation exposure 4
• Radiographs: Fetal absorbed dose from pelvis radiograph is 1.1 mGy (well below 50 mGy safety threshold), acceptable when fracture suspected 4

Common Pitfalls to Avoid

• Underdiagnosis: Women often don't report pelvic pain to prenatal providers; active questioning is essential 1, 2
• Dismissing severe symptoms: Assuming all pelvic pain is "normal" pregnancy discomfort can delay diagnosis of stress fractures 4
• Inadequate activity modification: Failing to counsel on avoiding heavy lifting worsens symptoms 1, 2
• Missing family history: Strong genetic component to pelvic joint syndrome and developmental dysplasia of the hip in offspring (45/1,000 vs 9/1,000 general population) 7