Osteomalacia in Pregnancy

Definition

• Fetal skeletal development draws heavily on maternal calcium and vitamin D stores
• Nutritional intake may be inadequate
• Limited sunlight exposure worsens the deficit

"In adults, vitamin D deficiency may result in osteomalacia which occurs mainly in women, especially during pregnancy and lactation when requirements of vitamin D are increased."

• Park's Textbook of Preventive and Social Medicine

Causes

Primary Cause: Vitamin D Deficiency

1. In the liver → 25-hydroxyvitamin D (25-OHD) - the storage form
2. In the kidney → 1,25-dihydroxyvitamin D (calcitriol) - the active form

Causes Classified by Mechanism

Signs and Symptoms

Symptoms

• Bone pain - generalized, poorly localized; worse in pelvis, spine, ribs, lower extremities; worse at night and with weight bearing
• Proximal muscle weakness - difficulty climbing stairs, rising from a chair/toilet; patients pull themselves up by hand rails
• Waddling gait - flat-footed, springless "mother penguin's walk" due to combined bone pain and muscle weakness
• Muscle cramps, paresthesias - fingertip tingling from hypocalcemia

Signs on Examination

• Bone tenderness - elicited by pressing on the tibiae, wrists, pubic rami, iliac crests, or rib cage compression
• Chvostek's sign - facial twitch with gentle tap anterior to the ear (hypocalcemia)
• Trousseau's sign - carpopedal spasm with blood pressure cuff inflation (hypocalcemia)
• Pelvic deformity - the pelvis may become narrowed/contracted (triradiate or flat-rachitic pelvis), creating contracted pelvis - a major obstetric concern
• Kyphoscoliosis, scoliosis in severe long-standing cases
• Wrist enlargement, rickety rosary in coexisting rickets/severe deficiency

Specific Obstetric Concern

Investigations / Diagnosis

Biochemistry

Radiology

• Looser's zones (pseudofractures) - pathognomonic: narrow lucent bands perpendicular to the bone cortex, often bilateral and symmetric, seen at the femoral neck, pubic rami, ribs, and scapulae
• Generalized bone rarefaction / osteopenia
• Pelvic deformity on X-ray: triradiate pelvis, platypelloid shape
• Bone scan may show focal uptake that can be mistaken for metastatic disease

Pseudofracture of the femoral neck - a hallmark radiographic finding in osteomalacia (Goldman-Cecil Medicine)

Bone Biopsy (rarely needed in pregnancy)

• Tetracycline double-labeling showing excess unmineralized osteoid - gold standard but impractical in pregnancy

Management as a High-Risk Pregnancy

1. Contracted pelvis → CPD → obstructed/prolonged labor → risk of uterine rupture, fetal distress
2. Hypocalcemia → maternal tetany, seizures, cardiac arrhythmia; neonatal hypocalcemia and congenital rickets
3. Maternal bone fragility → pathological fractures (pelvis, vertebrae, femoral neck) during labor
4. Neonatal consequences → neonatal hypocalcemia, neonatal seizures, congenital rickets, low birth weight, fractures in the newborn

Antenatal Management

1. Early Identification

• Detailed history: diet, sunlight exposure, veiling practices, previous pregnancies with similar symptoms, malabsorption disorders
• Book as high-risk; refer to a tertiary center with multidisciplinary team (obstetrician, endocrinologist, neonatologist)
• Baseline blood work: serum calcium, phosphate, alkaline phosphatase, 25-OHD, PTH, renal and liver function tests

2. Vitamin D Supplementation

• The goal is to raise 25-OHD to > 30 ng/mL and normalize PTH
• Calcitriol is preferred in malabsorption because it bypasses the need for hepatic and renal hydroxylation
• Monitor serum calcium every 2-3 weeks once treatment starts
• Urinary Ca:Cr ratio should remain < 0.22 (mg/mg)
• Caution: excess vitamin D in pregnancy can cause fetal/neonatal hypercalcemia; do not exceed safe doses

3. Calcium Supplementation

• 1,000-1,500 mg/day of elemental calcium in divided doses (3x/day with meals for best absorption)
• Calcium citrate is preferred over carbonate in malabsorptive conditions
• Monitor urinary calcium to avoid hypercalciuria/nephrolithiasis

4. Nutrition and Lifestyle

• High-calcium diet: dairy products, green leafy vegetables, fortified foods
• Safe sunlight exposure: 15-30 minutes/day to face and arms
• Treat underlying cause: gluten-free diet for celiac, manage liver/renal disease
• Correct hypomagnesemia if present (critical for PTH secretion)

5. Pelvic Assessment

• Clinical pelvic assessment and pelvimetry (X-ray pelvimetry is avoided in pregnancy; MRI pelvimetry preferred)
• Serial obstetric ultrasounds for fetal growth and biometry
• Document pelvic dimensions for delivery planning

Intrapartum Management

• Mode of delivery is the most critical decision:
  • If pelvis is adequate and no deformity: allow trial of labor with close monitoring
  • If pelvis is contracted (CPD) or deformed: elective Caesarean section is indicated to prevent obstructed labor, uterine rupture, and fetal demise
• Regional anesthesia (epidural/spinal) is generally safe; document vertebral deformities pre-procedure
• Monitor for hypocalcemic tetany during labor (calcium gluconate IV must be available)
• Calcium gluconate 10% (10 mL IV slowly) for acute hypocalcemic tetany or Chvostek-positive symptomatic patients during labor

Postpartum / Neonatal Management

• Continue vitamin D and calcium supplementation during lactation (requirements remain high)
• Breastfed infants of deficient mothers need vitamin D 400 IU/day supplementation
• Check neonatal serum calcium in the first 24-72 hours - neonatal hypocalcemia may manifest as jitteriness, apnea, or seizures
• Assess newborn for congenital rickets (bony deformities, soft skull/craniotabes)
• Arrange bone mineral density assessment for the mother postpartum

Summary Table