Endocrine Abstracts

A 37-year-old Asian lady was diagnosed with T3 N1b Papillary carcinoma of the thyroid and operated in 1999. Post operatively she developed hypoparathyroidism and has been on regular calcium and thyroid hormone replacement.

She was on her 5th pregnancy this year. She had 2 previous Caesarian sections and 1 normal vaginal delivery. She was referred to Good Hope Hospital for obstetric care & local tertiary centre for investigation of hypocalcaemia having been troubled with tingling and cramps around 31st week of gestation. Her serum corrected calcium (SCCa) was 1.76 mmol/l with a serum albumin of 37 g/l. She was at this time on Alfacalcidol 2 mcg daily, which was increased to 2.5 mcg daily. A few days later her SCCa revealed that there had been a further drop to 1.50 mmol/l and she was found to have latent tetany and a clearly positive Trousseau sign. She was therefore admitted for intravenous replacement of calcium. Following this her SCCa improved to 2.26 mmol/l. However, SCCa dropped gradually over the next few days to 1.63 mmol/l despite continuing calcium and calcichew replacement. Serum magnesium was normal on magnesium replacement. Renal functions and serum phosphate was unremarkable and serum albumin was 37–39 g/l. Urinary calcium was low at 1.2 mmol/24 h at a time when SCCa was 1.76 mmol/l. She was biochemically euthyroid on thyroxine replacement.

Calcium level was therefore monitored closely between 31st and 35th weeks and she underwent a Caesarian section at 36th weeks of gestation. Interestingly post delivery, SCCa improved to greater than 2.0 mmol/l within two weeks.

Her baby was normocalcaemic at birth. However, the baby was later found to be hypocalcaemic requiring calcium supplementation.

Diagnostic challenges:

1. Why was hypocalcaemia management difficult in this pregnancy?
2. Why was her serum calcium not responding to replacement?
3. Was calcium repeatedly falling due to preferential uptake by the foetus?