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Hypoparathyroidism, pregnancy and breast feeding
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A woman with hypoparathyroidism and primary hypothyroidism came to see me as a new consult. She was at 32 weeks gestation. As an adolescent, she had a total thyroidectomy for Hashimoto’s thyroiditis which resulted in postoperative hypoparathyroidism. She almost died due to severe hypocalcemia after a miscarriage many years ago. Afterwards, she was told she must never become pregnant again; the risk would be too great. She continued to have frequent episodes of tetany and hypocalcemia which resolved after calcitriol was begun six years ago.
This pregnancy was unexpected but she would like to do everything possible to ensure the health of her baby. She has been managed with once-a-day calcitriol, oral calcium and levothyroxine. I had only limited data regarding previous laboratory results. She did not remember ever collecting a 24-hour urine calcium. However, her most recent thyroid-stimulating hormone level was slightly below nonpregnant normal range; free thyroxine, mid-normal; and total calcium, low-normal.
An obstetrician told her that she must not breastfeed while on calcitriol because of potential harm to the baby. She spoke with a pediatrician who did not think it would be a problem. Her primary care physician recently decreased her dose of levothyroxine because of the slightly low TSH. She subsequently established with a new obstetrician who suggested she see an endocrinologist.
In the past, concerns were raised about the use of calcitriol in pregnancy. High-dose vitamin D was shown to have teratogenic effects in animals. On the other hand, insufficient vitamin D replacement and maternal hypocalcemia can result in miscarriage, neonatal hyperparathyroidism and/or intrauterine fractures.
A PubMed search identified only a handful of case series and review articles on the management of hypoparathyroidism during pregnancy and breastfeeding. Although clinical experience has been limited, there does not appear to be harm due to using calcitriol for the treatment of hypoparathyroidism pregnancy, as long as it is monitored and dosed appropriately. The dose may need to be increased in some patients after the 20th week as physiologic needs increase. After delivery and during lactation, the dose will need to be decreased. Calcium levels and other studies must be monitored closely. There have been reports of severe hypercalcemia in breastfeeding women who did not have calcium levels monitored and dose of calcitriol decreased.
I advised this patient to split her dose and begin taking the calcitriol and calcium twice a day instead of once a day. I disagreed with the recent decrease in the dose of levothyroxine. The nonpregnant normal range for TSH is not what the target during pregnancy should be. A slightly low TSH during pregnancy is not of concern. As long as the free T4 is mid to high normal, the dose of levothyroxine may be continued. After delivery, the levothyroxine can be decreased back to the pre-pregnancy dose (as long as it was optimal). We will be following laboratory studies closely for the duration of her pregnancy and afterwards.
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