USE OF POTASSIUM IODIDE IN PREGNANCY

Potassium iodide (KI) is an inorganic salt used in the management of iodine deficiency and thyroid disorders. Specific indications include the treatment of thyrotoxic crises, as a thyroid protection agent following the release of radioactive-iodine and during MIBG (iodine-131-metaiodobenzylguanidine) scans. Potassium iodide is present in some dietary supplements, including some commercially available prenatal multivitamins. It is also used topically as an antiseptic.

Iodine deficiency or excess can perturb normal fetal thyroid function and development. A joint statement by the World Health Organization (WHO) and the United Nations Children’s Fund (UNICEF) recommends that in situations where iodised salt is unavailable, all pregnant and lactating women should receive iodine supplementation at a dose of 250mcg/day.

Case reports document fetal goitre and abnormal fetal thyroid function, in some instances with persisting postnatal effects, following maternal potassium iodide treatment in pregnancy (at higher doses than used for supplementation). However, the degree to which the underlying maternal disease contributed to fetal outcome in some cases is uncertain.

Data regarding exposure to potassium iodide are limited, and although no association between gestational exposure to potassium iodide and increased risks of miscarriage, congenital malformation, impaired fetal growth, preterm delivery, intrauterine death, or neurodevelopmental delay has been identified, an increased risk cannot be excluded. Limited evidence from a single study on pregnant women with Graves’ disease suggests that risk of miscarriage and congenital malformation may be reduced by switching from methimazole (a teratogen associated with a rare embryopathy) to potassium iodide early in the first trimester. A risk-benefit analysis that takes into account stage of pregnancy and likelihood of maternal disease relapse would, however, need to be undertaken on a case-by-case basis and routine switching is not currently advised.

Where potassium iodide is maternally administered at therapeutic doses, additional fetal and/or neonatal monitoring (e.g., fetal ultrasound, neonatal thyroid function tests) is advised as the presence of a fetal goitre or fetal thyroid dysfunction may impact on delivery and/or the postnatal wellbeing of the neonate. Early discussion with an obstetrician or materno/fetal medicine specialist is recommended for all women on potassium iodide therapy who are pregnant or planning a pregnancy.

Exposure to potassium iodide at any stage of pregnancy would not usually be regarded as medical grounds for termination of pregnancy. However, other risk factors may be present in individual cases which may independently increase the risk of adverse pregnancy outcome. Clinicians are reminded of the importance of consideration of such factors when performing case-specific risk assessments. Discussion with UKTIS is recommended in all cases of therapeutic exposure.