Endocrine Abstracts (2007) 13 P320

Thyroid function testing in hypothyroid women during pregnancy

Biju Jose, Khaled Ashawesh, Chris Ayres, David Redford & David Barton


Princess Royal Hospital, Telford, United Kingdom.


Background: Maintenance of euthyroidism is particularly important during pregnancy. In the early stages of gestation, maternal thyroid hormone is required for foetal neurological development. Some authors suggest presumptively increasing the thyroxine replacement at diagnosis of pregnancy. Recent United Kingdom guidelines recommended that thyroid stimulating hormone (TSH) and free T4 (fT4) should be measured in hypothyroid women before conception, at diagnosis of pregnancy, at antenatal booking, once in the second and third trimesters and after delivery.

Aim: To evaluate existing practice of thyroid function tests in hypothyroid women in a combined endocrine antenatal clinic, in light of new recommendations from Association of Clinical Biochemists and British Thyroid Association.

Methods: 24 women with primary hypothyroidism delivered between January 2005 and July 2006. Retrospective analysis identified those who had TSH and fT4 performed and when.

Results: Of 24 patients, 16 (67%) had TSH assay at preconception visit, 20 (83%) at antenatal booking, 21 (88%) in 2nd trimester, 23 (96%) in 3rd trimester, while only 6 (25%) had TSH performed post-partum. FT4 assays were performed in 3 (12%) women at pre-conception visit, 10 (42%) at antenatal visit, 4 (17%) in 2nd trimester, 2 (8%) in 3rd trimester and 2 (8%) in post partum period.

Comments: These data indicate satisfactory practice in performing TSH assays at antenatal booking and in the subsequent trimesters. Inadequacies were apparent, especially, the need to improve the use of preconception and post-partum TSH assays. A formal arrangement to perform TSH assay at diagnosis of pregnancy needs consideration. Our practice should adapt to new recommendations to include fT4 in the care of hypothyroid women during pregnancy. TSH alone can be misleading due to the hormonal dynamics during early pregnancy.

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