ODP492 Longitudinal Prospective Study of Thyroid Function Tests In Pregnancy

Current thyroid function test (TFT) reference ranges in pregnancy are obtained from TPO antibodynegative women in each trimester. Recent international recommendations suggest using specific reference ranges based on local and national population data. Our aim is to study a longitudinal prospective model of TFTs by classifying individuals into groups according to their differing trajectories of TSH and FT4 during pregnancy. We performed a prospective study of TFTs in each trimester in pregnant women attending a national maternity centre. We conducted TFT testing at 12 weeks, between 24-28 weeks and between 34-36 weeks’ gestation. TPO antibody were tested in the second trimester.490 women with no prior history of thyroid disorder have been recruited to date. Mean age was 34+/-5.3. Primiparity was 36.83%. First trimester TSH (median) was 1.44 mmol/L (0.9850-1.90), FT4 14.3 mmol/L (12.90-15.65), second trimester TSH 1.46 mmol/L (1. 09-1.91), FT4 12 mmol/L (10.95-13.15) and third trimester TSH 1.5 mmol/L (1.125-2. 015) and FT4 11.7 mmol/L (10.5-132.2). 20% of women were TPO antibody positive. There were 6 new hypothyroidism diagnoses, all TPO antibody positive and required treatment. Subclinical hypothyroidism was diagnosed in 13 participants with 76.9% TPO antibody positive and 10 requiring treatment. We made 7 new diagnoses of hyperthyroidism, 3 who were antibody positive and requiring treatment. Patients were grouped into three categories based on first trimester TSH: 4 with TSH <0. 05 mmol/L, 409 with TSH 0. 05-2.5 mmol/L and 77 with TSH >2.5 mmol/L. This represents the first longitudinal study of TFTs measured across each trimester of pregnancy in Irish women. 26/490 (5.3%) of women had TFT dysfunction with 19 requiring treatment during pregnancy. One fifth of women had TPO antibody positivity which is a higher proportion than reported in previous studies of thyroid disease in pregnancy. Presentation: No date and time listed