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A longitudinal study of thyroid autoantibodies in pregnancy: the importance of test timing

Ekinci , Elif I., Chiu, W. L., Lu, Zhong X., Sikaris, Ken, Churilov, Leonid, Bittar, Intissar, Lam, Que, Crinis, Nick and Houlihan, Christine A. (2015). A longitudinal study of thyroid autoantibodies in pregnancy: the importance of test timing. Clinical Endocrinology,82(4):604-610.

Document type: Journal Article
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IRMA ID 11381xPUB48
Title A longitudinal study of thyroid autoantibodies in pregnancy: the importance of test timing
Author Ekinci , Elif I.
Chiu, W. L.
Lu, Zhong X.
Sikaris, Ken
Churilov, Leonid
Bittar, Intissar
Lam, Que
Crinis, Nick
Houlihan, Christine A.
Journal Name Clinical Endocrinology
Publication Date 2015
Volume Number 82
Issue Number 4
ISSN 0300-0664   (check CDU catalogue open catalogue search in new window)
Scopus ID 2-s2.0-84924025004
Start Page 604
End Page 610
Total Pages 7
Place of Publication United Kingdom
Publisher Wiley-Blackwell Publishing Ltd.
Field of Research MEDICAL AND HEALTH SCIENCES
HERDC Category C1 - Journal Article (DIISR)
Abstract Objective
Thyroid peroxidase antibodies (TPOAb) and thyroglobulin antibodies (TGAb) are frequently measured to investigate thyroid dysfunction in pregnancy. Despite the recognized fall of these autoantibodies in pregnancy, there is limited guidance on the timing of such testing. We assessed optimal test timing of TPOAb/TGAb for the detection of Hashimoto's thyroiditis and post-partum thyroid dysfunction (PPTD).

Design
Prospective longitudinal study with recruitment in Trimester 1.

Patients
Healthy women ≤13 weeks' gestation from Mercy Hospital for Women, a tertiary obstetric hospital in Melbourne.

Measurements
Serum TPOAb, TGAb, TSH and fT4 were measured at Trimester 1 (T1), Trimester 2(T2), Trimester 3(T3) and postpartum (PP) in each participant. Post-partum thyroid dysfunction (PPTD) was defined if TSH deviated from the assay's nonpregnant reference interval. Longitudinal random-effect logistic regression was used to investigate the association between time and positive/negative thyroid autoantibody status.

Results
Samples from 140 women at T1 (12·0: 10·3–13·0) (median: IQR weeks' gestation); 95 at T2 (24·3: 23·0–25·9), 79 at T3 (35·9: 34·8–36·7) and 83 at PP (12·4: 10·8–14·6 weeks post-partum) were attained. At T1, 13 (9%) and 15 (11%) women had positive TPOAb and TGAb, respectively. The odds of having a positive TPOAb were 96% lower at T2 [OR = 0·04 (95% CI: 0·02–0·8; P = 0·03)] and 97% lower at T3 [OR = 0·03 (95% CI: 0·001–0·6; P = 0·02)] than at T1. Similarly, the odds of having a positive TGAb were 99·4% lower [OR = 0·006 (95% CI: 0–0·3; P = 0·01)] at T2, and 99·5% lower [OR = 0·005 (95% CI: 0–0·4; P = 0·02)] at T3 than at T1. The ROC analysis diagnostic ORs for a positive TPOAb and/or TGAb to predict PPTD were 7·8 (95% CI: 2·2–27·6), 1·2 (95% CI: 0–8·9), 2·0 (95% CI: 0–16·8), and 12·2 (95% CI: 3·3–44·9) at T1, T2, T3 and post-partum, respectively.

Conclusions
A significant proportion of pregnant women lose their thyroid autoantibody positivity after T1. The gestation-dependent loss of TPOAb/TGAb positivity and reduction in diagnostic accuracy for predicting PPTD limits the value of testing at T2 and T3.
DOI http://dx.doi.org/10.1111/cen.12571   (check subscription with CDU E-Gateway service for CDU Staff and Students  check subscription with CDU E-Gateway in new window)
 
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