Routine First Trimester Screening for Maternal Thyroid Disease

Abstract

The aim was to assess the proportion of women requiring a referral to an endocrinologist when carrying out routine screening for maternal thyroid disease simultaneously with screening for Down syndrome. Between November 2009 and September 2015, women having a first trimester combined test were screened; those symptomatic or being investigated for thyroid problems were excluded. In the first half of the period the blood sample was tested for anti-thyroid peroxidase (TPO) antibodies, serum thyroid stimulating hormone (TSH), and free thyroxine (fT4); thereafter fT4 was not used. Women with at least one analyte outside the range (TPO more than 5.6 kU/L, TSH 0.35–4.94 mU/L, fT4 9.0–19.1 pmL/L) were referred to an endocrinologist for counseling. Of 10,052 women screened, 1190 (11.8%) had TSH, fT4, or antibody levels outside the range; 13.0% when fT4 was used and 10.4% thereafter. Most of these positive results were due to a single abnormal marker. There was a much higher positive rate in multiple pregnancies (27.3% compared with 11.5% in singletons; P < 0.0001). There was an association between positivity and maternal age ( P < 0.0001), a higher rate in the small ethnic group of Asians ( P < 0.0005) and a lower rate among smokers ( P < 0.02) and following assisted reproduction ( P < 0.05). Routine antibody and hormone testing at the same time as the combined test generated a large number of referrals but this did not overload the services.

Incorporating thyroid markers in Down syndrome screening protocols

“…The Down syndrome mean for TSH was the weighted average in the two published studies – 0.80 multiple of the normal median (MoM); the mean for fT4 was assumed to be 1.00 MoM. The correlation coefficients for TSH and fT4 were derived from a series of women screened in our centre for both thyroid disease and had a simultaneous combined test . These values were assumed to be the same for affected and unaffected pregnancies.…”

“…Levels were expressed in MoMs: PAPP‐A and free β ‐hCG using local gestation‐specific equations, NT using a published crown rump length (CRL)‐specific equation and TSH and fT4 using equations derived from the data. Seven potential co‐variables were assessed in TSH and fT4 MoM calculations: CRL, maternal weight, maternal age, ethnicity, smoking status, parity and assisted reproduction . Gaussian fit required logarithmic transformation of MoMs except for TSH, which was transformed using the square root .…”

“…Seven potential co-variables were assessed in TSH and fT4 MoM calculations: CRL, maternal weight, maternal age, ethnicity, smoking status, parity and assisted reproduction. 9,14,16 Gaussian fit required logarithmic transformation of MoMs except for TSH, which was transformed using the square root. 16 Standard deviations were derived from the 10th to 90th centile difference divided by 2.563 after transformation, where applicable.…”

Women with Positive First Trimester Thyroid Disease Screening Results

“…These considerations prompted the Fetal Medicine Centre in the Department of Obstetrics and Gynaecologists, Zlin, Czech Republic-an iodine sufficient country-to promote routine antenatal screening using thyroid antibodies and hormones [5]. Between November 2009 and September 2015, women having a first trimester Down's syndrome screening test were simultaneously screened for thyroid disease.…”