Incorporating thyroid markers in Down syndrome screening protocols

Antenatal screening for thyroid dysfunction: pre-term birth, low birth-weight, and growth restriction

OBJECTIVE

To assess pre-term birth, low birth-weight and growth restriction according to maternal thyroid screening results and subsequent treatment.

METHODS

This is a nonintervention nested case-control study derived from 10,052 asymptomatic women previously screened during the first trimester marker with anti-thyroid peroxidase antibodies, serum thyroid stimulating hormone, and free thyroxine. Screening results had been classified as positive with one or more markers outside the normal range and referred to an endocrinologist. Cases were 512 women with positive results and information on recommended treatment: 204 thyroxine, propylthiouracil or surgery, and 308 no treatment or only iodine. Controls were a sequential sample of 1292 women with negative results. All cases and controls had information on gestation at delivery or birth-weight. Outcome measures were pre-term birth (<37 weeks), low birth-weight (<2.5 kg) and, for singletons, small for gestational age (SGA; <10th percentile).

RESULTS

Among singleton pregnancies, there was a higher prevalence of both pre-term birth (risk ratio (RR) 1.69, 95% confidence interval (CI) 1.21-2.36, p < .002) and low birth-weight (RR 1.72, 95% CI 1.13-2.62, p < .02) in cases compared with controls. An increase in low birth-weight was also present in term pregnancies, but not significant (RR 1.80, 95% CI 0.78-4.14, p = .16), and there was no difference in SGA prevalence (1.24, 95% CI 0.93-1.65, p = .14). Among cases there was no significant difference in these rates according to treatment even after logistic regression, allowing for the individual screening marker levels and maternal weight.

CONCLUSIONS

Women with positive thyroid screening results are at increased risk of pre-term birth regardless of thyroid dysfunction or subsequent treatment. An association with low birth-weight is probably secondary to early delivery.

Maternal thyroid-stimulating hormone reference ranges for first trimester screening from 11 to 14 weeks of gestation

BACKGROUND

To establish maternal thyroid-stimulating hormone (TSH) reference ranges for first trimester screening from 11 + 0 to 13 + 6 weeks of gestation.

METHODS

A total of 10 592 singleton and 201 twin consecutive Caucasian pregnant women who underwent simultaneously prenatal first trimester Down's syndrome screening and thyroid function screening from January 2010 to November 2017 were included in the study. Women with positive antithyroid peroxidase antibody (TPOAb) and positive personal history of thyroid disease were previously excluded. TSH was measured by immunochemiluminescent assay on ci 16200 Abbott Architect analyzer. Nonparametric percentile method (also known as CLSI C28.A3) was used for the determination of reference ranges.

RESULTS

We established reference ranges of TSH for the period of gestation from 11 + 0 to 13 + 6 weeks of pregnancy as 0.16-3.43 mU/L for singleton Caucasian pregnancies and 0.02-2.95 mU/L for twin Caucasian pregnancies. The median (IQR) of TSH for singleton pregnancies was higher than that for twin pregnancies (1.25 mU/L (0.83-1.81) vs 0.84 (0.37-1.47), respectively; P < .0001).

CONCLUSIONS

Each first trimester screening center should be aware of which type of immunoassay their laboratory uses. TSH reference ranges in women during the first trimester of pregnancy are lower than those for general population. Twin pregnancies have lower TSH than singleton pregnancies.