Early pregnancy Ref. intervals in TH concentrations in a thyroid antibody-negative pregnant population

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Thyroid.

2011 Jan 22. [Epub ahead of print]

Early

Pregnancy Reference Intervals of Thyroid Hormone Concentrations in a Thyroid

Antibody-Negative Pregnant Population.

Männistö

T, Surcel

HM, Ruokonen

A, Vääräsmäki

M, Pouta

A, Bloigu

A, Järvelin

MR, Hartikainen

AL, Suvanto

E.

1 Department of

Obstetrics and Gynecology, University of Oulu , Oulu, Finland .

Abstract

Background: Thyroid

dysfunction and antibodies are increasingly recognized as risk factors during

pregnancy. Thyroid function changes during pregnancy and there is a need for

gestational age-specific reference intervals for thyroid hormones. The aim of

this study was to calculate gestational age-specific thyrotropin (TSH), free

thyroxine (fT4), and free triiodothyronine (fT3) reference intervals in an

iodine-sufficient thyroid antibody-negative population. Methods: The study

population consisted of a large, prospective population-based cohort, the

Northern Finland Birth Cohort 1986 (singleton births, n = 9362), with extensive data throughout

gestation. The subjects underwent serum sampling in early pregnancy. Samples

were assayed for TSH, fT4, fT3, thyroid-peroxidase, and thyroglobulin

antibodies (n = 5805). All mothers with thyroid

antibodies or previous thyroid diseases were excluded when calculating

gestational age-specific percentile categories for TSH, fT4, and fT3. Also,

associations between body mass index (BMI) and thyroid hormones were

established. Results: The upper reference limit for TSH was 2.5 multiples of

median (2.7-3.5 mU/L, depending on gestational week).

The lower reference limit was as low as 0.07 mU/L.

Reference intervals for fT4 rose during early pregnancy and decreased

thereafter, ranging between 11-22 pmol/L. Reference intervals for fT3 were

uniform throughout gestation, ranging between 3.4 and 7.0 pmol/L. BMI was

associated positively with early pregnancy TSH and fT3 concentrations and

negatively with fT4 concentrations. Conclusions: These gestational age-specific

reference intervals for thyroid hormones provide a framework for clinical

decision making. Overweight and obesity are increasing problems among fertile

women and they are associated with possibility of thyroid dysfunction during

pregnancy.

PMID: 21254924

[PubMed - as supplied by publisher]