Condition category
Nutritional, Metabolic, Endocrine
Date applied
Date assigned
Last edited
Retrospectively registered
Overall trial status
Recruitment status
No longer recruiting
Publication status

Plain English Summary

Background and study aims.
There is evidence from previous studies that low thyroid function during pregnancy may affect the intelligence quotient (IQ) of the child. However there have been no prospective studies to confirm this. We carried out a study to answer the question: Does testing thyroid function in early pregnancy and treating those women with underactive thyroids improve the IQ of their children?

Who can participate?
We recruited 22000 women pregnant with one baby (singleton pregnancies) before 16 weeks gestation who were not taking thyroid medication.

What does the study involve?
Blood samples were randomly allocated to a screen group and a control group. Thyroid testing was done immediately in all samples from the screen group. The control group samples were stored until the woman delivered the baby and the thyroid test was then carried out. Note: at the time of this trial (2002) there was no routine screening of thyroid function in pregnant women. The screen group women who were found to have an underactive thyroid received Levothyroxine daily for the length of the pregnancy. The control group received no treatment during pregnancy. The women who had an underactive thyroid diagnosed after delivery were referred to their general practitioner for standard care.

What are the possible benefits and risks of participating?
The women participating had a 50% chance of having thyroid function measured during early pregnancy (compared to 0% chance in normal practice). They then had the opportunity to see if the thyroxine intervention improved the IQ of their child compared to the children born to mothers from the control group. Side effects of thyroxine include palpitations and tiredness. Thyroid testing was done in women taking thyroxine 6 weeks after starting and again at 30 weeks of pregnancy. Less than 5% of women required a dose adjustment.

Where is the study run from?
The study was run from the University Hospital of Wales, Cardiff University. There were approximately 8 centres including one in Turin, Italy.

When is the study starting and how long is it expected to run for?
The study started in 2002 and ended in 2010.

Who is funding the study?
Wellcome Trust

Who is the main contact?
Professor JH Lazarus

Trial website

Contact information



Primary contact

Prof John H Lazarus


Contact details

Cardiff University
University Hospital of Wales
Professor of Clinical Endocrinology/
Heath Park
CF14 4XN
United Kingdom
+44 (0)29 20 742193

Additional identifiers

EudraCT number number

Protocol/serial number


Study information

Scientific title

Randomised controlled trial of the effect of gestational thyroid hormone intervention therapy on childhood development



Study hypothesis

Aim is to evaluate strategy of screening of thyroid function in early pregnancy.

Ethics approval

Trent Multi-Centre Research Ethics Committee, 24/06/2004, ref: MREC/04/4/026

Study design

Multicentre randomised controlled trial

Primary study design


Secondary study design

Randomised controlled trial

Trial setting


Trial type


Patient information sheet

Not available in web format, please use the contact details below to request a patient information sheet


Childhood development


Sera obtained from pregnant women before 16 weeks gestation. Sera randomised to 'screen' (T4 and Thyroid Stimulating Hormones [TSH] measured at time of randomisation) and 'control' (hormones measured post delivery) groups. Thyroxine intervention given to screen group with low T4/high TSH and to control group postpartum.
This is the only prospective randomised intervention trial of thyroxine in early pregnancy.

Intervention type



Not Applicable

Drug names

Primary outcome measure

Intelligence Quotient (IQ) of children in screen and control groups.

Secondary outcome measures

No secondary outcome measures

Overall trial start date


Overall trial end date


Reason abandoned (if study stopped)


Participant inclusion criteria

All pregnant women (aged 18 - 45 years) before 16 weeks gestation

Participant type


Age group




Target number of participants


Participant exclusion criteria

1. Twin pregnancy
2. Thyroid treatment (T4 or antithyroid drugs)

Recruitment start date


Recruitment end date



Countries of recruitment

United Kingdom

Trial participating centre

Cardiff University
CF14 4XN
United Kingdom

Sponsor information


Cardiff University (UK)

Sponsor details

McKenzie House
Physical and Financial Resources
30-36 Newport Road
PO Box 497
CF10 3XR
United Kingdom
+44 (0)29 2087 9255

Sponsor type




Funder type


Funder name

Wellcome Trust (UK) (grant ref: GRO65143MA)

Alternative name(s)

Funding Body Type

private sector organisation

Funding Body Subtype

International organizations


United Kingdom

Results and Publications

Publication and dissemination plan

Not provided at time of registration

Intention to publish date

Participant level data

Not provided at time of registration

Basic results (scientific)

Publication list

2012 results in:

Publication citations

  1. Results

    Lazarus JH, Bestwick JP, Channon S, Paradice R, Maina A, Rees R, Chiusano E, John R, Guaraldo V, George LM, Perona M, Dall'Amico D, Parkes AB, Joomun M, Wald NJ, Antenatal thyroid screening and childhood cognitive function., N. Engl. J. Med., 2012, 366, 6, 493-501, doi: 10.1056/NEJMoa1106104.

Additional files

Editorial Notes