Endocrine Abstracts

Background: Recent evidence suggests that detection of fetal goitre (defined as fetal thyroid circumference >95th percentile) may be a useful way of detecting over and under activity of the fetal thyroid in maternal Graves’ disease. Clinical translation is made difficult by the large differences in normative data from different populations. We examined fetal thyroid circumference in our population against normative data based on at least 150 examinations. Normative data from the US, France and Israel were included.

Methods: Fetal thyroid was examined using transabdominal ultrasound (Siemens Acuson Antares, 3.5 MHz curvilinear transducer) in 60 normal women with no history of thyroid disease at 20 to 36 weeks of gestation (mean±S.D.: 28.3±5.8 weeks). Data were expressed a) as proportion between 5th and 95th percentile (US, France) or 2.5th–97.5th percentile (Israel) for each set of normative data and b) as the difference from the mean thyroid circumference by week of gestation for each set of normative data (available for US and Israel only).

Results: Fetal thyroid circumference was most similar to US and French normative data. Mean thyroid circumference showed a small but significant 8% increase over the US average (mean±S.E.M.: +2.6±0.6 mm, P<0.01). Thyroid circumference was above the US 95th percentile in 4 cases (7%) and above the French 95th percentile in 2 cases (3%). By contrast our data appeared quite different to Israeli data: mean thyroid circumference was 24% below the Israeli mean (−12.0±0.6 mm; P<0.01), with no cases above the 97.5th percentile and the majority of cases below the 2.5th percentile (55 cases, 92%).

Conclusions: Normative data for fetal thyroid measurements differ between populations. It is not clear whether this represents true differences between populations or technical artefact. Clinical detection of fetal goitre requires identification of appropriate normative data for the local population.