Thyroid volume by ultrasound in asymptomatic gravid and non-gravid controls in a negroid population in Nigeria

Abstract

Background: The thyroid gland is among the most commonly imaged glands using ultrasound due to the limitation of clinical examination. During pregnancy, thyroid volume responds physiological to the increased demands for iodine and energy. An enlargement of the thyroid gland during gestation is, therefore, not abnormal. However, this may be confused for goiter, which the World Health Organization (WHO) and the International Council for the Control of Iodine Deficiency Disorders have recommended to be investigated through ultrasound.

Objective: To establish a local reference volume of the thyroid gland in asymptomatic pregnant women that could be used to define goiter in the context of iodine deficiency disease monitoring.

People and Methods: A total of 430 volunteers made up of 399 pregnant women and 31 nonpregnant female control were recruited prospectively and purposively. After obstetrics scan with a 3.5 MHz curvilinear transducer, the subject’s thyroid gland was subsequently scanned with a 7.5 MHz linear transducer. The cranio‑caudal, antero‑posterior, and transverse diameter of each lobe represented the length, height, and width, respectively. These were subsequently multiplied with a WHO‑recommended correction factor (0.479) to derive the volume. A summation of the volumes of both lobes gave the total thyroid volume for each subject.

Results: The mean thyroid volumes (±standard deviations) in pregnant women and nonpregnant controls were 8.26 ± 4.17 cm³ and 2.54 ± 0.46 cm³, respectively. The mean for the first to third trimesters were 5.17 ± 1.83 cm³, 7.81 ± 2.44 cm³, and 11.81 ± 4.53 cm³, respectively. A one‑way analysis of variance showed significant differences in the mean thyroid volumes within the three trimesters (P = 0.000).

Conclusion: The wide variation in thyroid volume between pregnant women and nonpregnant controls points to the possibility of deficient dietary iodine intake during gestation in our locality. Special attention on daily minimum iodine intake for gravid women as recommended in other countries is advised.

Keywords: Pregnant women, thyroid, ultrasound, volume