B. Elnagar et al., IODINE STATUS, THYROID-FUNCTION AND PREGNANCY - STUDY OF SWEDISH AND SUDANESE WOMEN, European journal of clinical nutrition, 52(5), 1998, pp. 351-355
Objective: To examine and compare the effects of pregnancy on the thyr
oid hormone homeostasis in two different populations with variable iod
ine supply. Design: A longitudinal prospective cohort study throughout
pregnancy involving Swedish and Sudanese pregnant women. Setting: The
subjects were enrolled consecutively during their antenatal follow-up
at health centres at Nyby in Uppsala, Sweden and Omdurman in Sudan. S
ubjects: Fifty-one apparently healthy women from Uppsala, Sweden and t
wenty-eight pregnant women from Omdurman, Sudan were recruited during
pregnancy. The mean age and weight of the Swedish women at the beginni
ng of pregnancy were 29.9 +/- 5.4 y and 66.3 +/- 12.9 kg respectively.
The corresponding figures for the Sudanese women were 28.0 +/- 4.9 y
and 64.8 +/- 9.4 kg respectively. Methods: Blood samples were drawn on
four occasions from the Swedish group at 11-13, 24, 32, and 38 weeks
of pregnancy, and on three occasions from the Sudanese group at 10-12,
20-24, and 36-39 weeks. Twenty-four hour urine samples were collected
from the same subjects and on the same occasions as blood sampling. T
he urine samples were kept in a refrigerator until the volumes were me
asured, after which 20 mL aliquots were taken and kept frozen until an
alysed. Main outcome measures: Twenty-four hour urinary iodine output,
TSH, FT4 and T3. Results: The 24 h urinary iodine output at the diffe
rent times during gestation were higher among the Swedish women, with
mean values (95% confidence interval) of 1.40 (1.19-1.61), 1.33 (1.14-
1.51), 1.45 (1.06-1.84) and 1.14 (0.88-1.39) mu mol/d, than among the
Sudanese cohort, with corresponding values of 0.49 (0.27-0.72), 0.29 (
0.19-0.39), 0.56 (0.25-0.88) mu mol/d. No significant changes in daily
urinary iodine loss were observed in the two groups with progression
of pregnancy. However, in the Swedish women the mean free T4 concentra
tion fell from 11.81 pmol/l at the beginning of pregnancy to 8.82 pmol
/l and the mean TSH rose from 1.11-1.95 mU/l between the beginning and
end of pregnancy. Such changes were not detected among the Sudanese w
omen, who had significantly lower mean TSH values than the Swedish wom
en in weeks 36-39 of pregnancy (P < 0.02), and significantly higher FT
4 values than the Swedish women both in weeks 20-24 and in weeks 36-39
(P < 0.005 and P < 0.001) respectively. Conclusions: The study sugges
ts that determination of urinary iodine alone gives inadequate informa
tion about the capacity of an individual to utilize an available iodin
e supply and it also shows the existence of different patterns of thyr
oid response during pregnancy. The history of iodine availability prio
r to and during pregnancy seems to be an important determinant of the
mechanism of thyroid gland response to ensure the extra iodine needed
by the growing fetus. Sponsorship: Financial support for this work was
provided by the Swedish Medical Research Council and InDevelop AB, Up
psala University.