Asia Pacific J Clin Nutr (1993) 2, 119-123
Iodine status in pregnancy
Nina S. Dodd and Jagmeet Madan
Department of Foods Science and Nutrition,
SVT College of Home Science, SNDT Women's University, Bombay - 400
049, India.
The iodine status of 429 pregnant women in different
trimesters from the lower socio-economic strata of the urban slums
of Bombay was assessed using clinical and biochemical parameters.
The total goitre rate (TGR) of 45% and a visible goitre rate (VGR)
of 3.04% was observed. There was an evident increase in the TGR
during the months of pregnancy. The urinary iodine excretion pattern
revealed mild iodine deficiency. 55% of the women had urinary iodine
excretion less than 5 mcg/dl with 13.2% having less than 2 mcg/dl.
Elevated T3 and T4 levels were observed in
64 and 40% respectively of the women surveyed, while only 1.8% of
them had TSH levels higher than the normal range. No significant
difference in the levels of thyroid hormone (T3 or T4)
was noted between the euthyroid and goitrous subjects. The mean
TSH levels in euthyroid women were however significantly higher
than those with signs of goitre.
Introduction
The effects of iodine deficiency during pregnancy
on the growth and development of the foetus are of immense concern,
the most important being the effect on the brain1. It is
now well recognized that thyroid hormones are essential for the development
of the central nervous system. The lack of thyroid hormones during
the critical period of maturation of the CNS can result in morphological,
physiological and biochemical abnormalities. These effects also include
perinatal mortality and increased congenital anomalies2.
Iodine deficiency probably accounts for 90 000 still births and neonatal
deaths in India3. The need for monitoring maternal iodine
status and neonatal iodine status to prevent irreversible brain damage
has been emphasized. High incidence of neonatal chemical hypothyroidism
(NCH) has been reported from the endemic goitre regions of Asia, Africa,
South America and Europe4. In India the observed incidence
of NCH in endemic areas like Delhi, Kerala and Bombay was reported
to be six per 1000 births, one per 1000 births and one per 2481 births
respectively5,6. There is a lacunae of Indian studies with
regards to the iodine status and iodine deficiency disorders (IDD)
in pregnant women. Thus the present study was conducted with the following
objectives:
- To find out the prevalence of IDD in pregnant women
from the urban slums of Bombay.
- To assess the maternal iodine status during pregnancy.
Materials
and methods
The study comprised of a random sample of 429 pregnant
women in different trimesters, belonging to the lower socio-economic
strata of urban slums of Bombay. The subjects of the study comprised
of every third pregnant woman attending the antenatal clinics in the
Department of Obstetrics and Gynecology of a municipal hospital in
the suburbs of Bombay. The iodine status was assessed by clinical
and biochemical parameters. UNICEFWHO-ICCIDD classification for grading
goitre was followed7. Random casual urine samples were
collected in wide-mouthed polythene bottles, to which toluene was
added as a preservative. Urinary stable iodine estimation was carried
out by the modified Alkali Ash method described by Barker and associates8.
A 5 ml blood sample was drawn from each woman. The isolated serum
was used for estimation of thyroid hormones T3 and T4
by RIA and the level of TSH by IRMA using diagnostic kits obtained
from the Board of Isotope and Radiation Technology Bombay.
Results
The prevalence of goitre in pregnant women is given
in Table 1. The total goitre rate (TGR=la+2+3) was found to be 45%
and the visible goitre rate (VGR=2+3) of the women fell in grade 1a
and 1b where the gland needs to be palpated and enlargement is not
apparent. There was an evident increase in TGR and VGR during the
months of pregnancy. Goitre rate based on grade 1b was found to be
10%.
Table 1. Goitre prevalence in pregnant women.
| |
Grade of goitre |
TGR |
VGR |
| Month of pregnancy |
0 |
1a |
1b |
2 |
3 |
(%) |
(%) |
| <4 (n=30) |
19 (63.3) |
08 (26.6) |
03 (10) |
- |
- |
11 (2.5) |
- |
| 5 (n=43) |
21 (48.8) |
09 (20.9) |
06 (13.9) |
02 (4.6) |
- |
17 (3.9) |
02 (0.5) |
| 6 (n=64) |
37 (57.8) |
12 (18.7) |
13 (20.3) |
02 (3.1) |
- |
27 (6.3) |
02 (0.5) |
| 7 (n=230) |
124 (53.9) |
54 (23.4) |
44 (19.1) |
08 (3.4) |
- |
106 (24.8) |
08 (1.9) |
| 8 (n=59) |
32 (54.2) |
15 (25.4) |
10 (16.9) |
01 (1.6) |
- |
26 (6.08) |
01 (0.2) |
| 9 (n=7) |
02 (28.5) |
04 (57.1) |
01 (14.2) |
- |
- |
05 (1.17) |
- |
| Total (n=427) |
235 (55.0) |
102 (23.8) |
77 (18.03) |
13 (3.04) |
- |
192 (44.96) |
13 (3.04) |
Note: ( ) = Percentages
A total of 341 random casual urine samples were analysed
for urinary iodine excretion. The distribution pattern (Fig. 1) shows
94% of the women having urinary iodine excretion less than 10 mcg/dl,
54% less than5 mcg/dl and 13% less than 2 mcg/dl. Figure 2 shows the
urinary iodine excretion for the different grades of goitre. It was
observed that 49% of the women who did not show any thyroid enlargement
had urinary iodine excretion less than 5 mcg/dl. The majority of women
in grade la (68%) and grade 1b (67%) also showed deficient urinary
excretion, while 14% of women in grade 2 goitre had urinary iodine
excretion of moderate to severe iodine deficiency, ie >3.5 mcg/dl.
Figure 1. Distribution pattern of urinary iodine
excretion. *55% of the pregnant women had urinary
iodine excretion <5 ,m g/dl.
Figure 2. Urinary iodine excretion and grades
of goitre in pregnant women.
Table 2 shows the thyroid hormone levels in the different
months of pregnancy. Elevated T3 and T4 levels
were observed in 64% and 40% respectively of the women surveyed. (Normal
range: T3=0.7-2 mcg/ml T4=5.5-13.5 mcg/dl.)
In contrast only 1.8% of the subjects had TSH levels higher than the
normal range (0.2-5.1 m g/ml). No significant difference in the
levels of thyroid hormone (T3 or T4) were noted
between euthyroid and goitrous subjects. The mean TSH levels in euthyroid
women were however significantly higher than those with signs of goitre
(Table 3).
Table 2. Thyroid hormone levels in different
months of pregnancy.
| Month of pregnancy |
T3 (ng/ml) |
T4 (m g/ dl) |
TSH (m V/ml) |
| <4(n=31) |
2.32± 0.76 |
12.62± 3.62 |
0.97± 0.906 |
| 5 (n=38) |
2.51± 0.68 |
12.23± 2.19 |
1.41± 1.204 |
| 6 (n=67) |
2.36± 0.72 |
12.83± 2.50 |
1.32± 1.276 |
| 7(n=227) |
2.28± 0.71 |
12.98± 2.62 |
1.38± 0.91 |
| 8 (n=58) |
2.18± 0.68 |
12.82± 2.42 |
1.16± 0.70 |
| 9 (n=8) |
1.89± 0.61 |
12.03± 2.11 |
0.98± 0.26 |
| Normal range |
0.7-2.0 |
5.5-13.5 |
0.2-5.1 |
Discussion
The total goitre rate of 45% observed in the study
is high and is of concern. No published data about IDD prevalence
in Indian pregnant women were available for comparison. However, the
overall goitre rate as studied by an Indian Council of Medical Research
task force in Indian women9 was reported to be an average
of 26.8% in a cross-country survey covering 25 states of India. Thus
the goitre prevalence observed in the study is not unexpected, since
during pregnancy the thyroid is subjected to increased demands, which
is associated with a tendency to cause endogenous iodine deficiency.
Gestational changes in the thyroid have been recognized for centuries
and the ancient Egyptians relied on thyroid enlargement as a sign
of pregnancy.
Table 3. Thyroid hormone levels in euthyroid
and goitrous pregnant women.
| Grade |
T3 (ng/ml) |
T4 (m g/dl) |
TSH (m V/ml) |
| 0(n=233) |
2.30± 0.67 |
12.69± 2.75 |
1.49± 1.16 |
| 1a(n=105) |
2.20± 0.75 |
12.58± 2.93 |
1.12± 0.71 |
| 1b(n=79) |
2.44± 0.09 |
13.19± 2.59 |
1.06± 0.64 |
| 1l(n=12) |
2.19± 0.66 |
13.16± 2.69 |
1.17± 1.26 |
| Normal range |
0.7-2.0 |
5.5-13.5 |
0.2-5.1 |
An evident increase in the total goitre rate during
the months of pregnancy can be attributed to the increased demands
of foetal growth. Goitre rate based on grade 1b of 18% observed in
the present study is much above the criteria of 5% set by WHO11
in pre- and peri-adolescent age groups, for the problem to be considered
of public health significance.
In normal pregnancy the thyroid gland undergoes changes
in both structure and function. By the end of the first trimester
renal reabsorption of iodine falls and this results in an increased
urinary iodine excretion and a relative deficiency in plasma iodine12.
There was an evident increase in the mean urinary iodine excretion
during the months of pregnancy in the present study though it was
lower than 5 mcg/dl, a level associated with normal iodine status
except for the eighth month of pregnancy where the mean iodine excretion
was found to be 5.6 mcg/dl.
The urinary iodine excretion pattern observed in the
population surveyed is closer to the distribution pattern expected
in a population with mild iodine deficiency13. This level
of iodine deficiency is usually not accompanied by hypothyroidism
and cretinism14. The majority of women (68% and 67%, respectively)
with grade 1a and 1b goitre had low urinary iodine excretion. Lower
urinary iodine excretion in goitrous as compared to nongoitrous pregnant
women has been reported15. A high percentage of women (49%)
with no apparent signs of goitre also showed low urinary iodine excretion
with 14% having less than 2 mcg/dl, a level associated with severe
iodine deficiency, thereby suggesting these women to be at risk to
hypothyroidism.
The subjects studied had T3 and T4
levels higher than the normal values. 64% of the women had high T3
and 40% had high T4 levels. Only 1.8% of the subjects had
TSH levels higher than the normal range. Elevated T3 and
T4 levels and normal TSH levels during pregnancy have been
reported by other workers16, which was also observed in
the study. The hormonal profile of the pregnant women studied was
consistent with the normal physiological changes in the thyroid during
pregnancy. The thyroidal activity is enhanced during gestation as
a result of the increased glandular adjustments to the lowering of
the free hormones, the direct stimulation by HCG (early gestation)
and TSH (late gestation) and the reduced availability of iodine17.
When thyroid hormone levels of women in different months were compared,
it was observed that TSH levels were significantly lower in the early
months as compared to the later part of gestation. This could be attributed
to partial pituitary blunting due to increased levels of HCG in early
gestation. No significant difference in the levels of thyroid hormones
(T3 or T4) was noted between euthyroid and goitrous
subjects. Similar observations have been made by other workers15.
It is known that compensatory enlargement of thyroid gland ensues
following the physiological demand for thyroid hormones during pregnancy
and other stages like puberty and even menstruation17 .
Thus to conclude, the results of the present study
suggest that mild to moderate iodine deficiency is a public health
problem in pregnant women from the urban slums of Bombay. This is
reflected by: (i) high total goitre rate of 45% and grade 1b goitre
rate of 18% (ii) 54% of the women with urinary iodine excretion less
than 5 mcg/dl which is related to iodine deficiency (iii) 67% to 68%
of the women with grade la and 1b goitre having urinary iodine excretion
less than 5 mcg/dl. Thus pregnant women from the urban slums of Bombay
are at risk of hypothyroidism which is of concern as it is associated
with the potential risk of irreversible damage to the foetus.
Acknowledgments--Thanks are due to Dr M.G. Karmarkar, Dr C.S. Pandav (All India Institute
of Medical Science, New Delhi) and Dr (Mrs) K.D. Nihalani (Nair Hospital,
Bombay) for their technical guidance in this study. We are also indebted
to Dr M.S. Paralkar (Medical Superintendent, Bhabha Municipal Hospital,
Bandra (W), Bombay) for granting permission to conduct the study.
This work is a part of the research 16 project on 'Iodine Deficiency
Control, India' (3-P-890227), supported by International Development
Research Corporation, Ottawa, Canada.
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Copyright © 1993 [Asia Pacific Journal of Clinical
Nutrition]. All rights reserved.
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