The association between TD and adverse pregnancy outcomes has been studied earlier in western countries [6
]. This has scarcely been studied in Indian population except two studies which looked at the prevalence of hypothyroidism in pregnant females [10
The mean age at presentation is lower (25.19 ± 4.17 years) compared to Western studies, namely, 27 ± 6 years [12
], 29 ± 5 years [9
] reflecting early marriage and early conception prevalent in India. The mean gestational age at presentation was 10.03 (±1.87) weeks indicating that most of the pregnant women in India do not visit the antenatal clinic during the first 8 weeks of gestation.
Our study demonstrates a higher incidence of hypothyroidism and TAI. The prevalence of hypothyroidism in this cohort is 4.8% which is higher than that in the western literature (2.5% [13
], 2.6% [12
]) and a previous Indian study (3.69% [11
]). The higher prevalence in our study could be due to the higher prevalence of TAI in our cohort (12.4% versus 6.5% [13
] and 8% [12
]). Studies systematically assessing the prevalence of TAI during pregnancy, however, have not been reported from India. Iodine deficiency could be a contributory cause, but this information cannot be generated from our study as urinary iodine estimation was not done. The percentage of households consuming iodised salt in India as per the Iodine Network Global score card 2010 is 51% [14
In the present study, the probable reason for higher miscarriage in patients with hypothyroidism was that they might have had undetected hypothyroidism at conception, and the treatment might have been insufficient to restore euthyroidism. The higher age (mean = 29 years) could also have contributed to miscarriage. Abalovich et al. [9
] showed that untreated hypothyroidism, subclinical, or overt, at the time of conception is associated with miscarriage rate of 31.4% compared with 4% in euthyroid subjects at conception. The prevalence of stillbirth and premature delivery was not significantly higher than that in our hypothyroid patient population probably due to the adequate treatment given to the patients to maintain euthyroid state.
The miscarriage rate was 3 times more common in subjects with TAI (7.35 versus 26.5%) in our cohort (). The association has previously been established by various studies [6
]. TAI may be viewed as a marker of generalized immune imbalance that will explain the rejection of fetal graft [15
]. Presence of TAI could be associated with a subtle thyroid hormone deficiency, due to the reduced functional reserve characteristic of chronic thyroiditis [15
]. Women with thyroid antibodies tend to become pregnant at an average 3-4 years later and are, therefore, more prone to pregnancy loss. In our cohort, the relatively higher age in the patients with miscarriage might also have contributed to pregnancy loss.
In subjects with TSH <2μ
IU/mL with TAI, history of stillbirth was significantly higher suggesting the association between thyroid autoimmunity and pregnancy loss. Some of the previous studies showed higher number of premature deliveries in women with TAI compared to normal women [9
]. Our study did not reveal such association.
Thyroid function in subjects with TSH 2–4μ
IU/mL without TAI showed significant increase in TSH and decrease in FT3 and FT4 at 6 months compared to baseline. The significant decline in thyroid functions for this subgroup at the latter half of pregnancy may justify thyroxine supplementation and regular monitoring (though presently not recommended) in this subgroup in the second half of gestation.
Patients with TSH 2–4μ
IU/mL with TPOAb positivity were treated with thyroxine. The rationale for opting for treatment in these patients is the fact that despite the TSH downregulation in the first trimester by hCG, TSH level is in the upper half of normal, and there would be a tendency for progressive decline in thyroid function since they have TAI [16
]. Though it is recommended to perform FT4 estimation before initiating treatment (in low-normal or low FT4) in this subset of individuals, the lack of trimester-specific normal values for FT4 and the inherent problems with FT4 assay made us focus on serum TSH as the marker for initiating and monitoring treatment. There was no significant difference in the pregnancy outcome in this group of patients compared to normal. This may be due to the smaller number of patients in this subset and the treatment given to these patients.
The prevalence of GTT in the cohort was 6.4%. In India, the prevalence of GTT has not been assessed previously. The prevalence of GTT varies from 2-3% in the Western literature [17
]. The prevalence of GD in this cohort is 0.6%, higher than that published in the Western literature (0.2–0.4%) [18
]. Further conclusions could not be derived since the sample size was small.
Our data gives a prevalence of thyroid dysfunction in subjects attending a tertiary care centre in Western India which can be generalized to population in the same setting in other parts of India. One limitation of our study was that 21% of subjects were lost to follow up. The Endocrine Society guidelines suggest that universal thyroid screening during pregnancy cannot be recommended, and aggressive case finding is recommended in specific subsets of subjects [5
]. But recent studies have shown that targeted case finding will miss around 30–50% cases of hypothyroidism and/or TAI [12
]. This is similar to the present study in which 40% of the hypothyroid and 45% of TPOAb positive patients did not have high-risk characteristics. Approximately 60% of the hypothyroid or TPOAb positive pregnant women could have been missed by targeted case finding.