pregnancy has a profound physiological impact on the thyroid gland and thyroid function . during pregnancy ,
the thyroid gland increases in size by 10% in iodine sufficient countries and to a greater extent in iodine deficiency countries .
production of thyroid hormones and iodine requirement both increases by approximately 50% during pregnancy as part of physiology .
in addition , pregnancy is a stressful condition for the thyroid gland resulting in hypothyroidism in women with limited thyroid reserve or iodine deficiency .
data from recently published studies have underscored the association between miscarriage and preterm delivery in women with normal thyroid function who test positive for thyroid peroxidase ( tpo ) antibodies .
prenatal and postnatal adverse effects including attention deficit and hyperactivity syndrome have been reported in children born to hypothyroid mothers . during the first trimester ,
approximately 1 in 10 pregnant women develop antibodies to tpo or thyroglobulin and hypothyroidism develops in roughly 16% of these women .
there are a few reports of prevalence of hypothyroidism during pregnancy from india with prevalence rates ranging from 4.8% to 11% .
therefore , this study was carried out in a larger cohort of pregnant women during the first trimester from a government hospital setting catering to majority of women from lower socioeconomic status .
this was a cross - sectional multicenter study conducted at allahabad , bengaluru , rohtak , chennai , kolkata , hyderabad , nasik , pune , new delhi , srinagar , and vizag to assess the incidence of hypothyroidism in pregnant women .
complete blood count ( hemogram ) , total cholesterol , triglycerides , serum creatinine , and blood urea nitrogen were evaluated for all subjects .
estimation of thyroid stimulating hormone ( tsh ) , free t4 , and anti - tpo antibodies was carried out using roch modular kit using eclia technology .
the intra - assay precision of tsh and free t4 was 3 and 2 , whereas interassay precision was 7.2 and 4.8 , respectively .
the mean age of the study population was 25.5  5.6 years with a mean gestational age of 19.3  15.9 weeks .
demographic characteristics of the study population ( n=2955 ) keeping upper normal limit of tsh < 4.5 , we found in our study population 13.13% of pregnant women to be hypothyroid ( n = 388 ) . anti - tpo antibodies were positive in 20.74% of all pregnant women (
n = 613 ) , whereas 40% ( n = 155 ) of hypothyroid pregnant women were positive for anti - tpo antibodies .
a total of 36.07% ( n = 816 ) of pregnant women were found to be hypothyroid when we used trimester - specific tsh reference ranges as suggested by the american thyroid association ( ata ) [ table 2 ] .
thyroid profile of pregnant women the prevalence of hypothyroidism was 15.1% , 12.06% , and 14.36% in the first , second , and third trimester , respectively , whereas anti - tpo antibody positivity was seen in 18.07% , 19.45% , and 22.91% in each trimester [ table 2 ] .
miu / l for the second and third trimester as suggested by ata , we found 44.3% , 32.0% , and 34% women were found to have hypothyroidism in the first , second , and third trimester , respectively [ table 2 ] .
when we analyzed prevalence of hypothyroidism in individual states / cities , srinagar ( kashmir ) , reported unusually high prevalence of hypothyroidism of ( 39% ) and the lowest prevalence was reported from bengaluru ( karnataka ) ( 7.8% ) [ table 3 ] .
this study was aimed to evaluate thyroid function during different trimesters of pregnancy in a large cohort across india .
the major findings are that 13.3% women attending secondary and tertiary public hospitals have hypothyroidism majority being subclinical .
the prevalence of hypothyroidism has been reported from different countries very recently . on analysis , results of this study are consistent with recently published data from india and other countries .
previous studies conducted in delhi reported a 14.3% prevalence of hypothyroidism during the first trimester .
there are at least two small - scale published studies from the south , one from chennai , and another from hyderabad .
rao et al . included 163 nonpregnant women with recurrent pregnancy loss in a gestational age up to 12 weeks ( 2006 ) in hyderabad .
similarly , in a community - based large - scale study involving over 500,000 pregnant women from the usa showed a 15.5% prevalence of hypothyroidism .
hypothyroidism was found in 7 ( 4.12% ) women with recurrent pregnancy loss and one in the control group .
the study demonstrates that hypothyroidism has a statistically significant relationship with recurrent pregnancy loss in the first trimester .
another study examined 500 pregnant women attending two government obstetrics and gynecology hospitals in chennai for a period of 5 months in 2007 for thyroid function .
subclinical hypothyroidism was detected in 2.8% , among them , tpo antibodies positivity was seen in 57.1% , whereas euthyroid women had significantly lower positivity ( 7% ) . in another study ,
sahu et al . have done thyroid function during the second trimester in high - risk pregnant women and reported that prevalence of thyroid disorders , especially overt and subclinical hypothyroidism was 6.47% .
further , in this study , significant adverse effects on maternal and fetal outcomes were observed emphasizing the importance of routine antenatal thyroid screening .
therefore , findings of our study are consistent with other previously reported data from india and this study also shows a rising trend of hypothyroidism among the indian pregnant women .
the impact of thyroid dysfunction on pregnancy outcomes appears to manifest with a tsh threshold of > 2.5
miu / l in the first trimester rather than with a tsh range based on percentiles cutoff derived from apparently  normal  pregnant women .
ata recommends > 2.5 and > 3.0 iu / ml as cutoff range for diagnosis of hypothyroidism during the first and later part of pregnancy , respectively .
however , we have taken 4.5 iu / ml as cutoff for diagnosis of hypothyroidism in different trimesters .
in addition , marwaha et al . have reported that normal range of thyroid hormones in the indian pregnant women are higher as compared to international cutoffs .
the large burden of subclinical hypothyroidism in pregnancy may prove to be a major public health burden in india , once it becomes clear that adverse outcomes can be corrected with screening and early replacement of levothyroxine .
children born to hypothyroid mothers have a poor intellectual function during the later part of their life .
therefore , majority of the developed countries have the national neonatal screening program in place and routinely screen all newborn for hypothyroidism . the question whether to screen all pregnant women for hypothyroidism
ata in its recently published guidelines has stated against the universal screening of pregnant women for hypothyroidism . some of these studies have shown an adverse effect on fetal and maternal health outcomes . however , these studies are too small , and it is advisable that a large - scale study is done in this regard from india .
the strong point of this study is that we have included the largest number of subjects in this study from different parts of india .
further , the study population belongs to different socioeconomic strata and therefore , represents probably the pregnant population of india .
this study also demonstrates a secular trend in prevalence of hypothyroidism in india , when data from other previous studies was analyzed . however , there are few limitations of this study .
we have not carried out clinical and radiological thyroid examination including ultrasound , and apart from autoimmunity , we have not evaluated other causes of hypothyroidism in these women .
this study concludes that there is a high prevalence of hypothyroidism in pregnancy ( 13.13% ) .
further studies are required to evaluate impact of thyroid disorders during pregnancy in the indian population to decide whether universal screening is needed for indian pregnant women .
 background : a previous hospital based study from delhi revealed a high prevalence of hypothyroidism in pregnant women . 
 several other studies with small sample size also indicate a rising trend of prevalence of hypothyroidism during pregnancy in india.objective:to assess prevalence of hypothyroidism in pregnant women from various states / cities across india.materials and methods : this was a cross - sectional multicenter study conducted at allahabad ( uttar pradesh ) , bengaluru ( karnataka ) , chennai ( tamil nadu ) , kolkata ( west bengal ) , hyderabad ( telangana ) , nasik ( maharashtra ) , rohtak ( haryana ) , pune ( maharashtra ) , new delhi ( delhi ) , srinagar ( kashmir ) , and vizag ( andhra pradesh ) enrolling 2599 pregnant women . 
 estimation of thyroid stimulating hormone ( tsh ) , free t4 , and antithyroid peroxidase ( tpo ) antibodies was carried out using roche modular kit using eclia technology in a central laboratory.results:we found in our study population that 13.13% of pregnant women have hypothyroidism ( n = 388 ) , using a cutoff tsh level of 4.5 iu / ml . 
 this prevalence was much higher using the american thyroid association criteria . 
 anti - tpo antibodies were positive in 20.74% of all pregnant women ( n = 613 ) , whereas 40% ( n = 155 ) of hypothyroid pregnant women were positive for anti - tpo antibodies.conclusion:this study concludes that there is a high prevalence of hypothyroidism ( 13.13% ) , majority being subclinical in pregnant women during the first trimester from india and universal screening of hypothyroidism may be desirable in our country . 