thyroid disease is the second most common endocrine condition encountered in women of childbearing age after diabetes . most of these conditions are treatable , and may affect mother and fetus adversely if they are not evaluated and managed appropriately . , there is an increase in thyroxine ( t4 ) and triiodothyronine ( t3 ) production , which results in inhibition of thyroid - stimulating hormone ( tsh ) in the first trimester of pregnancy , due to a high human chorionic gonadotropin ( hcg ) level that stimulates the tsh receptor because of partial structural similarity [ figure 1 ] . a large plasma volume and thus an altered distribution of thyroid hormone , increased thyroid hormone metabolism , increased renal clearance of iodide , and higher levels of hepatic production of thyroxine - binding globulin ( tbg ) in the hyperestrogenic state of pregnancy are responsible for higher thyroxine requirements in pregnancy . it is very important to remember that biochemical thyroid function should be free thyroid hormone , as total hormone will mislead showing more than normal value when the patient is euthyroid . thyroid hormone profile in the mother and fetus during pregnancy clinical or subclinical thyroid disorders are usually detected during pre - conceptional counseling or in women who have just conceived and have done tests for thyroid function . according to recent american thyroid association ( ata ) guidelines , if laboratory - dependent , trimester - specific ranges for tsh are not available , the recommended reference ranges for tsh are 0.1 to 2.5 miu / l in the first trimester , 0.2 to 3.0 miu / l in the second trimester , and 0.3 to 3.0 the typical case is a women in the first trimester of pregnancy who is referred with a high tsh value with the free thyroid hormones in the low normal range or with frank hypothyroidism and in certain instances with biochemical euthyroxinemia with tpo antibody positivity . the presence of thyroid antibody , even in euthyroid patients , has been shown to be associated with increased number of miscarriage , perinatal death , and postpartum dysfunction , low motor and intellectual development in the offspring . but , till now , biochemical normal thyroid test with positive antibody do not make a case for thyroxine supplement . maternal hypothyroidism has been associated with increased risk of low birth weight , fetal distress , and impaired neuropsychological development . haddow and colleagues described a 7-point iq deficit in 7- to 9-year - old children born to untreated hypothyroid women when compared with age - matched children born to euthyroid women of less than 85 , compared with 5% of controls . all women with overt and subclinical hypothyroidism should be treated irrespective of thyroid peroxidase ( tpo ) antibody positivity with lt4 during pregnancy to maintain serum tsh in the trimester - specific goal range . it has been recommended to check serum tsh every four weeks during pregnancy so that appropriate dose adjustments can be made , but our routine practice is to check every six weeks . the recommended therapy is with oral lt4 , which should be taken on an empty stomach ( 45 minutes before consumption of food , beverages , or other medications ) . in addition , calcium , iron , and prenatal vitamin supplements should be avoided within four hours of ingestion of lt4 , as these can decrease the absorption of thyroxine . in a typical case , the dose requirement goes up as pregnancy advances , as pregnancy is a hypermetabolic condition [ table 1 ] . we keep on counseling patients on this so that their compliance remains perfect . showing the biochemistry and requirement of thyroxine in pregnancy in a patient with primary hypothyroidism , bhattacharyya a et al . immediately after delivery , the requirement of the thyroxine drops and women who were taking thyroixine prior to pregnancy will shift to their pre - pregnancy dose and those who started their thyroxine in pregnancy will require half the dose they were taking just before delivery . in women who had started their thyroxine in pregnancy for subclinical hypothyroidism , the medication can be stopped after delivery and thyroid balance re - assessed again after six weeks and decision taken regarding continuation of treatment . obviously , some of these women goes through post - partum thyroiditis and requires thyroxine replacement for a longer time . , there may be deterioration in control due to reduced absorption of medication secondary to vomiting or to hcg - driven stimulation of tsh receptors . in the third trimesters , typically , treatment doses can be reduced due to the immune - suppressant effects of pregnancy as is seen in other autoimmune conditions like rheumatoid arthritis , systemic lupus etc . the typical ill - effects in pregnancy are accelerated hyperemesis of pregnancy requiring repeated hospital admission for intravenous fluid therapy , repeated miscarriage , poor growth of fetus , premature delivery , pregnancy - induced hypertension , etc . untreated mother can also develop thyrotoxic crisis , fortunately rare now with an early diagnosis and effective treatment . fetal graves disease is very rare and happens due to transplacental transfer of tsh - receptor stimulating antibody . hyperthyroidism if diagnosed before conception is best treated before conception in case radioactive iodine is given ; current recommendation is not to conceive for at least four months . neonatal outcome is better with fewer anomalies and there is lower chance of delivering prematurely if euthyroidism is achieved prior to conception , when compared with those women in whom either control is achieved in early pregnancy or later pregnancy , in a stepwise manner . there is chance that they will develop hypothyroidism ; we can tackle that with thyroxine replacement as has been detailed earlier . for people diagnosed in the current pregnancy , we straightway start with anti - thyroid medication . our aim is to keep free t4 in the upper normal range , sometime tsh can be little lower than normal range , but we concentrate more of free t4 as we know tsh takes time to get settled . block and replace regimen is not followed in pregnancy as thyroxine does not cross placenta freely but anti - thyroid medications do . the dose of ptu depends on the control , sometime goes even up to 400 - 800 mg / day . liver function tests should be monitored with ptu , as there is a risk of hepatotoxicity . methimazole is not preferred in the first trimester due to the risk of aplasia cutis and the spectrum of birth defects in pregnancy . as the pregnancy advances , dose requirement comes down in most of the cases ; one - third of pregnant women can actually stop anti - thyroid medication in the third trimester [ table 2 ] . our routine practice is to check the thyroid function two weeks after delivery as opposed to six to eight weeks in cases of hypothyroidism . beta - blockers , if necessary , can be given for a short duration for controlling symptoms . when thyroidectomy is needed for the control of hyperthyroidism , it should be planned in the second trimester of pregnancy ; fortunately , this is very rare , and none of the authors can remember a single case they referred to surgeons for uncontrolled hyperthyroidism in pregnancy . showing the thyroid function and treatment of a patient with graves disease in pregnancy treated by the authors ( unpublished ) breast feeding while on anti - thyroid medication remains a sensitive issue ; ptu is the preferred medicine as it is more protein - bound and is secreted least in breast milk . up to 600 mg a day ptu is considered safe ; it is recommended to keep an eye on growth of the baby clinically with biochemical test for thyroid function if suspected for growth problem . gestational hyperthyroidism or gestational thyrotoxicosis is used when there are symptoms of hyperthyroidism due to the high levels of hcg , which causes thyroid hyperfunction . this condition needs to be differentiated from graves disease , as most of the symptoms are similar to those in pregnancy . up to 15% of normal pregnancy tsh can be suppressed due to hcg effect ; they do not require extra treatment ; careful observation is good enough . there is another entity in pregnancy called transient gestational thyroticosis , where free thyroid hormone can be increased , and they require a short course of anti - thyroid medication . thyroid cancer is the most common endocrine malignancy affecting about 14 of 100000 pregnant women . the types of cancers seen in pregnant women are the same as in non - pregnant women . if the cancer is well - differentiated , surgery can be done in the immediate postpartum period ; however , in not well - differentiated cancers , surgery can be done in the second trimester . post - surgery , radioiodine scan and ablation is absolutely contraindicated during pregnancy and lactation . in women who have been operated and are on suppressive treatment with levothyroxine clinical or subclinical thyroid disorders are usually detected during pre - conceptional counseling or in women who have just conceived and have done tests for thyroid function . according to recent american thyroid association ( ata ) guidelines , if laboratory - dependent , trimester - specific ranges for tsh are not available , the recommended reference ranges for tsh are 0.1 to 2.5 miu / l in the first trimester , 0.2 to 3.0 miu / l in the second trimester , and 0.3 to 3.0 the typical case is a women in the first trimester of pregnancy who is referred with a high tsh value with the free thyroid hormones in the low normal range or with frank hypothyroidism and in certain instances with biochemical euthyroxinemia with tpo antibody positivity . the presence of thyroid antibody , even in euthyroid patients , has been shown to be associated with increased number of miscarriage , perinatal death , and postpartum dysfunction , low motor and intellectual development in the offspring . but , till now , biochemical normal thyroid test with positive antibody do not make a case for thyroxine supplement . maternal hypothyroidism has been associated with increased risk of low birth weight , fetal distress , and impaired neuropsychological development . haddow and colleagues described a 7-point iq deficit in 7- to 9-year - old children born to untreated hypothyroid women when compared with age - matched children born to euthyroid women of less than 85 , compared with 5% of controls . all women with overt and subclinical hypothyroidism should be treated irrespective of thyroid peroxidase ( tpo ) antibody positivity with lt4 during pregnancy to maintain serum tsh in the trimester - specific goal range . it has been recommended to check serum tsh every four weeks during pregnancy so that appropriate dose adjustments can be made , but our routine practice is to check every six weeks . the recommended therapy is with oral lt4 , which should be taken on an empty stomach ( 45 minutes before consumption of food , beverages , or other medications ) . in addition , calcium , iron , and prenatal vitamin supplements should be avoided within four hours of ingestion of lt4 , as these can decrease the absorption of thyroxine . in a typical case , the dose requirement goes up as pregnancy advances , as pregnancy is a hypermetabolic condition [ table 1 ] . we keep on counseling patients on this so that their compliance remains perfect . showing the biochemistry and requirement of thyroxine in pregnancy in a patient with primary hypothyroidism , bhattacharyya a et al . immediately after delivery , the requirement of the thyroxine drops and women who were taking thyroixine prior to pregnancy will shift to their pre - pregnancy dose and those who started their thyroxine in pregnancy will require half the dose they were taking just before delivery . in women who had started their thyroxine in pregnancy for subclinical hypothyroidism , the medication can be stopped after delivery and thyroid balance re - assessed again after six weeks and decision taken regarding continuation of treatment . obviously , some of these women goes through post - partum thyroiditis and requires thyroxine replacement for a longer time . conception is usually more of a problem in untreated hyperthoidism . majority of the disorders are due to graves disease . in the first trimester , there may be deterioration in control due to reduced absorption of medication secondary to vomiting or to hcg - driven stimulation of tsh receptors . in the third trimesters , typically , treatment doses can be reduced due to the immune - suppressant effects of pregnancy as is seen in other autoimmune conditions like rheumatoid arthritis , systemic lupus etc . the typical ill - effects in pregnancy are accelerated hyperemesis of pregnancy requiring repeated hospital admission for intravenous fluid therapy , repeated miscarriage , poor growth of fetus , premature delivery , pregnancy - induced hypertension , etc . untreated mother can also develop thyrotoxic crisis , fortunately rare now with an early diagnosis and effective treatment . fetal graves disease is very rare and happens due to transplacental transfer of tsh - receptor stimulating antibody . hyperthyroidism if diagnosed before conception is best treated before conception in case radioactive iodine is given ; current recommendation is not to conceive for at least four months . neonatal outcome is better with fewer anomalies and there is lower chance of delivering prematurely if euthyroidism is achieved prior to conception , when compared with those women in whom either control is achieved in early pregnancy or later pregnancy , in a stepwise manner . there is chance that they will develop hypothyroidism ; we can tackle that with thyroxine replacement as has been detailed earlier . for people diagnosed in the current pregnancy , we straightway start with anti - thyroid medication . our aim is to keep free t4 in the upper normal range , sometime tsh can be little lower than normal range , but we concentrate more of free t4 as we know tsh takes time to get settled . block and replace regimen is not followed in pregnancy as thyroxine does not cross placenta freely but anti - thyroid medications do . the dose of ptu depends on the control , sometime goes even up to 400 - 800 mg / day . liver function tests should be monitored with ptu , as there is a risk of hepatotoxicity . methimazole is not preferred in the first trimester due to the risk of aplasia cutis and the spectrum of birth defects in pregnancy . as the pregnancy advances , dose requirement comes down in most of the cases ; one - third of pregnant women can actually stop anti - thyroid medication in the third trimester [ table 2 ] . our routine practice is to check the thyroid function two weeks after delivery as opposed to six to eight weeks in cases of hypothyroidism . beta - blockers , if necessary , can be given for a short duration for controlling symptoms . when thyroidectomy is needed for the control of hyperthyroidism , it should be planned in the second trimester of pregnancy ; fortunately , this is very rare , and none of the authors can remember a single case they referred to surgeons for uncontrolled hyperthyroidism in pregnancy . showing the thyroid function and treatment of a patient with graves disease in pregnancy treated by the authors ( unpublished ) breast feeding while on anti - thyroid medication remains a sensitive issue ; ptu is the preferred medicine as it is more protein - bound and is secreted least in breast milk . up to 600 mg a day ptu is considered safe ; it is recommended to keep an eye on growth of the baby clinically with biochemical test for thyroid function if suspected for growth problem . gestational hyperthyroidism or gestational thyrotoxicosis is used when there are symptoms of hyperthyroidism due to the high levels of hcg , which causes thyroid hyperfunction . this condition needs to be differentiated from graves disease , as most of the symptoms are similar to those in pregnancy . up to 15% of normal pregnancy tsh can be suppressed due to hcg effect ; they do not require extra treatment ; careful observation is good enough . there is another entity in pregnancy called transient gestational thyroticosis , where free thyroid hormone can be increased , and they require a short course of anti - thyroid medication . thyroid cancer is the most common endocrine malignancy affecting about 14 of 100000 pregnant women . the types of cancers seen in pregnant women are the same as in non - pregnant women . if the cancer is well - differentiated , surgery can be done in the immediate postpartum period ; however , in not well - differentiated cancers , surgery can be done in the second trimester . post - surgery , radioiodine scan and ablation is absolutely contraindicated during pregnancy and lactation . in women who have been operated and are on suppressive treatment with levothyroxine thyroid disorders are common in pregnancy , and the most common disorder is subclinical hypothyroidism . early and effective treatment of thyroid disorder ensures a safe pregnancy with minimal maternal and neonatal complications .
thyroid disorders are common in pregnancy and the most common disorder is subclinical hypothyroidism . due to the complex hormonal changes during pregnancy 
 , it is important to remember that thyroxine requirements are higher in pregnancy . 
 according to recent american thyroid association ( ata ) guidelines , the recommended reference ranges for tsh are 0.1 to 2.5 
 miu / l in the first trimester , 0.2 to 3.0 miu / l in the second trimester , and 0.3 to 3.0 
 miu / l in the third trimester . 
 maternal hypothyroidism is an easily treatable condition that has been associated with increased risk of low birth weight , fetal distress , and impaired neuropsychological development . 
 hyperthyroidism in pregnancy is less common as conception is a problem . 
 majority of them are due to graves disease , though gestational hyperthyroidism is to be excluded . preferred drug is propylthiouracil ( ptu ) with the target to maintain free t4 in upper normal range . 
 doses can be reduced in third trimester due to the immune - suppressant effects of pregnancy . 
 early and effective treatment of thyroid disorder ensures a safe pregnancy with minimal maternal and neonatal complications .