however , nearly 10% of abnormal thyroid function was observed according to thyroid function survey using general health checkup system for the adult in japan .
this implicates that pregnant women in japan also have higher prevalence of thyroid dysfunction . up to now , there are no large population studies regarding the prevalence of thyroid dysfunction in pregnant women in japan .
a well - known complication is low intelligence quotient in the infants born from mothers with overt hypothyroidism .
thyroid dysfunctions are also associated with several obstetrical complications such as preeclampsia and placental abruption [ 710 ] .
consequently , there is a question whether the management of thyroid dysfunction could reduce these complications on both mother and child during pregnancy .
currently , no consensus has been reached on the universal screening for thyroid function for pregnant women .
acog recommended thyroid function screening during pregnancy should be limited to women with symptoms of thyroid disease and those with a history of thyroid disease or other medical conditions associated with it .
however , this conventional screening may be insufficient because most of pregnant women that have thyroid dysfunction are asymptomatic and without a history of thyroid disease .
therefore , consideration should be given to extend the screening objects including women with possible thyroid disease except for women with symptoms of thyroid disease and those with a history of thyroid disease .
here , we conducted a study to see the incidence of thyroid dysfunction in pregnant women having obstetrical or medical complications .
if we obtain a high incidence of thyroid dysfunction in some high - risk groups , a more reasonable approach for screening would be provided .
this study was undertaken retrospectively and there was no need to be approved by a suitably constituted ethics committee of our institution .
we retrospectively reviewed the medical charts of women with obstetrical or medical complications that were admitted to the perinatal center of miyazaki medical association hospital from january 2001 to april 2011 .
our hospital mainly deals with referral cases in the central part of miyazaki province , japan .
the total number of deliveries was 4381 in the study period . in miyazaki province , when antepartum high - risk factors are diagnosed , women are advised to visit high - level perinatal centers where they finally deliver their babies .
high - risk factors include prenatal medical complications such as diabetes , obstetric complications such as hypertensive disorders , and fetal complications such as growth restriction . additionally , some emergencies may occur and they are transferred to the 8 high - level centers . as a consequence , 80% of total deliveries ( pregnant women without risk ) were carried out in private clinics .
the rest deliveries with high - risk factors were carried out in 8 high - level centers .
pregnant women with the following complications were selected : women with symptoms of thyroid disease and those with a personal history of thyroid disease ( thyroid disease ) , intrauterine growth restriction ( iugr ) , diabetes mellitus ( diabetes ) , hypertension , intrauterine fetal death ( iufd ) , and placental abruption ( abruption ) . the signs and symptoms of hyperthyroidism included tremors , nervousness , insomnia , excessive sweating , heat intolerance , tachycardia , hypertension , and goiter .
the signs and symptoms of hypothyroidism included fatigue , muscle cramps , constipation , cold intolerance , and hair loss .
the history of thyroid disease was either known hyperthyroidism such as graves ' disease or hypothyroidism such as hashimoto thyroiditis , subacute thyroiditis , and iodine deficiency .
iugr was defined as sex - specific birth weight less than the 10th percentile for gestational age according to the japanese standard growth curve for singletons .
diabetes was defined as either preexisting diabetes mellitus or gestational diabetes mellitus based on 75  g glucose tolerance test .
gestational diabetes mellitus is diagnosed , if one or more of these readings are elevated in this study ; at fasting 100  mg / dl , at 1-hour 180  mg / dl and at 2-hour 150  mg / dl .
preeclampsia was diagnosed when hypertension ( systolic 140  mmhg or 90  mmhg diastolic ) and proteinuria ( dipstick 2 + ) developed after 20 weeks of gestation .
gestational hypertension was diagnosed when hypertension ( systolic 140  mmhg or 90  mmhg diastolic ) without proteinuria developed after 20 weeks of gestation .
chronic hypertension was defined as hypertension diagnosed prior to conception or within the first 20 weeks of pregnancy .
placental abruption was determined by the presence of retroplacental hematoma and clinical presentations ( any one or combination of genital bleeding , abdominal pain , pregnancy - induced hypertension , premature labor , premature rupture of membrane , iufd , or nonreassuring fetal status ) . in case of placental abruption with pregnancy - induced hypertension or iufd ,
a total of 838 pregnancies displaying obstetrical or medical complications were found in the study period . from the 838 pregnancies
, we selected the 392 cases that had examined thyroid function test from 1st to 3rd trimesters .
they were iugr ( n = 115 ) , diabetes ( n = 115 ) , hypertension ( n = 63 ) , iufd ( n = 52 ) , abruption ( n = 15 ) , and thyroid disease ( n = 32 ) . the test of thyroid function was done in our hospital .
serum concentrations of tsh and free t4 ( ft4 ) were measured by electro chemiluminescence immunoassay or chemiluminescent enzyme immunoassay ( abbott japan , architect tsh , ft4 ) .
mu / l in 3rd trimester ) and normal - to - high ft4 ( > 0.7  ng / dl ) .
mu / l in 1st trimester , > 3.0 in 2nd and 3rd trimesters ) and normal - to - low ft4 ( < 1.8  ng / dl ) .
low ft4 ( < 0.7  ng / dl ) with normal - to - low tsh was categorized as hypothyroidism .
high ft4 ( > 1.8  ng / dl ) with normal - to - high tsh was categorized as hyperthyroidism .
mu / l ) in conjunction with low ft4 ( < 0.7  ng / dl ) or high tsh ( 10.0 
mu / l ) in conjunction with high ft4 ( 1.8  ng / dl ) .
the alterations in thyroid function during pregnancy can pose challenges to the interpretation of laboratory thyroid tests .
therefore , we used trimester - specific reference intervals for thyroid function , following the guidelines of the american thyroid association .
the following clinical characteristics were also collected : maternal age , parity , gestational age at examination of thyroid function ( weeks ) , gestational age at delivery ( weeks ) , birth weight ( g ) , and cesarean delivery .
perinatal outcomes were investigated and included evaluations of umbilical artery ph ( ua ph ) and neonatal death ( nd ) . the incidence of thyroid dysfunctions including hyperthyroidism or hypothyroidism was examined and compared among the groups of iugr , diabetes , hypertension , iufd , abruption , and thyroid disease .
data are expressed as number , incidence ( % ) , or mean  sd . probability values < 0.05 were considered significant .
in the 392 women , the mean gestational age at delivery was 34.3  6.3 weeks ( table 1 ) .
the incidence of thyroid dysfunction of each group is as follows : 31% in thyroid disease , 25% in iugr , 30% in diabetes , 27% in hypertension , 12% in iufd , and 7% in abruption ( table 2 ) .
the incidence of thyroid dysfunction was statistically insignificant in iugr , diabetes , ht , and abruption .
the group of thyroid disease accounted for only 10% of all thyroid dysfunctions ( figure 2 ) .
hypothyroidism was more prevalent than hyperthyroidism in the study groups except for the thyroid disease group .
26 cases of subclinical hyperthyroidism and 55 cases of subclinical hypothyroidism were found in the study groups ( table 2 ) .
the incidences of thyroid dysfunction in the diabetes ( 30% ) and thyroid disease ( 31% ) were slightly higher than those of other groups as previously reported [ 17 , 18 ] . on the other hand , the incidences of thyroid dysfunction in iugr ( 25% ) and hypertension ( 27% ) were also high .
besides , this study showed that the screening for women with thyroid disease ( symptoms of thyroid disease and personal history of thyroid disease ) could pick up only 10% of affected women .
in other words , it would miss 90% of affected women with thyroid dysfunction ( figure 1 ) .
therefore , current screening strategy for thyroid dysfunction during pregnancy is not sufficient . in our study , hypothyroidism was more prevalent than hyperthyroidism and most of cases ware categorized as subclinical disease ( table 2 ) .
in contrast to overt diseases , subclinical hypothyroidism and subclinical hyperthyroidism are not associated with poor pregnancy outcomes [ 19 , 20 ] . however , apart from preterm delivery or miscarriage , it was also reported that major obstetrical complications such as hypertension , iufd , or abruption were closely associated with subclinical hypothyroidism [ 2123 ] .
we also found that the incidence of thyroid dysfunction in the dm group was similar to the groups of thyroid disease , iugr , and hypertension .
high frequency of antithyroid antibodies in pregnant women with gestational diabetes mellitus was also reported .
acog and the endocrine society recommended that thyroid testing should be limited to women with symptoms of thyroid disease and those with a history of thyroid disease or other medical conditions associated with it , such as type 1 diabetes or autoimmune disorders [ 11 , 25 ] . according to our results , we recommended to screen thyroid function in women having the above - mentioned complications .
furthermore , three cases of overt hypothyroidism were noticed in the groups of dm and ht . we were not able to detect three cases of overt hypothyroidism , if thyroid testing was limited to women with thyroid disease .
one of the reasons was the trimester - specific range for tsh in this study .
mu / l . the normal range of tsh during pregnancy is narrow when compared to that of general population .
our perinatal center is a secondary hospital and mainly deals with referral cases due to thyroid disease , iugr , diabetes mellitus , hypertension , iufd , and placental abruption .
high hcg level at first trimester resulted in hcg - induced hyperthyroidism . in our study ,
first , the current study was done in one secondary hospital dealing with referral cases only . as a consequence
, there was a higher proportion of high - risk deliveries and a higher incidence of cesarean deliveries in our hospital .
a regional population - based study should be needed to verify the prevalence of thyroid dysfunction and the relevance of perinatal prognosis in low - risk population .
second , we did not investigate thyroid function of the child who was born from a mother with thyroid dysfunction .
the outcome of infant should be obtained to verify the effect of thyroid dysfunction during pregnancy .
the presence of antibodies influences clinical course of pregnancy independently from thyroid dysfunction . in conclusion
, we demonstrated that the prevalence of thyroid dysfunction is increased in pregnant women with obstetrical or medical complications . under the currently recommended screening method
, the majority of thyroid dysfunctions may be missing . with a full awareness of high incidence of thyroid dysfunction in pregnant women with obstetrical or medical complications
 
 objective . 
 we conducted the study to see the incidence of thyroid dysfunction in women with obstetrical high - risk factors . 
 methods . 
 we retrospectively reviewed medical charts of high - risk pregnant women who had examination for thyroid function during pregnancy . 
 women were divided according to clinical presentation , symptoms of thyroid disease and those with a personal history of thyroid disease ( thyroid disease , n = 32 ) , intrauterine growth restriction ( iugr , 
 n = 115 ) , diabetes mellitus ( diabetes , n = 115 ) , hypertension ( n = 63 ) , intrauterine fetal death ( iufd , n = 52 ) , and placental abruption ( abruption , n = 15 ) . the incidence of thyroid dysfunctions including hyperthyroidism or hypothyroidism was compared . 
 results . 
 the overall prevalence of thyroid dysfunction was 24.7% . 
 the incidence of thyroid dysfunction in each group was as follows : 31% in thyroid disease , 25% in iugr , 30% in diabetes , 27% in hypertension , 12% in iufd , and 7% in abruption . 
 except iufd , the incidence was not statistically significant from the group of thyroid disease ( thyroid disease versus iufd , p = 0.03 by 2 test ) . 
 thyroid disease represented for only 10% of all thyroid dysfunctions . 
 conclusion . 
 testing of women with a personal history or current symptoms of thyroid disease during pregnancy may be insufficient to detect women with thyroid dysfunction , who will become at high - risk pregnancy . 
1. Introduction
2. Materials and Methods
3. Results
4. Discussion