the majority of thyroid cancers are classified as papillary ( 88% ) or follicular ( 9% ) ; together these two histological types are grouped as differentiated thyroid cancers ( dtc ) . while the annual rate of cancer incidence is decreasing , there has been a 2.4-fold increase in thyroid cancer from 1973 to 2002 . dtc occurs more commonly in women of child - bearing age with an incidence of 14 per 100,000 live births and represents the second most frequent tumor diagnosed during pregnancy only behind breast cancer [ 7 , 8 ] .   as dtc is commonly found during pregnancy or in the early postpartum period , it is possible that physiological changes associated with it , as high levels of estrogen , human chorionic gonadotropin ( hcg ) and/or others , could create a favorable environment to tumor development and growth . maternal thyroid gland secretes more thyroid hormone during early pregnancy in response to the thyrotropic activity of hcg that overrides the operation of the hypothalamic - pituitary - thyroid feedback system . this could partially explain an increase in the size of preexisting thyroid nodules as well as new thyroid nodule formation in pregnancy [ 1015 ] . the best treatment option for thyroid cancer in pregnant women or in the early postpartum period should be based on evidence , so the aim of this paper was to evaluate whether the prognosis of dtc associated with pregnancy is similar or not to dtc in nonpregnant women . this literature search was conducted in the pubmed , cochrane , and scopus databases , combining the mesh terms : thyroid neoplasms and pregnancy . all studies in english until february 2011 were included . to be included in this review the original article should describe the comparison between the outcomes in patients diagnosed with dtc during pregnancy or in the first 12 months postpartum ( dtc related to pregnancy ) , with a control group comprising women of child - bearing age , diagnosed with dtc when nonpregnant or at least 12 months after delivery . all citations and abstracts identified by the electronic search were reviewed by two independent reviewers . after reviewing 398 abstracts from the electronic search and 3 summaries obtained by manual search , 54 articles were reviewed in full - text form . however , after analysis of these studies , several were excluded , for the following reasons : dtc did not occur during pregnancy , there was no control group , there was no reporting of outcomes , or they described small case series , so only four studies were included in this paper , as shown in figure 1 [ 14 ] . the characteristics of the studies and the outcomes are described , respectively , in tables 1 and 2 . as dtc has a good prognosis , the number of patients studied should be large , and the followup should be very long to detect any difference in survival or even recurrence . most recurrences of dtc occur within the first five years after initial treatment , but recurrences may occur many years or even decades later , particularly in patients with papillary cancer [ 16 , 17 ] . in addition to this , decisions about cancer treatment during pregnancy are associated with ethical conflicts between the best option for the mother and for the fetus [ 18 , 19 ] . the management of pregnant women with cancer should consider the maternal - fetal risk related to treatment , as well as the possibility of tumor progression for postponing treatment or for the tumor being related to pregnancy . during this study we could observe that there is little published data comparing outcomes in patients with dtc related to pregnancy or not . no randomized controlled trial was available . in the study of moosa and mazzaferri there was no impact from pregnancy in dtc - related death ; in the studies of yasmeen et al . and herzon et al . overall survival was not affected by dtc [ 2 , 4 ] ; when evaluating if the timing of surgical treatment , during pregnancy or after birth , affected the prognosis of patients with dtc detected during pregnancy , moosa and mazzaferri and yasmeen et al . [ 2 , 3 ] have not shown differences in recurrence rates and , respectively , in dtc - related death and overall survival . such findings , however , are not in agreement with the study published by vannucchi et al . they   found a strong association of dtc in pregnant women with recurrence or persistence of cancer ( 60% in pregnant women ( group 2 ) versus 4.2% in women with dtc diagnosed 1 year after delivery ( group 1 ) versus 13.1% in nulliparous patients when diagnosed with dtc ( group 3 ) ) . after a stepwise logistic regression analysis entering the following variables : extrathyroidal extension , lymph - node metastases , radioiodine treatment , pregnant or not pregnant status at diagnosis , histotype , and tumor size 2 or > 2  cm , pregnancy was found to be the most significant predictor for disease recurrence or persistence . as the outcomes and the methodology employed in each study were different , it was not possible to compare their results and to combine the data in a meta - analysis . in the studies of yasmeen et al . and herzon et al . , the overall survival was the main outcome [ 2 , 4 ] , while the study of moosa and mazzaferri had death related to dtc and recurrence , evaluated by biopsy or by i uptake in distant sites , as primary outcomes , and the more recent study of vannucchi et al . evaluated persistent / recurrent dtc through more sensible tests such as tg basal levels and tg response to rhtsh . such methods were not used in the study of moosa and mazzaferri , which could explain some of the discrepancies among them .   in the study of vannucchi et al . however , this factor does not seem to explain the worse outcome which has been found on the group of patients with dtc associated to pregnancy , since two of three patients with follicular histology remained in remission . two studies reported differences among clinical presentation between pregnant and nonpregnant women [ 1 , 3 ] . in the study of moosa and mazzaferri , fewer pregnant patients showed symptoms associated to thyroid nodules ( 74% versus 43% , p < 0.01 ) . on the other hand , in the study of vannucchi et al . dtc was less commonly an incidental finding in pregnant patients , probably indicating that these patients had more aggressive disease . the expression of the estrogen receptor alfa through immunohistochemical analysis was higher in group 2 patients , as compared to groups 1 and 3 . as estrogen probably increases proliferative activity of thyroid follicular cells , this hormone could be implicated in a more aggressive pattern of dtc diagnosed in pregnancy . other important factor found in this paper refers to the time of followup of the studies . considering that dtc is a disease with low lethality and the followup was not very long , it is possible that the full impact of dtc on the patients survival was not evident . the central lymphadenectomy ( vi - vii levels ) was performed on all patients in the cohort described by vannucchi et al . , and , according to clinical judgment , in the other studies [ 24 ] . there seemed to be no difference on the outcome of dtc during pregnancy whether the surgery took place at the second trimester of pregnancy or after childbirth [ 24 ] . in contrast to these findings , kuy et al . compared the risk of thyroid and parathyroid surgery complications in pregnant and nonpregnant women , paired by age , in a retrospective cross - sectional study . a total of 201 pregnant women and 31155 nonpregnant women were included ; among the 201 pregnant women , 45.8% have undergone surgery due to thyroid cancer , the others had benign thyroid and parathyroid diseases . thyroidectomy during pregnancy was associated with an increased surgical complication rate in both malignant ( 21% to 8% ) and benign diseases ( 27% to 14% ) , as well as higher endocrine complication rates ( 15.9% to 8.2% ) and treatment costs ( $ 6873 versus $ 5963 ) .   in summary , there are few studies which give base to the policies about pregnant patients with dtc . up to present time , data obtained through systematic review show conflicting results when it comes to observed outcomes in this population . there seem to be a higher disease recurrence and persistence rates in this population when current treatment response evaluation methods are employed . however , the impact on overall survival in the long time appears to be unaltered . there is no evidence to support termination of pregnancy when the diagnosis of dtc is performed . the guidelines of the endocrine society for pregnancy - related dtc recommend thyroidectomy after delivery for patients with no evidence of advanced disease or without rapid progression , and thyroidectomy in the second trimester of pregnancy for the others ( uspstf recommendation level b ) . prospective studies should be done to compare the prognosis of dtc diagnosed during pregnancy or not , as well as the effects of postponing surgery after childbirth in dtc diagnosed during pregnancy .