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Heart rate variability (HRV) can sensitively reflect autonomic balance, but HRV data in SCH during pregnancy remain limited. This study compared HRV between newly diagnosed SCH and euthyroid controls in the second trimester using resting ECG analysis, evaluating time-, frequency-, and nonlinear indices.",{"@graph":69,"@context":127},[70,84,106],{"@type":71,"itemListElement":72},"BreadcrumbList",[73,77,79,82],{"item":74,"name":75,"@type":76,"position":8},"https://docshare.wps.com","Home","ListItem",{"item":78,"name":9,"@type":76,"position":14},"https://docshare.wps.com/document/",{"item":80,"name":35,"@type":76,"position":81},"https://docshare.wps.com/document/healthcare/",3,{"item":83,"name":65,"@type":76,"position":19},"https://docshare.wps.com/document/comparative-evaluation-of-thyroid-profiles-and-heart-rate-variability-in-newly-diagnosed-subclinical-hypothyroid-and-euthyroid-pregnant-women/413038/",{"url":83,"name":65,"@type":85,"image":86,"author":91,"headline":65,"publisher":94,"fileFormat":97,"inLanguage":63,"description":67,"dateModified":98,"datePublished":99,"encodingFormat":97,"isAccessibleForFree":100,"interactionStatistic":101},"DigitalDocument",{"url":87,"@type":88,"width":89,"height":90},"https://docshare.wps.com/thumbnails/comparative-evaluation-of-thyroid-profiles-and-heart-rate-variability-in-newly-diagnosed-subclinical-hypothyroid-and-euthyroid-pregnant-women/413038.png","ImageObject",300,407,{"name":92,"@type":93},"WPS_1790064749","Person",{"url":74,"name":95,"@type":96},"DocShare","Organization","application/pdf","2026-10-31","2026-09-28",true,{"@type":102,"interactionType":103,"userInteractionCount":105},"InteractionCounter",{"@type":104},"ViewAction",12,{"@type":107,"mainEntity":108},"FAQPage",[109,115,119,123],{"name":110,"@type":111,"acceptedAnswer":112},"What was the main objective of the study?","Question",{"text":113,"@type":114},"To evaluate how HRV differs between pregnant women with newly diagnosed subclinical hypothyroidism and euthyroid pregnant controls in the second trimester.","Answer",{"name":116,"@type":111,"acceptedAnswer":117},"How were HRV measurements obtained and analyzed?",{"text":118,"@type":114},"Resting five-minute Lead II ECGs were recorded and analyzed for HRV using LabChart Pro v8.1.30, assessing frequency-, time-, and nonlinear-domain indices.",{"name":120,"@type":111,"acceptedAnswer":121},"Which HRV findings were significantly different in subclinical hypothyroidism?",{"text":122,"@type":114},"SCH showed lower time-domain parameters (SDNN, RMSSD, pNN50), higher LF in the frequency domain, reduced total power, and reduced nonlinear indices (SD1, SD2), while other measures such as LF/HF ratio and SD1/SD2 remained comparable.",{"name":124,"@type":111,"acceptedAnswer":125},"Was thyroid-stimulating hormone (TSH) associated with HRV indices?",{"text":126,"@type":114},"Correlation analysis found no significant association between TSH and HRV indices (all p>0.05).","https://schema.org",{"og:url":83,"og:type":129,"og:title":65,"og:site_name":95,"og:description":67},"article",{"robots":131,"canonical":83},"index,follow",{"doc_id":133,"site_id":62},413038,1790904648,{"code":4,"msg":5,"data":136},{"doc_id":133,"user_id":137,"nickname":92,"user_avatar":138,"doc_module":4,"category_id":34,"category_name":35,"doc_title":65,"doc_description":67,"doc_content":139,"file_id":140,"file_url":141,"file_type":142,"file_size":143,"view_count":105,"is_deleted":4,"is_public":8,"is_downloadable":8,"audit_status":8,"page_count":39,"language":144,"language_code":63,"site_id":62,"html_lang":63,"table_of_contents":145,"faqs":146,"seo_title":147,"seo_description":67,"update_tm":148,"read_time":46,"preview_page_count":4},3985747859154,"https://ap-avatar.wpscdn.com/davatar_276721f389ce27ea32af1340a28f341c","Review began 11/08/2025  \nReview ended 11/25/2025  \nPublished 12/02/2025  \n© Copyright 2025  \nSingh et al. This is an open access article distributed under the terms of the Creative Commons Attribution License CC-BY 4.0. , which permits unrestricted use , distribution , and reproduction in any medium , provided the original author and source are credited.  \nDOI: 10.7759/cureus.98316  \nOpen Access Original Article  \nComparative Evaluation of Thyroid Profiles and Heart Rate Variability in Newly Diagnosed Subclinical Hypothyroid and Euthyroid Pregnant Women  \nAnchal Singh 1, Samir K. Singh 1, Hanjabam Barun Sharma 1, Mamta Singh 2  \n1. Physiology, Institute of Medical Sciences, Banaras Hindu University, Varanasi, IND 2. Obstetrics and Gynaecology, Institute of Medical Sciences, Banaras Hindu University, Varanasi, IND  \nCorresponding author: Samir K. Singh, [drskss01@gmail.com](drskss01@gmail.com)  \nAbstract  \nBackground  \nSubclinical hypothyroidism (SCH) is a common pregnancy condition that is frequently regarded as a biochemical finding with few functional implications. Thyroid hormones, however, have an impact on autonomic modulation, and even slight insufficiencies can change a mother 's cardiovascular flexibility. Although heart rate variability (HRV) is a sensitive indicator of autonomic balance, there is little information available on HRV in pregnant women with SCH.  \nMethods  \nAn analytical observational study was carried out on 41 pregnant women with recently diagnosed SCH and 40 pregnant controls who were euthyroid and in their second trimester. Lead II configuration resting fiveminute ECGs were captured. LabChart Pro v8.1.30 software (AD Instruments, Castle Hill, Australia) was used to analyze them for HRV. Measurements were made in the frequency domain (low frequency (LF), high frequency (HF), LF/HF ratio, and total power), time domain (average duration of all normal-to-normal (NN) intervals between consecutive heartbeats (mean RR), standard deviation of normal-to-normal intervals (SDNN), root mean square of the standard deviation of interbeat intervals (RMSSD), and percentage of interbeat intervals varying by more than 50 ms (pNN50)), and nonlinear indices (standard deviation of the instantaneous beat-to-beat variability (SD1), standard deviation of the continuous long-term variability of RR intervals (SD2), and index of the balance between short-term and long-term variability (SD1/SD2)) . With significance set at p\u003C0 .05, statistical analysis was conducted using either the Mann-Whitney U test or the unpaired t-test, depending on the distribution of the data.  \nResults  \nMean RR was comparable between groups (p=0 .331) . Time-domain parameters were significantly lower in SCH: SDNN (p=0 .005), RMSSD (p=0 .035), and pNN50 (p=0 .026) . In the frequency domain, LF was significantly higher in SCH (p=0 .04), whereas HF (p=0 .281) and LF/HF ratio (p=0 . 143) were comparable. Total power was significantly reduced in SCH (p=0 .0001) . Nonlinear indices also showed reductions in SD1 (p=0 .009) and SD2 (p=0 .0001), while SD1/SD2 ratio remained comparable (p=0 .585) . Correlation analysis revealed no significant association between thyroid-stimulating hormone (TSH) and HRV indices (all p>0 .05) .  \nConclusion  \nSubclinical hypothyroidism in pregnancy, though biochemically mild, is associated with early autonomic dysfunction characterized by reduced parasympathetic activity and diminished global HRV. These changes occur even in the absence of alterations in basal heart rate, suggesting subtle but functionally relevant cardiovascular impairment. HRV analysis may serve as a sensitive non-invasive tool for detecting early autonomic dysregulation in SCH and highlights the need for closer maternal surveillance during pregnancy.  \nCategories: Other, Obstetrics/Gynecology, Endocrinology/Diabetes/Metabolism  \nKeywords: autonomic regulation, heart rate variability, pregnancy, second trimester, subclinical hypothyroidism  \nIntroduction  \nT","cbCaijIrI4CjZKyj","https://ap.wps.com/l/cbCaijIrI4CjZKyj","pdf",155956,"English","# Abstract\n## Background\n## Methods\n## Results\n## Conclusion\n# Introduction\n# How to cite this article","[{\"question\":\"What was the main objective of the study?\",\"answer\":\"To evaluate how HRV differs between pregnant women with newly diagnosed subclinical hypothyroidism and euthyroid pregnant controls in the second trimester.\"},{\"question\":\"How were HRV measurements obtained and analyzed?\",\"answer\":\"Resting five-minute Lead II ECGs were recorded and analyzed for HRV using LabChart Pro v8.1.30, assessing frequency-, time-, and nonlinear-domain indices.\"},{\"question\":\"Which HRV findings were significantly different in subclinical hypothyroidism?\",\"answer\":\"SCH showed lower time-domain parameters (SDNN, RMSSD, pNN50), higher LF in the frequency domain, reduced total power, and reduced nonlinear indices (SD1, SD2), while other measures such as LF/HF ratio and SD1/SD2 remained comparable.\"},{\"question\":\"Was thyroid-stimulating hormone (TSH) associated with HRV indices?\",\"answer\":\"Correlation analysis found no significant association between TSH and HRV indices (all p\\u003e0.05).\"}]","Comparative Evaluation of Thyroid Profiles and Heart Rate Variability in Newly Diagnosed Subclinical Hypothyroid and Euthyroid Pregnant Women | PDF",1790593606]