Central precocious puberty (CPP) is among the most common endocrine disorders in girls but is rare in boys. It is defined by premature activation of the hypothalamic-pituitary-gonadal axis before age 8 years in girls and 9 years in boys. Early secondary sexual development and accelerated skeletal maturation may result in psychosocial difficulties and compromised adult height [1-3]. A recent systematic review has also demonstrated that CPP may increase the risk of early menopause, breast cancer, obesity, and cardiovascular disease [4]. Beyond these clinical impacts, CPP also imposes a substantial economic burden. Affected children incur healthcare costs that are approximately 6–12 times higher than those of their unaffected peers, largely attributable to CPP itself and its associated comorbidities [5]. Accordingly, national epidemiologic data are essential to quantify disease burden, enable cross-regional comparisons, and inform healthcare planning, resource allocation, and prevention strategies.

A recent systematic review of global CPP epidemiology data demonstrated marked heterogeneity across countries and socioeconomic settings, with a pooled prevalence of ~7.9% in girls and ~4.0% in boys [6]. Prevalence was highest in Asian populations and in low- and upper-middle-income countries. However, incidence data remain limited and are derived predominantly from high-income settings [6]. Across 9 studies from 7 countries (South Korea [7], Denmark [8], Taiwan [9], France [10], Spain [11], Italy [12], and Puerto Rico [13]), incidence ranged from 1.1 to 489 per 100,000 girls and 0.1 to 22.4 per 100,000 boys, highlighting substantial variation across settings [6]. A few longitudinal data also consistently demonstrate increasing CPP incidence over time [7,8,14,15], in parallel with a global shift toward earlier pubertal onset [16]. Among these, South Korea has shown the most pronounced rise, with incidence in girls increasing from 89 to 1,415 per 100,000 between 2008 and 2020 [7]. This trend was further accentuated during the coronavirus disease 2019 (COVID-19) pandemic, with multiple reports demonstrating a surge in CPP diagnoses [17]. However, postpandemic trends remain unclear, and only few studies have evaluated the incidence trend across pre-, during, and postpandemic trajectory within a single national cohort [14,15,18]. Nationwide incidence data from Southeast Asia, including Thailand, remain lacking despite the region’s potential contribution to the global burden. In addition, epidemiologic data on premature thelarche (PT), a common benign pubertal variant that overlaps clinically with CPP, are scarce and rarely evaluated alongside CPP. Therefore, we conducted a nationwide population-based study to examine temporal trends in the incidence of CPP and PT among Thai children from 2018 to 2024, across the COVID-19 periods.

This nationwide study used Thailand’s primary healthcare claims database (2018–2024) to examine the incidence of CPP and PT in children. Our results demonstrated that CPP incidence in Thai children (15–51.7 per 100,000 person-years) was lower than that reported in other Asian countries but generally higher than earlier reports from Europe. As expected, incidence was markedly higher in girls than boys. In girls, CPP incidence increased during the COVID-19 pandemic and remained elevated thereafter, with the greatest rise in peripubertal age groups, whereas incidence in boys remained stable. PT incidence in girls increased steadily throughout the study period. Collectively, these findings provide important evidence to inform healthcare and resource planning, while contributing to the global understanding of CPP epidemiology.

Our study found that both the contemporary incidence and the rate of increase of CPP in Thai girls were lower than those reported in higher-income Asian countries [7,9]. In South Korea, incidence during 2004–2010 was comparable to our findings [22], but subsequently rose sharply to 1,415 per 100,000 person-years by 2020 [7], far exceeding the peak observed in our study. In Taiwan, incidence during 2002–2013 already exceeded that of South Korea and likely continued to rise [9]. Differences between Thailand and these East Asian countries may partly reflect genetic background, as Korean and Taiwanese populations share East Asian ancestry distinct from the Thai population [23,24]. Environmental and lifestyle factors, such as the rising prevalence of obesity [25] and greater exposure to endocrine-disrupting chemicals, may also contribute to higher CPP incidence [26]. Compared with Western countries, CPP incidence in our study was higher than earlier reports from Mediterranean Europe (1997–2013; 0.1–26.8 per 100,000 girls), including France, Italy, and Spain [10-12]. However, these estimates were generated up to 2 decades ago and should be interpreted in the context of a global upward trend. In contrast, Denmark has consistently reported higher incidence, increasing from 26 per 100,000 person-years in 1998 to 146 in 2017 [8]. Beyond biological and environmental factors, cross-country differences may also be influenced by variation in case definitions, referral pathways, and registry completeness, with countries such as Denmark and South Korea having highly comprehensive national health registries [27,28].

Compared with the sensitivity analysis using the conventional age cutoff (<8 years), the primary analysis utilizing the extended cutoff (<9 years) yielded higher AIRs of CPP in girls while temporal trends remained unchanged. This pattern is in line with Korean [7] and Danish [8] claims-based studies, where broader age criteria produced higher incidence estimates. However, unlike those studies which utilized clinical data [8] or GnRHa prescription records [7] to support CPP ascertainment, our dataset lacked such information. Consequently, our findings warrant cautious interpretation, as the inclusion of girls aged 8–<9 years may have captured some children with early or rapidly progressive puberty rather than definite CPP.

During the COVID-19 pandemic, a marked increase in CPP incidence was observed, reaching an approximately 2.3-fold peak. This finding is congruent with a meta-analysis showing an approximately twofold increase in the odds of precocious puberty during the pandemic [17]. Lockdowns and school closures were associated with increased caloric intake, reduced physical activity, greater psychosocial stress, and increased screen time, all of which are associated with obesity and accelerated pubertal progression [29]. However, data on CPP epidemiology in the postpandemic period remain limited. While a single-center study from the United States demonstrated a decline in CPP cases after the pandemic [18], our results, together with data from Japan and Turkey, showed persistently elevated incidence [14,15]. This finding may be attributable to persistent lifestyle changes adopted during the pandemic [3] or sustained increases in childhood obesity [30]. However, because CPP incidence had already increased during the prepandemic period, the persistently elevated postpandemic incidence may also reflect continuation of a preexisting upward trend. Future studies with longer prepandemic and postpandemic observation periods are needed to distinguish pandemic-related effects from underlying secular trends.

In age-stratified analyses, the largest increase in CPP incidence during the peak of the COVID-19 pandemic occurred in girls aged 4–<9 years, particularly those aged 8–<9 years. After the peak, incidence appeared to decline slightly across age groups, though changes were not statistically significant. In contrast, incidence remained stable in girls aged 0–<4 years. These patterns are consistent with data from South Korea and Denmark, which showed greater increases among peripubertal-aged girls, particularly around age 8 years [7,8]. Together, these findings suggest that environmental factors may preferentially accelerate pubertal onset during the peripubertal window.

To date, few studies have examined PT epidemiology. In our study, PT incidence in Thai girls increased gradually over time, with a smaller rise than CPP, reaching approximately twofold above baseline by 2024. Our incidence was substantially lower than that reported in Danish and Swedish populations [8,31]. In age-stratified analyses, the increase was greatest in older girls aged 7–<8 years, paralleling CPP patterns but at lower rates. PT occurring at atypical ages (>2 years) has been recognized as a potential precursor of early normal puberty or CPP [32]. Among younger girls aged <2 years, incidence also increased, particularly postpandemic.

The overall increase in PT and CPP incidence in our study is consistent with global trends and parallels the secular shift toward earlier pubertal onset worldwide [16]. In Thailand, previous studies have demonstrated declines in age at thelarche of ~1–2 months per decade and in age at menarche of 2–5 months per decade [33,34]. These findings raise ongoing debate regarding whether current age cutoffs for thelarche should be reconsidered, as several studies found no adverse impact on final height in girls entering puberty at 7–8 years [35]. The introduction of fully subsidized quarterly GnRHa therapy in Thailand in 2019 may have improved treatment accessibility and reduced financial barriers, potentially increasing healthcare-seeking behavior, referral to pediatric endocrinology services, and case detection. Greater availability of treatment may also have increased awareness of CPP among clinicians and families. Additionally, obesity among Thai children continued to rise across the COVID-19 period, which may have further contributed to CPP risk [30].

Nationwide data on CPP incidence in boys are limited and less up-to-date than in girls. Our study found that CPP incidence in Thai boys was substantially lower than that reported in recent studies from other countries, approximately 4-, 10-, and 100-fold lower than rates observed in Turkey [14], Denmark [8], and South Korea [7], respectively. Our estimates were also lower than those from earlier studies conducted during 2000–2013 [8-10]. While several studies demonstrated a significant increase in CPP incidence in boys during the COVID-19 pandemic [14,15], we observed a relatively stable incidence over the same period. Given the small number of male cases and the resulting wide CIs, these findings in boys should be regarded as exploratory. The lower incidence in Thai boys, together with the absence of a pandemic-related increase, may reflect underdiagnosis rather than true biological differences. Testicular enlargement is less apparent than breast development in girls and requires clinical examination, contributing to underrecognition. Limited parental awareness may further delay detection, as early changes are often unnoticed until more advanced Tanner stages. These findings suggest the need to improve awareness to enhance case detection in boys in Thailand.

In conclusion, CPP incidence in Thai girls increased during COVID-19 and remained elevated thereafter, while PT incidence rose gradually. These trends were most pronounced among peripubertal-aged girls and may reflect pandemic-related changes in obesity, lifestyle, awareness, or a possible shift toward earlier pubertal onset. Further longitudinal studies incorporating clinical, anthropometric, and lifestyle data are needed to better understand the factors associated with these trends and their clinical implications.

This study has several limitations. First, the NHSO database lacks clinical, laboratory, radiographic, and GnRHa prescription data; therefore, CPP diagnoses could not be validated against national diagnostic criteria. Although repeated ICD-10-TM coding with a minimum 6-month follow-up period and systematic exclusion of peripheral causes were used to improve case ascertainment and diagnostic specificity, these approaches do not confirm the clinical diagnosis of CPP at the individual level. Accordingly, this study should be interpreted as estimating trends in administratively coded CPP diagnoses, rather than clinically confirmed CPP. Moreover, extending the age definition by 1 year may have included some cases of early puberty or a fast pubertal tempo rather than true CPP, potentially leading to overestimation of incidence. Therefore, the AIR results should be interpreted with caution. Nevertheless, the temporal trends were consistent between the main and sensitivity analyses, supporting the robustness of the observed trend. Second, misclassification for CPP and PT due to reliance on ICD-10-TM coding remains possible. Third, the analysis was restricted to children insured under the UCS and did not include those covered by other insurance schemes, who may differ in socioeconomic background, healthcare-seeking behavior, access to pediatric endocrine services, and referral patterns. Although the UCS covers approximately 72% of Thai children and provides broad nationwide representation, the incidence estimates should be interpreted as reflecting the UCS-insured pediatric population rather than all Thai children. Caution is therefore warranted when generalizing these findings to uninsured groups, privately insured populations, or health systems outside Thailand. Fourth, key individual-level factors, including body mass index, physical activity, screen time, psychosocial stress, and socioeconomic status, were unavailable, limiting mechanistic inference. Finally, the relatively short observation period precludes definitive conclusions on whether the postpandemic elevation reflects a sustained secular trend or a transient effect.