Accuracy of doppler assessment of the uterine arteries for the diagnosis of pubertal onset in girls: a scoping review

The uterine artery pulsatility index (PI) assessed by Doppler ultrasound reflects the impedance to the blood flow in the vessel distal to the sampling point. We aimed to assess the accuracy of the uterine artery PI for the diagnosis of puberty in girls. A PRISMA-ScR-compliant scoping review was performed in the MEDLINE and Embase databases with the search terms “puberty” and “Doppler ultrasonography”. Studies that included girls aged 0–18 years who underwent pelvic Doppler ultrasound with calculation of uterine artery PI were eligible. Ten studies comprising 1385 girls aged 1.2–18 years were included. The selected studies included participants from Italy, Brazil, Iran, Belgium and Denmark, and were published between 1996 and 2021. Six studies selected girls who were referred for evaluation of pubertal disorders, while four studies included only healthy girls. Nine studies found a significant difference in Doppler signal pattern and PI according to pubertal stage, with PI cutoff points ranging from 2.5 to 4.6 for the diagnosis of puberty, with a sensitivity of 77%–94%, specificity of 85%–100%, and accuracy of 79%–98%. Doppler assessment of the uterine arteries with PI calculation is a useful noninvasive tool in the diagnosis of pubertal onset in girls.

Puberty is a biological maturation process that represents the physical, hormonal, and psychological transition from childhood to adulthood 1 . In girls, the initial manifestation of puberty on physical examination is usually breast development (thelarche), with a normal age range of onset between 8 and 13 years 2 . Therefore, the classic definition of precocious sexual maturation is the development of secondary sexual characteristics before 8 years of age in girls 1 .
The initial laboratory evaluation of precocious sexual maturation in girls includes the measurement of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and estradiol 1 . The difficulties of hormonal assessment include the adequate and standardized determination of normal hormonal concentrations in healthy children, based on age and pubertal stage, for each laboratory method 3 . Additionally, there is a large overlap of estradiol values between pubertal and prepubertal girls 4 . The sensitivity of morning basal LH for the diagnosis of gonadotropin-dependent precocious puberty ranges from 56 to 100%, with a specificity of 64%-100%, depending on the cutoff point and assay used 3 . Therefore, gonadotropin-releasing hormone (GnRH) or long-acting GnRH agonist (GnRHa) stimulation tests are indicated in girls with a non-diagnostic basal LH 5 . The main disadvantages of the GnRHa stimulation test are its high cost, the unavailability of a short-acting GnRH in many countries, the waiting time between blood samples, and the risk of an injection-site reaction.
Pelvic ultrasound is a rapid, noninvasive, and low-cost method to assess uterine development and ovarian volume, with well-established utility in the investigation of pelvic pain, pelvic masses, and atypical genitalia 6 . Additionally, studies have definitively shown increased ovarian and uterine volume in girls with central precocious puberty (CPP) compared with prepubertal controls and girls with isolated premature thelarche (IPT) [7][8][9] . However, the sensitivity is low for differential diagnosis due to the large overlap of values between groups [10][11][12][13] . Doppler ultrasound allows the assessment of utero-ovarian blood flow and flow impedance measurement with the calculation of the pulsatility index (PI), defined as the difference between peak systolic flow and end-diastolic flow divided by the mean flow velocity 14 . The presence of estrogen receptors in the walls of the uterine arteries, which promote a reduction in vascular resistance when there is hormonal stimulation, appears to be responsible for www.nature.com/scientificreports/ changes in the vascular flow pattern 15,16 . Color Doppler-based studies for the evaluation of female reproductive disorders have highlighted the public health relevance of this safe, efficient, and affordable diagnostic modality 17 . Within this context, the present study was designed to evaluate the accuracy of the uterine artery PI for the diagnosis of puberty in healthy girls and girls with signs of sexual precocity by means of a scoping review of the literature.

Methods
Protocol and registration. This scoping review follows the recommendations of the PRISMA Extension for Scoping Reviews (PRISMA-ScR) protocol 18 . The final protocol was registered prospectively with the Open Science Framework on 15 September 2021 19 . Eligibility criteria. We included studies that evaluated the accuracy of Doppler ultrasound with uterine artery PI in girls aged 0 to 18 years for the diagnosis of pubertal onset. The exclusion criteria were studies including pregnant women and review studies. There was no language or date restriction; articles written in languages other than English, Portuguese, and Spanish were considered eligible if they contained sufficient English-language information in the abstract, tables, and figures. Selection of sources of evidence. Two independent reviewers (A.V.C. and C.M.) assessed records for inclusion based on titles and abstracts. Abstracts that did not meet the inclusion criteria or that met the exclusion criteria were discarded. The remaining records and those whose abstracts did not provide sufficient information to decide upon their exclusion were selected for full-text evaluation, which was performed by the same reviewers independently. A third reviewer (S.P.S.) solved any disagreements.
Data charting process and data items. Two investigators (A.V.C. and C.M.) analyzed the selected studies and extracted data using a standardized system designed for this study. The following information was obtained: first author, year of publication, study design, sample size, inclusion and exclusion criteria, reference method for diagnosis of puberty, age and pubertal stage distribution, PI cutoff point, diagnostic accuracy measures of the index test (sensitivity, specificity, correlation, accuracy, and positive and negative predictive values).

Synthesis of results.
We summarized the information extracted from the included studies in tables.

Ethics approval. The study protocol was approved by the Hospital de Clínicas de Porto Alegre Research
Ethics Committee (GPPG number 2021-0290).

Results
The search strategy identified 272 citations, of which 235 remained after removal of duplicates. We excluded 218 articles after title and abstract screening, leaving 17 studies for full-text evaluation. Finally, 10 studies including 1385 participants were selected for the scoping review. Figure 1 shows the PRISMA flow diagram.
The selected articles were published between 1996 and 2021 and included girls from five countries (Italy, Brazil, Iran, Belgium, and Denmark). Six studies were cross-sectional in design [20][21][22][23][24][25] and four were prospective [26][27][28][29] . The ages of the participants ranged from 1.2 to 18 years. The majority of the studies (n = 6) included girls who were referred for evaluation of pubertal disorders, mainly thelarche or pubarche before 8 years of age. Four articles selected healthy girls 20,23,25,29 . Ultrasound examination was reported to be performed by the same radiologist in seven studies 20,21,24-28 , four of which were highly experienced 20,21,24,28 . The main characteristics of the studies are shown in Table 1.
Among the ten included articles, nine found a significant difference in Doppler and PI according to pubertal stage, with PI cutoff points ranging from 2.5 to 4.6 for the diagnosis of puberty onset, with a sensitivity of 77%-94%, specificity of 85%-100% and accuracy of 79%-97%. Figure 2 shows the sensitivity and specificity of the PI for the diagnosis of pubertal onset. Table 2 provides a summary of these results.

Discussion
We performed a scoping review to map the existing literature and to synthesize research evidence about Doppler ultrasound of the uterine arteries for the diagnosis of puberty in girls. Ten articles examined this method in a population of healthy girls at different pubertal stages or those with signs of sexual precocity. Five studies showed that uterine artery PI detected puberty onset with a high accuracy. Additionally, the overwhelming majority of the studies described significant changes in the pattern of uterine artery flow with the progression of puberty. Only one article did not find Doppler ultrasound useful in this setting.
The size and morphology of the uterus and ovaries are relatively stable during childhood, and the uterine fundus and cervix have a similar width 30 . During puberty, the uterus increases progressively in size, becoming wider than the cervix, ovarian volume also increases, and multiple cysts can be seen during each menstrual cycle 31,32 . Ovarian volume and the quantity of large follicles are generally inferior markers of puberty onset compared with uterine parameters 11,33 . On the other hand, a recent systematic review and meta-analysis of 13 studies found that girls with CPP had significantly greater uterine and ovarian measurements, and a uterine length greater than 3.20 cm was a reliable marker to differentiate CPP from IPT with a diagnostic odds ratio of 19.62 and an area under the curve of 0.820 34 . However, the PI was not evaluated in this meta-analysis. Based on the studies identified in our scoping review, the vascular flow pattern in the uterine arteries changes with the growing uterus during pubertal development. There is a decline in vascular resistance with the onset of puberty, expressed by the significantly lower PI at this stage, and finally, a further increase in impedance at the end of puberty, probably by complete uterine angiogenesis.
The cutoff point for uterine artery PI to identify the onset of puberty varies between 2.5 and 5.0 in the literature. This can be explained by differences in the inclusion criteria across studies (only healthy girls vs. girls with physiological puberty or precocious puberty) and by the different reference tests used for defining pubertal onset. Furthermore, the ultrasound examination is operator-dependent, and its outcome can be influenced by the experience of the radiologist. Four studies mention that an experienced radiologist performed the examinations, and in only two articles were the intra-or interobserver variability of the PI measures assessed 20,21 . Finally, the cutoff point is generally given by the optimal cut-point when equal weight is given to sensitivity and specificity 35 . In clinical practice, a higher sensitivity of the PI may be more important for the evaluation of a girl with a suspected pubertal disorder.
Several factors, such as genetics, epigenetics, and lifestyle, are implicated in the onset and completion of puberty 36 . The age at puberty onset varies greatly between different ethnic populations 37 . Studies in the United States using data from the Third National Health and Nutrition Examination Survey showed that non-Hispanic black girls on average enter puberty first, followed by Mexican American and then non-Hispanic white girls, and non-Hispanic black girls had menarche at a substantially younger age 38,39 . Socioeconomic inequalities might also account for important variations in the timing of puberty within and among countries 40 . As an example, in some Asian, African, and South American countries, girls living in privileged conditions also show differences in average menarcheal age as compared with those living in underprivileged conditions 40 . Our scoping review included studies from five countries: three developed economies in Europe, one developing country in Latin America, and one developing country on the Asian continent. Overall, our results showed that Doppler ultrasound performs well in girls of different backgrounds. Due to the well-recognized distinct ethnic and socioeconomic influences on pubertal development, it is important to investigate the accuracy of Doppler ultrasound in each population. In studies that included healthy girls, the mean age of girls with a Tanner breast score of 2 was 9.7 years in the  www.nature.com/scientificreports/ Tanner breast score 1 (n = 24), Tanner breast score 2 (n = 10), Tanner breast score 3 (n = 11), Tanner breast score 4 (n = 1), Tanner breast score 5 (n = 12), Tanner score not evaluated ( 25 , that of initial puberty was 10.8 in the Iranian study 23 , that of girls in physiological puberty was 10.5 years in the most recent Italian study 21 , and that of thelarche was 10.2 years in the Brazilian study 20 . Some limitations of our scoping review must be taken into account. First, the studied population is heterogeneous in relation to both the presence and absence of signs of sexual precocity as well as in the average age of the participants. Nevertheless, scoping reviews are of particular use when a body of literature exhibits a large, complex, or heterogeneous nature not amenable to a more precise systematic review 41 . Second, the sample comprises girls from only five countries, which limits the external validity of the findings. However, the value of scoping reviews in evidence-based practice is the examination of a broader area to identify gaps in the research knowledge base 42 . Third, only five studies reported measures of diagnostic accuracy of the PI. These limitations notwithstanding, we believe we were able to effectively find and summarize the current evidence on the accuracy of uterine artery evaluation in girls.
In conclusion, Doppler assessment of the uterine arteries with PI calculation is a useful noninvasive tool in the differential diagnosis of secondary sexual characteristic onset in girls. Therefore, this parameter should be considered in the diagnostic approach to pubertal disorders, further reinforcing the need for new dynamic collaborations in the development of precision-medicine models. Given the paucity of data on a broader population, future studies following the guidelines for validation of diagnostic methods should be conducted to evaluate the uterine artery PI in girls at different ages and pubertal stages.   In post-menarche girls, the PI correlated significantly with increasing years after menarche