Assessing Clinical Embryology Research: A Global Bibliometric Analysis

Background and Objectives: The evaluative strength of available bibliometric tools in the field of clinical embryology has never been examined in the literature. The aim is to bring insight regarding the identity of clinical embryology research, introducing concerns when solely relying on the methodology of bibliometric analysis. Materials and Methods: An all-inclusive analysis of the most bibliometrically highlighted scientific contributions regarding the cornerstones of clinical embryology was performed employing the Scopus, Web of Science (WoS) and PubMed databases, between 1978–2018. An analysis of the number of publications, respective citations and h-index, g-index, along with m-quotient is presented. The top 30 contributing authors for each distinctive area of research are listed. An attempt at visualizing the yearly published articles, clusters, and collaborations of authors, along with the geographic origin of publications, is also presented. Results: Combining all searches and keywords yielded 54,522 results. In the Scopus database, employing the keyword “In Vitro Fertilization” yielded 41,292 results. The publications of the top five authors in each research field were analytically presented and compared to the total number of publications for each respective field. The research field of Preimplantation Genetic Diagnosis/Screening/Testing was allocated the highest percentage of publications produced by the top five authors. Regarding journal bibliometrics, based on the year 2017 metrics, there are only 29 journals according to WoS that refer to “Reproductive Biology”, ranking it 187th among 235 disciplines. The USA produced the highest number of publications (12,537). Conclusion: Results indicate an explosion of interest published in the literature regarding the field of clinical embryology. Further analysis on collaborations and the trends involved should be of added value as productivity between countries varies significantly. This may guide researchers, in vitro fertilization professionals, and prospective authors during literature search, while proving useful regarding manuscript design and concurring on keywords and abstract content.


Background
Following the advent of assisted reproduction, clinical embryology has become an evolving eld of interest in science. Nowadays, an enormous volume of scienti c knowledge is freely available on clinical embryology. This re ects the novel approaches and ground-breaking research performed on the preimplantation embryo, towards an e cient and safe clinical practice in the era of precision medicine.
However, the overwhelming number of published articles calls for an effective tool for managing the quantity and assessing the quality of the published academic research. The driver behind exploring the respective bibliographic databases could be fueled by various reasons and present with different levels of "search" for the practitioner of assisted reproduction. A terminal search could aim to fully capture a topic of research and advance knowledge on a speci c eld, as well as initiate or resume a debate regarding a current trend such as day-3 versus day-5 embryo transfer or optimal embryo biopsy timing for Preimplantation Genetic Diagnosis (PGD). It may focus on simply improving understanding of a subject or constitute the primary research work towards drafting a manuscript for publication. In any case, an effective search is essential and concurrently challenging to perform. The application of complimentary tools could potentially assist towards limiting, selecting and deciding upon the degree of impact characterizing an article.
Perhaps the effort to depict academic distinction in a digestible way is challenging by nature as it is a multi-dimensional issue that fails to be properly addressed by simply applying mathematics and statistics. This fact renders this work timely and essential, uniquely bringing to the literature a rst attempt to describing the entity of clinical embryology research the body of clinical embryology in its entirety to date. This study aims to objectively and resourcefully portray the status of research in the eld of clinical embryology by employing unbiased bibliometrics tools. The authors present the application of these tools in order to determine and de ne the currency all researchers should "pay" to establish their publication value in the competitive and fascinating world of science. Speci cally, in the present study the authors i) individually assess: "In vitro Fertilization", "Intracytoplasmic Sperm Injection", "cleavage stage embryo", "blastocyst", "embryo culture conditions", "Preimplantation Genetic Diagnosis/Screening/Test" and "embryo cryopreservation". ii) present the most bibliometrically highlighted scienti c contributions with regards to the milestones of clinical embryology, iii) evaluate the difference in the number of publications longitudinally and geographically) present the top 30 contributing authors, for each distinctive area of research v) visualize the yearly published articles, clusters and collaborations of authors, along with the geographic origin of publications. Further to that, this article aims to assist the researcher and practitioner of assisted reproduction on how to better navigate the overwhelming volume of data published in the eld of clinical embryology.
Bibliometrics consists of several mathematical and statistical tools applied to evaluate scholarly publications (1). Theoretically, an in uential published article will probably manage to affect other researchers' future work, rendering that article's value high. Certain indexes evaluate the in uence an article exerts based on different criteria, although often the number of citations regarding a study is preferred (2). Despite the variety of bibliometric tools that could be employed, none of them claims to be signi cantly superior to another, yet they remain a complimentary means if properly implemented during research.
Reporting on the number of articles published by an individual scientist is a simple way to perform a quantitative evaluation, yet not indicative of the value or quality of their work (3). Besides the evaluation of authors, journals are ranked in order to indicate their productivity (2). There are numerous author-level metrics including: total number of publications, total number of citations for all publications, average number of citations, author impact factor (IF) (summary of the IF of the journal that the author has produced publications in), h-index and g-index. H-index is a citation metric that mirrors the quantity and the quality of a speci c author's publications (4). H represents the largest number of an author's publications that have been cited at least H times (5). H-and g-indexes are similar, with the former being a preferred and more commonly employed option of the former, though g-index is newer and mathematically more complex. Nonetheless, h-index is still being considered as a controversial authorlevel metric index. Another commonly employed index is the m-quotient (h-index/years) presenting the quality and quantity of the author's publications in accordance to their publication years. Finally, the hreal is the h-index of each author excluding self-citations. In terms of journal-level metrics, IF provided by Web of Science (WoS) is the most accredited index. There are two other major indexes, called the Scimago Journal Ranking (SJR) and h5 index by Google Scholar.
The eld of "Reproductive Biology" according to WoS is named "Reproductive Medicine" in Scimago and "Reproductive Health" in Google Scholar.

Search Strategy
The WoS and Scopus database were thoroughly searched. Opting for these databases was a prerequisite since bibliometric tools are not available in other databases. The WoS was excluded due to returning duplicate publications and authors. Therefore, the Scopus database was used exclusively in order to limit the overlap in results for individual author searches. For example, a certain author may be searched and subsequently found in the results of the search with a different identity multiple times, depending on whether the search employed initials, the author's rst name, or surname. Moreover, when compared to WoS, the Scopus database offers 20% more coverage among citations in biomedical publications (6). The search was performed in October 2018. Identi ed articles corresponded to publications from 1978the year of the rst publication on assisted reproduction-till 2018.Regarding journal data, the WoS database was used as it presents the most accredited IF (by Clarivate Analytics). The other indexes on journal data were extracted from Scimago and Google Scholar.
The keywords employed were "In vitro Fertilization", "Intracytoplasmic Sperm Injection", "cleavage stage embryo", "blastocyst", "embryo culture conditions", "Preimplantation Genetic Diagnosis/Screening/Test" and "embryo cryopreservation". These keywords were selected with the aim of fully representing not only the current and trending research areas in clinical embryology, and re ecting the scienti c interest in the eld throughout decades of progress in clinical embryology. The selection was performed aiming towards an all-inclusive approach in presenting the eld of clinical embryology. The rationale behind keywords' selection was based on the observation that employing solely generalized search terms such as "In Vitro Fertilization" would result in failing to include a wide range of studies, among which some representing pivotal contributions in the eld. On the other hand, excluding general keywords such as "In vitro Fertilization" would fail to yield some of the seminal older studies in the eld.
One limitation of this study was the inclusion of certain articles focusing on "animal models", "developmental biology", and "embryonic stem cells", due to their relevance and high a nity to clinical embryology. However, they do not exclusively refer to practice of clinical embryology within the Assisted Reproductive Technology (ART). The keyword "animal models" could not be excluded as various studies referred to them and included the speci c phrase within the abstract. One striking example is the study by Edwards and Steptoe in 1978, which established the eld of clinical embryology (7). The keyword "developmental" could also not be excluded since numerous studies refer to the developmental potential of the preimplantation embryo. The keyword "stem cells" was fully excluded from our study. Nonetheless, aiming to exclude articles from stem cell research could not account for articles on the same eld describing them as pluripotent or totipotent. In order to overcome these identi ed limitations and exclude studies unrelated to clinical embryology, the subject area was limited to include only "Medicine", the elds of "Veterinary", "Agricultural and Biological Science", "Neuroscience", "Environmental Science", "Engineering" and "Chemical Engineering". This search is fully reproducible and the exact search string is available in supplementary material A.
A similar search was performed on PubMed employing the "RISmed" package and analysis was performed employing the "bibliometrix" (8) package in R programming language. The aforementioned keywords were employed as MeSH terms. Since the "bibliometrix" package disregarded articles, it resulted in index score discrepancies. Therefore, author-level metrics obtained through this search were excluded, as they did not correspond to metrics provided by other databases. The authors with the highest number of publications were searched in Google Scholar database, employing "Publish or Perish" (6th edition) software (Harzing, A.W. (2007) Publish or Perish, available from https://harzing.com/resources/publish-or-perish). The network maps employed to present results of this analysis were created using the VOS viewer software (build 1.6.9). Retracted papers where obtained by retracted-watch database.

Statistical analysis
The statistical analysis was performed in R programming language. Differences in number of publications were evaluated using the chi square test; similarity was assessed employing Jaccard's Index while rankings were evaluated employing Spearman's Correlation coe cient. Con dence level was set at 95%.

Results
It should be highlighted that the eld of clinical embryology is notably expanding, recently reaching almost 2,100 publications per year, indicating an explosion of interest within the scienti c community.
The trend in publications presenting cumulative numbers of published scholarly articles evaluated yearly is presented in Figure 1.

Authors and their contribution
In the Scopus database, employing the keyword "In Vitro Fertilization" yielded 41,292 results. The author with the highest output was identi ed as Devroey P., having co-authored 384 publications. The keyword "ICSI" or Intracytoplasmic Sperm Injection" returned 8,464 results. The author with the highest output was Devroey P., having co-authored 167 publications with the common denominator between them being the aforementioned keyword. The search string of the keyword "cleavage stage embryo" returned 2,510 results, while the author with the highest output was identi ed to be Handyside A. H., with 27 publications in this area. The keyword "blastocyst" returned 9,492 results. D.K. Gardner was the author with the highest output in the eld with 83 publications. The same author also presented the highest output regarding "embryo culture conditions", having co-authored 14 out of 1,981 publications in the speci c eld. In the eld of "Preimplantation Genetic Diagnosis/Screening/Test" a total of 3,778 publications are listed in the database, with Munné S. with the highest output of 123 publications. Finally, the search in the eld of "embryo cryopreservation" returned 5,770 results. The author presented the highest output was Devroey P., participating in 76 publications. The top 20 authors in each eld are presented in Supplementary Table   I.
The publications of the top 5 authors in each research eld were analysed and compared to the total number of publications in the respective eld. The research eld regarding Preimplantation Genetic Diagnosis/Screening/Test (PGD/PGT-A) contained highest percentage of publications produced by the top 5 authors (11%), followed by the search terms "ICSI" (7.3%), "embryo cryopreservation" (5%) and "cleavage stage embryo" (4.4%). The search terms "In Vitro Fertilization" and "blastocyst" presented with rates of 3.6% and 3.5% respectively. The search term with the lowest rate of publications conducted by the top 5 authors was embryo culture conditions with a rate of 2.4%.
When combining all of the above searches and keywords, a total of 54,522 results were generated. The author with the highest output was Devroey P. with 482. The search in PubMed yielded 64,075 results.
The author with the highest output was Devroy P., similar to employing the Scopus search engine, albeit with a lower number of publications (447). A serious limitation of the search in PubMed was the number of articles for which the authors were not available (573). For the number of articles that correspond to "Reproductive Biology" the difference between PubMed and Scopus was statistically signi cant (p<0.001).
The h-index was evaluated for the top 30 authors in the clinical embryology eld using Scopus. The hindex of the top 5 authors for each sub-eld of the eld was also evaluated. The h-index reported for the top 5 authors ranged from 100 for Devroey P. to 22 for Borges. The h-index of top authors for each subeld is presented in Table 1 along with the number of publications and the number of documents that have cited each author. The h-index and the number of publications in the eld for the top 30 authors are presented in Figure 2, while the number of publications for the top 5 authors in each sub-eld is presented in Figure 3. The h-index, g-index and m-quotient as obtained by both Google Scholar and Scopus are presented in Table 2 for the top 10 contributors. H-index -as provided by Scopus and Google Scholar-did not present any statistically signi cant difference. Figure 4 presents an attempt to chromatically visualize the clusters and collaborations of authors, while the magnitude of number of citations is highlighted and indicated by font size.
In an effort to present the up-and-coming authors, an analysis of the publications and of the h-index of the top authors was performed for the ve year period from 2013-2018. The top 30 authors according to the h-index assessed based on the publications since 2013, are presented in Table 2. With the exception of 5 authors that are present in both Tables 1 and 2, the remaining authors presented in Table 2 are in fact researchers that are emerging to be recognizably proli c in the eld of clinical embryology. To evaluate the overlap between the two Tables, Jaccard's Index was used and was estimated at 0.098, meaning that the two tables share data and authors to an extent of 9.8%.

Analysis per country and institution
The United States of America (USA) produced the highest number of publications (12,537), with more than double those from the United Kingdom (UK) (5,225) according to Scopus. The USA remained the country with the highest contribution when PubMed results were analyzed, with the second place being occupied by China, while the UK occupied the 13 th place. Interestingly, according to Scopus, the most frequently encountered a liation as reported by the authors was "Inserm", the National Institute of France. The search in PubMed resulted in the Tel-Aviv University being the most frequent reported a liation by authors. Nonetheless, the second most frequent reported a liation was not available, rendering the results of whole search as of low quality. Exact data for the top 20 countries and institutes are presented in Table 3. A world map depicting the publications by country -according to Scopus-is presented in Figure 5 and the ratio of single and multi-country publications -according to PubMed-is presented in Figure 6.

Journals
Regarding journal bibliometrics, based on the year 2017 metrics, there are only 29 journals according to WoS that refer to "Reproductive Biology", ranking it 187 th among 235 disciplines. Out of 29 journals, only 4 are not dedicated to human studies. According to Scimago, there are 70 journals relating to "Reproductive Medicine", and according to Google Scholar there are 20. The difference in number of journals in each list is statistically signi cant (p<0.001). When ranked by the number of total citations number, "Reproductive Biology" ranks higher at 135 th with more than 204,000 citations. Regarding the journal IF, the eld of Reproductive Biology ranks 83 rd on aggregate IF and 30 th on the median IF category corresponding to the top 13 th percentile. Only 7 retracted articles were identi ed in the eld of Reproductive Biology among the 54,522 articles (0.0128%). The comparison regarding the ranking of journals between the lists was evaluated using Spearman's Correlation Coe cient. In all 3 possible combinations the ranking was positively correlated, albeit not absolutely. Journal rankings according to each index are presented in Table 4.

Highly cited articles
When comparing on an article basis according to Scopus database, only 4 articles exceed 1000 citations and only one exceeds 2000 citations. The top-cited article in the eld of clinical embryology is the "Pregnancies after intracytoplasmic injection of single spermatozoon into an oocyte", the study that established the procedure of ICSI. Interestingly the study that established the eld, "Birth after the reimplantation of a human embryo", is in second place. When comparing the mean citations per year "Pregnancies after intracytoplasmic injection of single spermatozoon into an oocyte" reaches again the top of the list with an average of 94.35 citations, followed by the 2005 "ESHRE guideline for the diagnosis and treatment of endometriosis" with an average of 72.54. The top-10 most cited articles are presented in Table 5.

Discussion
In the current study, we present an overall quantitative and qualitative assessment of authors' performance in the eld of clinical embryology, speci cally regarding research on "In Vitro Fertilization", "Intracytoplasmic Sperm Injection", "cleavage stage embryo", "blastocyst", "embryo culture conditions", "Preimplantation Genetic Diagnosis/Screening/Test", as well as "embryo cryopreservation". The respective areas of clinical embryology have been researched and investigated separately. The h-index was used to contribute towards objectively re ect the scienti c value of publications, their weight and their identity within the volumes of studies available. Our results indicate that each eld includes a diversity of unique authors who excel in their "arena of interest". It should be further highlighted that the keyword yielding the highest number of publications was "blastocyst" followed by "ICSI". This conclusion comes as no surprise since both "blastocyst" and "ICSI" have been in the spotlight of debate in the eld of clinical embryology during the past decades describing the optimization of ART. The data regarding the top listed authors presented here may be viewed as portraying the foundation of research, as well as novel approaches in our eld. The high percentage of publications produced by the top-5 authors (11%) was attributed to the research eld of PGD/PGT-A re ecting the particular specialization of the eld. Bibliometric tools succeeded in portraying and identifying authors that were expected to be yielded for each of the research areas investigated. Interestingly the h-index attributed to the top listed authors' ranks considerably high when compared to the list of the top h-index in the overall medical eld, re ecting the value and prestige of the eld of clinical embryology in medicine.
It should be noted that different databases yield different results. The search in Scopus and PubΜed resulted in a statistically signi cant difference in the number of articles. PubΜed fails as a means for bibliometric evaluation, as the only tool developed so far enabling bibliometric analysis in PubΜed provides a limited number of results. A possible reason behind this is the fact that PubΜed was not designed for bibliometric research, thus it requires huge computing power and numerous burdens in acquiring all the necessary data. It may be possible that modi cations in the packages employed for mining citations from the PubMed database may enable available for bibliometric analysis in the future. It is worth mentioning that the "bibliometrix" package that was employed in this study, has only been available since last year, thus future upgrades may present as a solution to the aforementioned problems.
The journals on the eld of Reproductive Biology are limited when compared to other disciplines. The high number of citations in the eld, as well as the high ranking on journal IF metrics re ect the high quality of journals in the eld. When evaluating from the perspective of the journals serving as the platform of communication of research, it is important to consider that the limited number of journals publishing on the eld of clinical embryology correspond to a median IF that ranks high and reaches the top 13th percentile as stated in our results. This fact is supported by the small number of retractions of articles within this eld proving that the review process in place is of e cient. The average retraction rate of 0.025% (9) is double compared to the one reported for the reproductive biology eld. It should be mentioned that various different journal-level metrics exist. The most recognizable of these are IF by WoS, SJR by Scimago and h5-index by Google Scholar. The three different indexes provide alternative scoring systems regarding journal metrics. Although the parameters assessed for scoring are different, the ranking is positively correlated between all indexes indicating a high level of agreement.
Highlighting the authors and respective research groups performing advanced research in several elds of clinical embryology was a principal aim of our investigation, as well as assessing their respective contribution amongst highly valued publications. However, it should be noted that these authors primarily present data sourced from team effort and therefore the respective articles do not correspond strictly to an individual researcher's contribution. Each author's contribution within a manuscript may vary, since different tasks may be executed by different authors in most published articles. Notably, the most frequent number of authors in each paper is 6, though there has been a decline in the number of articles listing 7 or more authors. A visual representation of the number of authors per publication is presented in Fig. 7. Although examining publications under the prism of team performance may be more appropriate, it is extremely challenging to approach effectively. This is attributed to the fact that research groups tend to vary and are subject to change, with the exception of the senior author also known as "last author" serving as the leader, or senior supervisor of the research group. Nonetheless, the concept of team contribution was qualitatively represented in this study as the network map seen in Fig. 4, which shows the co-authors that tend to publish collaboratively. Approaching research productivity according to geographical classi cations is of interest. As seen in Figs. 5 and 6 the majority of publications originate from North America followed by East Asia and European countries, as expected with regards to investment in research. It has been documented that international collaborations are found to be more common in top productive countries. As productivity between countries varies signi cantly analyzing collaborations may be of bene t, serving as a driver to promote research. The degree and nature of collaborations along with the topics would dictate advancement of the eld. With respect to the analysis of the top-authors corresponding to the last ve years, it becomes apparent that there is a considerable in ux of new researchers contributing signi cantly to the eld, a fact con rming the ever evolving nature of clinical embryology. The Jaccard's index set at 0.098 leads to the quanti able conclusion that the majority of research publications from the past ve years were contributed by "new" authors. The term "new" refers to researchers in clinical embryology that were not identi ed as top-authors with regards to the past 40 years as presented in Table 1. In fact, considering that the overlap between Tables 1 and 2 refers to 5 authors, it is of interest that this aforementioned majority of new contributors represents the 85.3% of the top authors of the last ve years.
Bibliometrics present not only as a useful tool in the hands of the person conducting a research, but also for the scientist acting as an author. Evaluating the impact of a published article is a requisite for all authors who wish to assess the re ection of their work in the scienti c community (2). However, unprincipled prerequisites should be considered such as the precondition of citing speci c journals in an article before an author is allowed to publish there (10). Moreover, the concept of negative citations is interesting, as instances are recorded when articles are not cited on the grounds of supporting or disagreeing with the respective conclusions, but rather to dispute the statements presented therein (11). Perhaps accounting for negative citations could be addressed in future analyses.
As anticipated, the papers that introduced and established the eld and some of the sub-elds of clinical embryology ranked at the top of the list regarding the number of citations. Most top-cited studies were published in the 00's (4 studies), followed by the 90's (3 studies), the 80's (2 studies) and the 70's (1 study). Among the top-10, three papers served to introduce and establish the respective elds, 2 papers present guidelines and two others are systematic reviews and/or meta-analyses. This is the rst study to present an assessment of publications in the eld of clinical embryology along with speci c sub-elds. This article attempts to raise authors' awareness regarding several essential issues arising from this study. The selection of keywords, the suitability of the title and an accurate abstract section are matters that merit further attention prior to publishing an article. While conducting our investigation, there was no overlap as one would expect to encounter, between results yielded from the keywords used. The keywords "In Vitro Fertilization" and "Assisted Reproduction" yielded articles that did not overlap as expected, rendering the selection of appropriate keywords for our investigation a challenging task. Thus, when considering keywords prior to publication, it is important to ensure that one's appropriately portrays the research involved as well as effectively communicates to a targeted audience. The authors have presented a network map and clustering on keywords as they were detected in abstracts. As shown in Fig. 8 the word "fertilization" appears to be common among all possible searches, whereas "blastocyst" and "preimplantation diagnosis" appear to be more secluded. Nonetheless, it is clear that synonyms or interchangeable terms may vary in increasing or diminishing an article's index value. Figure 9 shows the number of articles employing these keywords throughout the years, portraying the extent to which they re ect the strength of the various research sub-elds. Throughout the years the term "In Vitro Fertilization" appears to be the most commonly used in studies regarding reproductive biology and clinical embryology. It should be emphasized that the topics of "PGD/PGT-A" and "ICSI" were more recently introduced to the eld when compared to "In Vitro Fertilization" or "culture media".
This study attempted to familiarize scientists within the eld of clinical embryology with bibliometric markers. The process of researching published articles of interest may focus on researching names of praiseworthy authors and testing key-words, despite at times both failing to accomplish the desired end-point. The data presented may assist researchers in navigating the overwhelming volume of publications, towards ltering and evaluating published articles in the era of precision medicine. It is common knowledge to experienced embryologists and practitioners that clinical embryology is evolving fast. Nonetheless, that may not apply to younger colleagues in the eld who may nd such information interesting and valuable. The holy grail of researching remains to be a less perplexing and time consuming, albeit more effective "search". It appears that bibliometrics may present such a promise. Nonetheless, it should be noted that a tool employed to improve the system could result in more troubling consequences, such as de ning an "elite" among research groups and respective rst and senior authors. Furthermore, acquiring a list of prestigious authors may result in predisposed reviewers (4) and "intolerant" journals towards what may be described as "weaker" authors.
The authors refrain from suggesting means or a strategy to improve use of bibliometric tools, as they stand independently and that is the strength conveyed by mathematical concepts and approaches which represent the core of bibliometrics. It is our view that bibliometric tools should be employed within the scope of conducting research, familiarizing and comprehending a certain topic in depth by identifying prized authors. In the era of abundance of information, research engines and overwhelming amounts of data, bibliometrics should be employed in making the decision to prioritize. However, the perils involved at solely relying on bibliometric tools should be highlighted. One could ponder, "how could an important scienti c contribution by a new search group counterbalance its bibliometric weakness and successfully reach its target audience?" New research groups embarking on investigations may be underrepresented and hence fail to reach the wider audience with the same ease, a fact that should be accounted for. Whether bibliometrics are a valuable tool for evaluating performance is still unclear. Until a more complex formula is introduced-as suggested by Hicks (12)-reading and individually evaluating a published work is the most appropriate and robust way to assess an individual's expertise. Mathematics and their objective nature may not always be the answer. The intuition and personal judgment of each respective reader are fundamental components of the process of evaluation.
The focus of this work was not to discuss the performance of top-listed authors. This is clearly presented in the results section and no further analysis is required. Their contribution to clinical embryology has been unanimously recognized on various levels, since it has undoubtably progressed the eld and conveyed excellence in fueling safe and effective practice. The focal point of this research was to demonstrate the value of bibliometric tools as used here. It appears that the use of tools such as h-index, number of publications and number of citations could offer insight into the importance of scienti c contributions in the eld of clinical embryology. It may further assist in identifying the "stronger" contributions with respect to reaching a larger audience and making an impact in future studies as evidenced by citation analysis. However, the fact that time -sometimes extensive-is required for a published paper to be fully bibliometrically evaluated should be highlighted. Evaluating the impact that a scienti c team's work exerts through the citations corresponding to a publication may entail confounders. Recent publications may remain bibliometrically "concealed" with respect to citations subsequently pro ling the h-index for the respective authors. The period during which a paper does not appear to be bibliometrically recognized is de ned by the period that is required for drafting, submitting, revising and publishing subsequent articles that will include them in their reference list.
This article provides an all-inclusive analysis employing bibliometric tools to assess the level of clinical embryology research. The authors discuss top-ranked contributions, countries, and journals while considerations and special considerations raised are indicated. When called to assess the overall performance of the eld employing bibliometric tools it should be highlighted that clinical embryology was introduced in literature in 1978 and it is therefore considered a rather "young" research eld in Medicine. This fact may set the tone accordingly. Notably, a steady increase in scienti c interest and production has been observed in the eld of clinical embryology since its conception marking the continuous improvements documented in clinical practice.

Declarations
Ethics approval and consent to participate Due to the nature of the study and dataset, it was not necessary to obtain informed consent or approval from an institutional ethics committee.