Effectiveness of short-term, high-intensive, WHO laboratory standard-based training in sperm morphology assessment: evidence from a national program in China

Dear Editor,

Since the World Health Organization (WHO) Laboratory Manual for the Examination of Human Semen and Sperm–Cervical Mucus Interaction was published in 1980, the manual has provided internationally recognized standards for semen analysis and has played a fundamental role in the evaluation of male fertility and assisted reproductive technology.1 Despite international standards, significant variability persists in routine practice owing to differences in consumables and reagents, staining protocols, analytical methods, training backgrounds, and quality control systems. A nationwide Chinese survey confirmed marked heterogeneity in terms of morphological testing and inadequate implementation of internal quality control (IQC) and external quality control (EQC), underscoring the necessity for structured professional training.2,3

The team of the Human Sperm Bank at National Institute for Family Planning (Beijing, China) has been devoted to the introduction, dissemination, and standardized training of the WHO laboratory manual in China.2,4 This training program was organized by the National Research Institute for Family Planning (NRIFP)/WHO Collaborating Center for Research in Human Reproduction (CHN-63) for the purpose of homogenizing semen analysis results and facilitating the interlaboratory mutual recognition of test results within the region. Since 2011, members of the team of the Human Sperm Bank at National Institute for Family Planning have implemented the WHO Standardized Human Semen Analysis and Processing System and Quality Control (QC) Framework nationwide. As of December 2025, 113 small-group training sessions have been completed; these courses adhere to a small-class teaching model featuring expert practical demonstrations and a blend of theory and hands-on practice for trainees. Nearly 5000 trainees from approximately 400 medical institutions across 31 provinces of China have successfully completed both theoretical and practical training and have obtained certificates of completion, and more than 300 institutions have joined the quality control network.

However, unlike highly automated and objective semen volume and sperm concentration analyses, the assessment of sperm morphology is a subjective process that relies heavily on visual interpretation.5,6 Morphological analyses are technically demanding, highly observer-dependent, and characterized by a long learning curve.7 Their mastery is significantly more challenging than the basic method of parameter analysis, making systematic training even more critical.

To clarify the specific contribution of education to the assessment of sperm morphology, we evaluated short-term, intensive morphology training as an independent research subject. By summarizing 1 year of national training data, we aimed to evaluate its effectiveness and to define the role of focused training within the broader framework of WHO-based semen analysis standardization.

The training of the sperm morphology assessment was conducted using a decentralized provincial model. Instructors traveled to provincial level training centers. A sperm morphology assessment was performed using standardized physical quality control slides centrally prepared by the NRIFP team. During the training session, trainees evaluated these slides by light microscopy and reported their findings onsite. This training program was designed as a systematic project strictly aligned with the 6^th edition of the WHO laboratory manual.8 This course integrates theoretical instruction with practical skills development and consists of 16 h of instructional content. The core components included spermatogenesis and sperm maturation; detailed structural analysis of the sperm head, midpiece, and principal piece; standard operating procedures for semen examination; semen smear preparation techniques; and sperm morphology assessment under strict criteria at 1000× magnification. Following training, participants must establish an IQC system in accordance with WHO-recommended methods. Participating laboratories must enroll annually in the national EQC program organized by the NFIRP team. Currently, trainees are not authorized to train new technicians independently.

Between January and December 2025, 340 laboratory professionals from 268 institutions across 22 provinces completed the full training program and obtained certificates. Most of the trainees were from reproductive centers (168, 49.4%), clinical laboratory departments (111, 32.6%), and andrology or urology departments (36, 10.6%). Others came from the human sperm bank or other related departments. At baseline, a significant “standardization gap” was observed: 176 (51.8%) of the samples were subjected to Diff-Quik staining, while 115 (33.8%) were subjected to Papanicolaou staining. Of the laboratories, 178 (52.4%) relied entirely on manual analyses, whereas 116 (34.1%) employed a combination of manual and computer-assisted sperm analysis (CASA) methods, and 46 (13.5%) relied entirely on CASA. Nearly 184 (54.1%) of the laboratories lacked formal IQC protocols for assessing sperm morphology.

The transition from pre- to post-training scores demonstrated a significant shift in diagnostic proficiency. The score (mean±standard deviation) of all the trainees increased from 69.7 ± 21.8 to 94.7 ± 10.7. The data revealed critical improvements in areas characterized by high degrees of subjectivity or technical difficulty: the correct identification of the physical logic behind smear thickness increased from 68.2% to 91.3%. With respect to mitochondrial sheath recognition, correct theoretical identification of the internal midpiece structure increased from 81.4% to 95.8%. Mastery of the “strict criteria” for sperm head shape, the most common cause of interobserver variation, improved from 75.1% to 92.5%. The most remarkable progress was seen in the identification of sperm midpiece abnormalities (e.g., bent neck and insertion-site defects), with accuracy increasing from 58.6% to 87.1%. The recognition of sperm principal defect also stabilized at 94.6% post-training.

This study demonstrated that short-term, high-intensity, WHO laboratory standard-based training can substantially improve the ability of clinical laboratory technicians to assess sperm morphology. Notably, the greatest performance gains were observed in midpiece abnormality recognition and the application of strict head morphology criteria, which are well-known, major sources of inconsistency in routine practice.9 Furthermore, the post-training convergence of performance across different staining methods and analytical approaches suggests that standardized training may partially offset baseline methodological heterogeneity, as previously reported in nationwide surveys of semen analyses in China.2

In addition to technical skills, the trainees showed a clearer understanding of WHO-recommended IQC principles, shifting from subjective visual comparisons to structured quality control strategies.10 Participating laboratories have not yet been integrated into established international EQC programs. Future efforts should focus on evaluating the durability of training effects, integrating digital and artificial intelligence-assisted tools into training programs, and strengthening the link between standardized training and continuous quality control systems to achieve the sustained harmonization of sperm morphology assessment.

AUTHOR CONTRIBUTIONS

WHL and LLF designed this research. LLF, FZ, and YG took in charge of the acquisition, analysis, and interpretation of data, and drafted the manuscript. XWW, SQ, JFX, and HBZ recorded and checked the data. LLF, FZ, YQG, and WHL revised the manuscript. All authors read and approved the final manuscript.

COMPETING INTERESTS

All authors declare no competing interests.