Human embryo implantation in vitro: a standardized framework for basic research and clinical translation

Area of Science:

• Reproductive Biology
• Developmental Biology
• Biotechnology

Background:

• Implantation failure is a significant barrier in assisted reproductive technology, leading to infertility and early pregnancy loss.
• Current understanding relies on limited historical specimens, hindering molecular and chronological analysis.
• Observing human embryo implantation in utero is impossible, and animal models have poor translatability.

Purpose of the Study:

• To review current knowledge on human embryo implantation, integrating data from historical specimens and novel extended in vitro culture systems.
• To highlight limitations of existing in vitro culture models, particularly the lack of a maternal endometrial environment.
• To propose a standardized framework for defining developmental stages and assessing human embryo viability to enhance research and clinical translatability.

Main Methods:

• Review of existing literature on human embryo implantation, including Carnegie Collection specimens and extended in vitro embryo culture systems.
• Analysis of limitations in current in vitro culture models.
• Proposal of a standardized framework based on morphological, temporal, and functional criteria.

Main Results:

• Extended in vitro embryo culture systems provide unprecedented opportunities to study human embryo implantation dynamics in real time.
• Existing in vitro systems lack a physiologically relevant maternal endometrial environment.
• A standardized framework is proposed to unify research efforts and improve comparability across studies.

Conclusions:

• Standardized benchmarks for human embryo implantation are crucial for meaningful comparison across studies.
• Development of more physiologically relevant in vitro systems is needed.
• Adoption of a standardized framework will accelerate the development of diagnostics and therapeutics for implantation failure and pregnancy pathologies.