Early Spontaneous Twinning Recorded By Time-Lapse

Area of Science:

• Embryology
• Reproductive Medicine
• Genetics

Background:

• Monozygotic twins (MZT) occur 2.5 times more frequently with assisted reproductive technology (ART) than natural conception.
• ART-related factors are suspected to influence MZT rates.
• Previous studies on time-lapse (TL) records for MZT prediction have yielded controversial results regarding morphokinetic traits.

Purpose of the Study:

• To present a detailed time-lapse (TL) record of a rare monozygotic twin (MZT) case.
• To investigate the developmental potential of an embryo cell that escaped the zona pellucida (ZP).
• To discuss the implications for understanding MZT formation and early embryonic development.

Main Methods:

• Detailed observation and recording of a complete time-lapse (TL) sequence of a monozygotic twin (MZT) event.
• Analysis of embryo development following the splitting of a two-cell stage embryo.
• Observation of a cell exiting the zona pellucida (ZP) through a created hole.

Main Results:

• A monozygotic twin (MZT) event occurred at the two-cell stage, with one cell extruding from the zona pellucida (ZP).
• The extruded cell developed normally, indicating totipotency is not inhibited by the absence of the ZP.
• The embryo remaining within the ZP compensated for the lost cell and also developed normally.

Conclusions:

• The zona pellucida (ZP) may not be a barrier to early embryonic cell development or extrusion.
• Early cell extrusion from the ZP can lead to the development of viable embryos, potentially contributing to MZT formation.
• This case provides novel insights into embryo development, zona pellucida function, and MZT etiology in ART.