Pronuclear Stage
Pronunciation: pro-NEW-klee-ar
The developmental stage approximately 18 hours post-fertilization when male and female pronuclei are visible before fusion.
Full Definition
The pronuclear stage represents a critical checkpoint in early embryo development, occurring roughly 16-20 hours after fertilization. During this stage, both the male and female pronuclei are clearly visible within the cytoplasm of the zygote but have not yet fused. Embryologists assess pronuclear morphology and positioning as indicators of embryo quality and developmental potential. Normal fertilization is confirmed by the presence of two pronuclei and two polar bodies. This stage precedes the first mitotic division and is used for timing subsequent culture and assessment protocols.
Usage
Usage note: Often abbreviated as 2PN stage in clinical documentation; hyphenate when used as adjective.
In Context
- "Embryo assessment at the pronuclear stage revealed normal fertilization with two distinct pronuclei." — Laboratory report
- "The pronuclear stage evaluation is critical for determining which embryos to culture to blastocyst." — Clinical protocol