What Happens with the retrieved eggs in the Laboratory?  

Once the eggs are retrieved, they are incubated with sperm in specialized culture media. Typically, the partner’s sperm is collected shortly before or a few hours prior to egg retrieval.  

1. Semen Processing  

• The semen sample is liquefied at room temperature.  

• It is then prepared to remove seminal fluid and select the most motile sperm.  

2. Fertilization  

1 to 4 hours after egg retrieval, the eggs—still surrounded by their follicular cells—are placed in culture with 100,000 to 150,000 motile sperm per milliliter.  

3. Fertilization Check  

• After 18 to 20 hours, embryologists examine the eggs to confirm fertilization.  

• Successful fertilization is identified by the presence of two pronuclei (one from the egg, one from the sperm) inside the fertilized egg, which is now called a zygote.