Culture media used to support development of zygotes to the blastocyst stage is based on two basic philosophies: a single step medium "let-the-embryo-choose" or a sequential medium "back-to-nature".

For single step media, there are two types of protocol can be used for the culture of human preimplantation embryos:

1. Interrupted single medium culture, in which the medium is renewed on the Day 3 of embryo culture
2. Uninterrupted single embryo culture, in which the same single medium is used throughout the 5-6 days of culture with no replenishment or replacement on Day 3.

Investigators aim to compare the blastocyst development and clinical outcome between the two types of protocols of a single medium (with or without renewal on Day 3)

Inclusion Criteria:

• female partners were under the age of 39 years
• Intracytoplasmic sperm injection (ICSI) was performed using fresh ejaculates

Exclusion Criteria:

• Day 3 embryo transfer cycles