The purpose of this study is to prospectively define a set of data suitable for developing models of pregnancy viability. Those models will be based on serum hCG concentration measured during the peri-implantation period in patients that received fresh embryo transfer and those that received transfer of frozen-thawed embryos, and to compare and contrast these models. This may reveal insights into differences between these types of IVF cycles.

The current study seeks to examine the effect of the timing of implantation (as indicated by the first increase in serum hCG level) on the viability of pregnancies and to determine if such effect of timing differs between fresh embryo transfers and frozen-thawed embryos transfers. In this case, the timing of implantation will be measured through serum hCG analysis on days 3, 4, 5, and 7 after blastocyst transfer.

Inclusion Criteria:

• IVF patients (adults) who received blastocyst transfer

Exclusion Criteria:

• Those patients using different laboratories

IVF patients