This is a retrospective single center analysis which includes all the fresh, IOC (insemination of in vitro matured oocytes) and frozen embryo transfer (ET) performed between January 2000 and December 2019 at Humanitas Fertility Center after IVF-ICSI (In Vitro Fertilization - Intracytoplasmic Sperm Injection) cycles.

The primary objective is to determine the impact of the biologist performing the embryo transfer on the pregnancy probability, in terms of ongoing pregnancy rate (OPR), defined as the number of viable pregnancies that had completed at least 12 weeks of gestation on the total number of ET performed.

Secondary end point is to evaluate whether the biologists improve their performances as their experience increases, allowing the drawing of an ET learning curve in term of pregnancies for the different biologists.

The biologist's experience was assessed in terms of number of previous interventions performed prior to the day of ET. A total of 28 operators were eligible to participate in the study. Any biologists who performed less than 100 ETs was excluded from the analysis.

Inclusion criteria:

Exclusion Criteria:

Any biologist who performed less than 100 embryo transfers was excluded from the analysis.

All the fresh, IOC (insemination of in vitro matured oocytes) and frozen embryo transfer performed between January 2000 and December 2019 at Humanitas Fertility Center.

A total of 28 biologist operators were eligible to participate in the study.