Clinical and biological parameters influencing implantation: score to determine number of embryos to transfer

Choosing the number of embryos to be transferred is a major problem in assisted reproductive technologies. This study aimed to establish and validate a score predicting implantation rates in order to help in the choice of the number of embryos to be transferred, allowing the best compromise between high pregnancy rate and low multiple pregnancy risk. Clinical and biological parameters influencing implantation rates were retrospectively analysed in 739 embryo transfers and an implantation score was established. This score was then prospectively validated in 521 embryo transfers. Three parameters (age, ovarian response to FSH stimulation and embryo morphology) appeared to be predictive of the implantation rates and were included in an implantation score (3–9). The prospective study confirmed the validity of the score since implantation rates were higher when the score increased (5.9% for score 3 versus 22.4% for score 9; P < 0.05). Therefore, success rates can be predicted by the implantation score, which is of clinical value in choosing the number of embryos to be transferred in order to decrease multiple pregnancies while keeping high pregnancy rates. However, choosing the right number of embryos to be transferred needs further studies, since the percentage of multiple pregnancies remained relatively high in this prospective study (27%)