As many of you know an IVF procedure includes egg retrieval following hormonal stimulation, egg fertilization, culturing of the resulting embryos and return of the best embryos to the uterus of the patient (the so called “embryo transfer”). The maximum number of embryos that can be returned to the uterus of the patient is strictly defined and detailed in Ordinance №28 of the Law for Assisted Reproduction. That number is dependent on the patient’s age, the number of previous unsuccessful IVF procedures and the developmental stage the embryos (e.g. Day 3 or Day 5).
It is important to know, however, that the transfer of 2 embryos is done NOT in order to achieve a twin pregnancy but in order to increase the chance of a pregnancy, regardless of whether it is a singlet pregnancy of a twin pregnancy. The embryos with the best morphology are transferred during the fresh embryo transfer, in other word the ones that look best. However, the embryologist can never know which embryo will implant, because there is no 100 % correlation between embryo morphology and implantation potential. That is why transferring more than 1 embryo increases the chance of achieving a pregnancy but it also significantly ups the risk of a twin pregnancy.