Cryopreservation of two pronuclear stage zygotes

The German embryo protection law (Embryonenschutzgesetz, ESchG) does not allow embryo selection, but only selection at the pronuclear stage. Furthermore, only as many pronuclear stage zygotes are allowed to be selected as are planned to be transferred in the same cycle. This means that after pre-selection of, for example, three pronucleated zygotes, these three must be transferred on the same or the subsequent day. A second selection process is not allowed. Non-selected pronuclear stage zygotes are allowed to be cryopreserved for a subsequent transfer.

The same situation is present in other European countries such as Swizerland and Italy. it is illegal to cryopreserve an oocyte after fusion of the pronuclei (PN). The idea of these laws was to avoid ethical problems related to cryopreservation of surplus embryos or wastage of embryos, because these have, according to these laws, the status of individual persons.

The current situation initiates much interest in developing a refined method of cryopreserving human pronuclear zygotes. The following article will discuss that issue in details.