Board Thread:Warhammer 40k General Discussion/@comment-7699236-20150618150629/@comment-28917471-20151213132719

Let's not forget that the gene-seed came from the Primarchs  (who were all males). Meaning that the gene-seed will work only in male body. The women won't be able to survive the implantation no matter how trained or strong-willed she is.

There are even circumstances where well trained men did not survive the implantation.