Board Thread:Warhammer 40k General Discussion/@comment-7699236-20150618150629/@comment-32638586-20170721223021

"The creation of the Daemonculaba began with the rounding up of human females present on Medrengard as slaves. Once corralled, they were shackled naked within iron cages and force-fed nutrients which caused their bodies to widen and bloat to grotesque proportions. Next, the  Hereteks  known as  Savage Morticians  utilised surgical and chemical techniques as well as the sorcery of Chaos  to radically alter the slaves' internal morphology and embed within their wombs the stolen Imperial Fists gene-seed." Source is this websites article on the Daemonculaba. "E mbed within their wombs the stolen Imperial Fists gene-seed." So they had gene seed. This is as close as possible you are going to get to female space marines without ignoring the lore.