[tbw2]

Pregnancy in and of itself requires an autoimmune suppression so that her body won’t reject the embryo. It would make sense if a few rogue sperm or tissue cells made it through, too, via the entry way conception creates.

[Maelstorm]

Yep.

[Izzy Dunne]

Pregnancy in and of itself requires an autoimmune suppression so that her body won’t reject the embryo.

But is that suppression the result of pregnancy, or the result of the presence of semen/sperm?

I wonder...

Maybe the never-pregnant women were using BC pills, which prevent pregnancy but not the immuno-suppressive action of the semen?

You'd have to test a virgin group to find that out.