I'm a little unfamiliar with the precise step-by-step process but if the placenta doesn't form it's not like there's no fertilization it just creates a guaranteed miscarriage. Though it would probably happen before anyone would know they're pregenet.

I'm a little unfamiliar with the precise step-by-step process but if the placenta doesn't form it's not like there's no fertilization it just creates a guaranteed miscarriage. How far along to where placenta becomes really relevant would determine if we see an epidemic of miscarriages.