no, they're fake, you need to sleep with someone. pregnancy spells might increase your chances, but they're more about protecting the mother/child or you need to take certain herbs associated with fertility.
mind you there's something called 'false pregnancy' where your mind tricks yourself into believing it's pregnant, your body would show all the symptoms minus actually being pregnant. also, with technology today, a woman who has never had sex can have artificial insemination done. that's about it for virgin births.