How could vampires mate?

The common vampire type mates on the 3rd Sunday of the month, using asexual reproduction, via its stamen. The Masquarade Vampire type, on the other hand engages in a ritual known as 'czsleiming', which results in the appearance of vampire eggs, the morning after. (!?) expression of surprise and doubt for the above. From earliest times vampire males have been known to father children with their widows. The mechanics are very much the same as they are for living people. It has never been recorded or reputed (to my knowledge) that female vampires have had children however.