here here :

I worked with clients where copies of passports were needed. In passports for married women, the date of birth of the first child is usually 3-6 months after marriage. They were just lucky and they married less lucky than the rest.
and...

Not very lucky. At my previous place of work in the department there was a large engineering and technical team, consisting of some guys from 24 to 37 years old. Several of them were married, and the rest lived with their ladies for more than one year, as they now say, in civil marriage. In conversations for living on the sidelines, if they were asked why they do not get married, the guys usually said - yes, it will be time, there will be a child, we will get married. Interestingly, this is exactly how it happened to them. During my work, two of them married their friends.