If you are not married to each other as parents of a common child, only the mother is entitled to custody.
If you wish to have joint custody, both parents must declare this to the Youth Welfare Office or a notary and have it notarized.
You can submit the declaration of custody even if your child has not yet been born but has already been conceived. It is also possible and sensible to submit a joint declaration of custody after the birth if you do not want to marry each other and do not want to seek a court ruling on custody.
After submitting joint custody declarations, parental custody can only be changed by a decision of the family court.