conditional occurrences of child elements

Is it possible in XML-Schema to define the number of occurrences of an
element on the value of an attribute of its parent element ?

For example:
I have a parent element with name Person and attribute Gender.
Gender can only have the values 'Male' or 'Female'.
No problem sofar.
Now I want to define a subelement 'Pregant' of 'Person'.
The element 'Pregnant' should have no occurrences if the value of its
parent element attribute 'Gender' is 'Male'.
The element 'Pregnant' should have 1 occurrence if the value of its
parent element attribute 'Gender' is 'Female'.

Is it possible to define something like this in XML-Schema ?

Best regards

Jozef Aerts