ILR Wife- Maximum Absences from UK in the two year period

Hi,
What is the maximum number of days a spouse can be out of UK in the two year period to be eligible to apply for ILR. She will aplly for ILR as the spouse of a person presently settled in UK?
My wife is pregnant and she intends to give birth in India. She will be way for at least 3-4 months.
Will it have an effect when she applies for ILR at the end of two year qualifying period?
Are there any restrction on the number of days she can be out of UK
a. in the two year period.
b. in a single stretch.

Thanks.