Target females (obviously) and choose 18 -35 years old.
As interests add stuff like: Baby food, kindergarden, etc.
If the country you have has a pregnant woman magazine, add their Facebook site and the magazine as Interest.
Search for a list of baby food brands and add them as interests.
I hope I could help with these 4 sentences.
Cheers
Also probably add relationship status in a relationship/married and recently used a pregnancy tracking app
Other common interests are maybe the book “What to expect when you’re expecting” ? It's very commonly read by pregnant families . Try out woman who are interested in childbirth, pregnancy clothing