Maybe, if she meets the requirements for a qualifying relative. That means you must have lived together all year long, her gross income must be less than $4,050, and you must have provided more than half of her support (Government benefits counts against your support). 
If you're going to claim her as the dependent, she will not get a personal exemption on her return (vice versa) because the rule is one exemption per person. 
You cannot claim the unborn child on your tax return. When your child will be born, he/she qualifies as a qualifying child for each of you; either parent may claim the child as a dependent. If you can’t decide, the exemption goes to whichever of you report the higher Adjusted Gross Income on your separate tax return.

What is a personal exemption? https://ttlc.intuit.com/replies/3299967

Can I Claim a Boyfriend/Girlfriend as a Dependent on Income Taxes? https://blog.turbotax.intuit.com/tax-deductions-and-credits-2/can-i-claim-my-girlfriend-or-boyfriend...