I too am very possesive and quite jealous, to tell you the truth. There are a number of things you're not telling us. For instance: in what months is she?
At worse, she's about to have the baby, meaning she got pregnant after knowing you for... three months? Did you plan to have this babby? Is she happy about having him/her?
I would be totally pissed to have my bf calling exes. Hell, his ex kept sending him messages and I was really mad 'cause h'd do nothing. I told him to go meet her, talk to her and then stop it. Don't get me wrong, I'm not against them keeping in touch, but that woman would sms him at least twice a week, after 2 years of silance.
So... maybe your wife (you didn't state her age) is unsecure. She wants to be sure she's not missing anything, she wants to feel attractive and sexy... that would also explain her attitude towards you, since you've put her in this position - e.g. pregnant. Pregnant women are a hand full, I think. They're hormonal, emotional, impulsive... Wait 'til she had her baby. Trust me, when you have little creature screaming for your attention, you tend to let other people off your life.
Maybe that's is. She's simply enjoying her last moments of freedom. 'Cause once the baby arrives, nothing will ever be the same

.
Be patient and don't do anything you might regret later.
It's just a theory.... In order to find out if I'm right or wrong, you should talk to her more. Communicate. This is how relationships are saved.