Brief Answer:
You need an ultrasound scan.

Detailed Answer:
Hello,
Thanks for trusting us with your health concern.
At three and a half months, if the bag of water has ruptured and all the water around the baby has drained then the chances of survival of baby till term are very less. You can get an ultrasound scan done after consulting your gynecologist to find out the fetal well being and the abnormality.
Please feel free to discuss further. I will be glad to answer the follow up queries that you have.
Wishing you good health.
Regards.
Dr. Rakhi Tayal.
For future query, you can directly approach me through my profile URL http://bit.ly/Dr-Rakhi-Tayal

---