I'm not aware of any studies, however, every medication is rated as to its safety during pregnancy and lactation.  You can look up any drug on www.epocrates.com.  Scroll down the page until you come to the Safety Monitoring section.  There you'll find how the drug is rated for use during pregnancy and lactation.

We have an excellent discussion on our forum titled "Pregnancy, Motherhood and Chronic Pain."  There chronic pain patients share their experiences with pain medications during pregnancy.  As you will see, there are women who have taken pain medications and given birth to healthy babies. They're a great group and will be happy to answer your questions.  (If you haven't been to the ChronicPainConnection forum before, you'll need to register but it's easy and only takes a few minutes.)

Before you get pregnant, it would be a good idea to see if there's an obstetrician in your area that specializes in high-risk pregnancies.  They usually have more expertise in working with chronic pain patients who require pain medication during pregnancy.

I hope you're able to get the answers you need to have a good pregnancy and healthy baby. 

Karen