Ambien is an FDA approved drug for use as a sleeping aid in the United States. With such approval, the company manufacturing the drug is required to undergo a substantial research process, whereby studies are conducted in to such topics as Ambien and it's relative effects on pregnancy.
Given the wide audience and difference in population that receives Ambien prescriptions, one might expect that a study in to Ambien and pregnancy would be rather complex. It would need to take in to account everything from the fetus and it's development - right through to the interaction that Ambien might have with other substances a female is required to ingest during the stages of pregnancy - such as Folic Acid, and so on.
Over the last several years, hundreds of such studies have been done, and thousands of people have reported back to the drug agencies with their own personal experiences of taking Ambien during their pregnancy. So what are the overall results?
Whilst sleeping can certainly be a difficult thing to get during the different stages of pregnancy, mothers-to-be can be reassured by the current data on hand that indeed Ambien is not detrimental to the development of a baby during pregnancy.
In fact, there has been no research to suggest that there are any negative effects for either the baby, or the mother, if she continues to take the drug during pregnancy.
Obviously, however - it is up to you to decide whether or not you think that taking Ambien during pregnancy is a good idea or not. Perhaps you have reason to believe that it is something which could be detrimental to the child, or perhaps you would just like to err on the side of caution.
If this is the case, and the doctor is recommending that you start on Ambien to treat a sleeping disorder - the best recommendation would be to discuss your concerns with you doctor - whilst you are there at the office. It may be the case that someone else can be prescribed (ie. a herbal alternative, etc) which can do the trick in your circumstances.
However, you can certainly rest assured that from a medical standpoint - countless hours of research show that there really is nothing to be worried about.