Can healing be requested for birth defects while a baby is in utero?

This can be done, and of course healing can be requested for anything for anyone at any time. But we understand your question to be addressing the situation when you may come into an awareness that something is brewing within that is causing a problem. This also would apply to situations where there are known defects detected through genetic screening, for example, or other diagnostics such as ultrasound that may see evidence of an abnormality. There is no reason to wait to initiate an outreach to divine realm and ask for help and guidance both. This would be a good thing and would serve all involved, particularly the incoming soul.