I am very sorry to hear about this. If you think you have a possible medical malpractice/wrongful death suit against a doctor or other health care provider, it would be best to go ahead and request your medical records related to this and start contacting local attorneys who handle medical malpractice and wrongful death suits. You are likely limited to a two year statute of limitations from the date of the negligence/malpractice. Thus, suit would likely need to be filed two years from the date of negligence/malpractice. A local attorney familiar with your state laws can further assist you. These case are very difficult to litigate and usually require the hiring of an expert witness prior to a suit even being filed. That is why I recommend that you seek the assistance of an attorney. The expert will need to be another doctor who will testify and offer evidence/proof that the doctor who was treating you and your unborn child committed negligence/malpractice which was below the standard of care and resulted in the injury/wrongful death of your unborn child. A lawyer will likely want to review the medical records related to this so I would go ahead and request the records from the hospital visit where/when the malpractice occurred. Best of luck!
NOTE: This response is general in nature and should not be considered legal advice. No attorney-client relationship exists or is formed by this response.