What happens if I let my CR1 visa expire and how do I get back to the US?

Stay in the US, and have your baby here.

Your question requires an attorney consultation. It is not a simple question that can be answered on this type of forum. There are many factors that would need to be considered and evaluated. I strongly suggest that you contact an experienced immigration attorney for a face-to-face consultation and give him/her all of the facts surrounding your situation. He/she would then be in a better position to analyze your case and advise you of your options.

You need to consult with an immigration attorney to be sure you do not lose your status, and to be sure you don't put your baby's status at risk either. You do not need to be physically present in the US to file an I-751, but you do need to be sure to maintain lawful permanent resident status.

You should file the Form I-751 and then you can travel overseas.If you do not file it, your CR status is automatically terminated and you may find yourself in deportation proceedings where you may be ordered deported in absentia if you are already outside the country. Once you have filed your I-751 your CR status is automatically extended for one year [work and travel authorized] Depending on where you reside, I-751 may take about 6 months or more. But remember that if you are scheduled for your I-751 at your local CIS office, your failure to appear may result in the denial of your case and commencement of your deportation proceedings will almost certainly follow.

You should consult with an immigration attorney; there are several issues that needs attention.You should not let your CR1 expired.