What @esmith says really makes sense! I know the hospital has told me not to even take baths because of bacteria.. My only objection is my dr says to have lots of sex the last few weeks because the cum with actually help soften the cervix and help make for easier labor!! But I don't have any idea if this changes with the mucus plug mommas. Definitely ask the doc. But if you'd rather play it safe I agree, sex is safe but have him not cum in you due to bacteria! FTM so not much knowledge just bits and pieces of what I've also heard:)
i have read that its better to use condoms after losing it due to keep all chances of any bacteria entering and reaching baby. but yes completely safe.