Most places that cater to pregnant women have a pretty strict no sickness policy since it can be harmful to unborn babies. What gives one person the sniffles can give another a raging fever (very dangerous for a pregnant person). You risk them turning you away and making you reschedule if your son is pretty obviously sick. At least that's how I'd tell my husband no. They rarely last more then an hour, Maybe a neighbor, friend or relative could stop over for a little bit.

I wouldn't want to take my son out when he is sick either to risk him being sick longer tell your husband you will record the ultrasound on your phone for him and of course bring pictures ... Good luck I hope he understands!