Ask her to consult her gyne. She wil guide as to what to be done...be careful from hereaftr and follow birth control measures, if your wife has had a period after the delivery, ask her to go in for an IUD, and also you should use condoms. The age of baby or the duration of pregnancy depends on when she has had her last periods. From the date of her last periods, we need to see how many weeks pregnancy is there, this can also be confirmed by doing an ultrasound scan.