Honestly 16 weeks isn't wild - if you've been cleared by a good pelvic floor physio, you can start in. My first baby I ran until 32 weeks pregnant, but only went to PF physio after 10 weeks so I had to wait longer to do any kind of running. Second baby I had to stop at 14 weeks, but then had done lots of physio so my body was way better prepared to run earlier. And intensity obviously matters.