Former competitive woman soccer player here--stopped playing at 22. I ran marathons, lifted, trained, exercised consistently once I gave the sport up. I have always exercised 5-6 days per week every week.
I was pregnant with my first at 34 and I exercised up until the day I gave birth---10 days after my due date. I had a very easy, uncomplicated pregnancy and I heard the longer the weight stays on the more likely it is to stay. I did not have a C-section and my labor was uncomplicated--no big tears, etc. I was up and moving right away. I strapped that fat baby in a baby Bjorn and was walking up steps, running by the end of the month, lifting. By 4 months out I was doing really great. Now---I wasn't 100% of my usual athletic self. BUT--I was 5 years older than Alex and did not have professional trainers or dieticians, therapists, etc. monitoring me and I gained 48 pounds during pregnancy

. I did have all but 5 of it off by 4 months.
The biggest problem is your core. Core strength is negligent after giving birth. You really, REALLY need to work that back up. But--arms, legs, etc---you can still lift. I was running 5-6 miles up until 6-7 months and then was still doing weights and non-impact things like elliptical and swimming.
I gave birth to my 2nd at 37, also very easy pregnancy and exercised throughout--but at that age and being the 2nd it took al little longer to get back and I don't think I was ever 100% the same after. Weight-wise yes--but my running speed, and my hamstrings, etc took a hit.
My sister had C-sections for all 3 and that is a much bigger ordeal to recover from. Although she said knee surgery was worth than birth.