I truly believe that they can! We had just gotten Bouncer (Chinese Shar Pei now at the Bridge) and 2 weeks later, I was pregnant with my DS (almost 13 years ago). Bouncer was a mean puller, very strong. He was 8 or 9 months old at the time and came to live with DH and I after BIL decided he no longer wanted Bouncer (whole other rant!!). He was also a huge jumper...hence his name, Bouncer. Well, after Bouncer came to live with us permanently, I found out I was pregnant 2 weeks later. After that, Bouncer never pulled and actually would step out in front of me if someone was walking towards me when I walked him. He also stopped jumping on me...he'd actually pop up in front of me, then bounce off towards the side...never actually landing on me. He was also very protective of me during this time.
Now, prior to being pregnant, he would pull like crazy, jump all over, etc...
Then, as soon as DS was born 9 months later, he was back to his old tricks (so long as I wasn't carrying the baby)!!!! He went right back to pulling and jumping all over me. I should also mention that when he stopped doing all that to me while pregnant, he continued his bad habits with everyone else. We were first time dog owners and didn't know any better about how to control the jumping and stuff at first. Later we took BOuncer to training classes and he got better but if he was excited...watch out!