Keep gaining weight @ 3rd trim

Currently 31 weeks, i lost weight during 1st trim, and barely gain in 2nd trim. But now in 3rd trim im starting to gain quite fast. Im still quite petite and skinny, however my bump is big. So far i have gained almost 8kg, does this mean baby is gaining weight too ? As im always worried baby might be on the smaller side nearing to edd. #FTM