Almost 30 weeks and baby is almost 4 lbs!!

I had my last monthly dr apt yesterday and from here on out I will go for my bi-weekly apts. I asked the dr what my total weight gain was and she said 17 lbs so far. I felt like that wasn't so bad, except she said she's estimating the baby at almost 4 lbs already! I knew my belly was getting big, but now I'm worried she will be too big for natural birth! The dr suggested a low carb diet and that will help the baby not get too large. :( I'm going to do it for my baby but I never expected to have to diet while pregnant 😩