I packed a newborn outfit and a 0-3 months one just in case. My first son was big over eight pounds and still wore newborn for a few weeks...my daughter was she in pounds and was able to wear the newborn stuff for a month.....they were both long and lean though so it depends on your baby's body type.
Ultrasound can be off by up to couple pounds. I say buy one newborn outfit and pack it in the bag your taking to the hospital along with a 0-3. My middle daughter was 6 lbs 9 oz at birth but they told me she would be over 8 pounds. Then she lost over half a pound after birth. I tried to put her in a 0-3 and her feet came down to where the knees were supposed to be. I ended up having to go buy her a few preemie outfits. Id take one of each just to be safe. Just leave the tags on if your worried itll be too small, you can always return it if it is. Good luck :)
Better to go with 0-3 and up. They grow so fast. That's what I do. Just take three outfits with you to the hospital and see which one fits better.
I personally haven't bought any newborn clothes.... I'm not sure if my baby will fit into them when she is born...but luckily they were given to us just I case. I wouldn't by a bunch if newborn clothes...
I skip the newborn stuff completely and go right for 0-3 months. My kids were big though- 8 lb 12 oz and 8 lb 9 oz. I assume this baby will be about the same.
If your baby is already 7lbs. I wouldn't buy newborn clothes or anything. I did this with my second daughter and she was born 9lbs and fit in nothing newborn. Im 38 weeks on my 4th and I bought mostly 0-3 and 3-6 months