3lbs at 30 weeks isn't extremely small. lol. Small maybe but not "extremely" small. They also can be off on either the pound or ounces. Its not 100%. At 32 weeks baby was measuring 4lbs and my doctor said that's right on track. My first son was born at 37 weeks at almost 7 lbs and my second son was born at 37 weeks at almost 8lbs and they were both guessed to be 3.5 lbs around 30 weeks.