If, like some pregnant women, you are feeling big for this halfway stage, it doesn't necessarily mean that you'll have a big baby. Being large doesn't mean that all your weight is in your belly and from your baby; you may have put on weight on the rest of your body that doesn't affect your baby's size. Women who are carrying twins or triplets do, of course, show earlier and have much larger bellies than those expecting one baby.
The size of your belly is, however, a good indicator of your baby's growth, so it will be measured by your doctor (see Measuring your baby). She will measure from a point on your pubic bone in your pelvis to the top, or fundus, of the uterus. This measurement should correlate with the number of weeks you're pregnant, with an accuracy of within 3/4 in (2 cm). So, if you're 28 weeks pregnant your belly should measure 10 1/4-11 3/4 in (26-30 cm). This symphysis fundal height (SFH) will be written in your notes.
If your belly is found to be significantly larger or smaller than it should be for your dates, you're likely to be referred for an ultrasound scan since this can give a much more accurate measurement of your baby's size.
Remember, though, what you think of as huge and what your doctor feels is too large can be two very different things! You are used to your body being a certain size and shape and you are much bigger than you used to be, even though to doctors you are a normal and healthy size. This can feel particularly the case if you're someone who has always been slim.