So, I understand that the medical profession need some cost effective weights and measures to indicate the health of pregnancies. I'm not sure about anywhere else but in the UK, the fundal height is measured at each of your midwife appointments. Essentially, the number of centimetres from the top of the pubic bone to the top of the uterus is used as an indicator that the baby is growing at the expected rate. The measurement should be (give or take) be the same as the week of pregnancy you are in (i.e. 25 weeks pregnant should give a fundal height of 25 centimetres).
The only thing is, fundal height can be grossly inaccurate. If you measure too large or too small, there may be no issue with your pregnancy at all. And even more worryingly, there are circumstances where the fundal height measurement would be 'correct' for the stage of your pregnancy when actually there is a serious issue (for example, the amount of amniotic fluid could be too high, hiding the fact that there is an issue with growth). Before you start worrying; statistics vary but higher than expected levels of amniotic fluid only incur in around 1% of pregnancies (Source: babycenter.com) and incidences of this causing any kind of issue are even less.
In my case, I measured very small for dates all the way through my pregnancy (fundal height at full term was only 33cm) and I went on to deliver a very healthy (indeed, small but perfectly formed :) ) baby boy. Although I got used to the fact that I was always going to measure small, it did cause some amount of worry as we were constantly sent to the hospital to see consultants and have extra scans. Each scan we were told our boy was growing perfectly well. Don't get me wrong - I'm glad they erred on the side of caution. But the question is, is fundal height the best way to monitor the health of the baby?