It is possible you measure from your symphysis pubis (bony bit at front of pelvis) to the top of the fundus (top of bump). It is important to remember that it is just an estimate and no two people are likely to get the same result on the same bump so don't worry if you get your measurements different from your MW.
http://www.gestation.net/fetal_growth/fhm.htm has some pics on doing it!
I measured my bump, got my DH to do it (he is a doctor so in theory knows how to) and my MW did it and there was 6 cm difference between the spread of the readings!!
I actually got my MW to show me how to do it. She got a little felt tip & drew a line where the top of my pubic bone is, then another one where the top of my fundus is, used my hands to show me what I'm feeling for etc. She was really sweet & helpful about it. At my last check-up (35+3 weeks with her) we both measured me at 34cm so I was impressed that we both got the same, lol. My doctor never even bother to measure me, but I have done so today out of interest, and I'm 37+4 weeks, measuring 35cm. I guess I'll wait n see what my MW masures me at when I see her at 38+5 wks at the end of this month!
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