McDonald rule in pregnancy

The Mcdonalds rule in pregnancy is a rough determination of fetal age in weeks compared to uterine/fundal size. It is done by using a measuring tape to measure from the top of the pubic bone to the top of the uterus, where the uppermost part of the protruding belly "meets" the top of the abdomen. It is like you are measuring a "hill" from base to base. The measurements in centimeters usually equals the weeks of gestation, plus or minus 1-3 weeks. for example, if the fundus measures 26 centimeters, then the fetus is about 26 weeks old (23-29 weeks). This is difficult to achieve accurately in obese patients. It is not done quite as much in doctor's offices anymore, because ultrasounds are a little more accurate. It is still a good determination of fetal development that is cheap and easy to perform.