Fundamental height is a measurement that can be taken during pregnancy to assess the growth of the fetus and the development of the pregnancy. It is done by measuring from the pubic bone to the top of the uterus, and is usually recorded on the expectant mother's chart. Historically, fundal height was one of the few ways to measure pregnancy progress. Today, other measurements are available and they tend to be more accurate, but they are not as fast and can be expensive.
The only tool needed to measure the height of the bottom is a tape measure. Height is usually measured in centimeters, and around 20 weeks of pregnancy, the measurement should start to correspond with the number of weeks in the pregnancy. A woman at 27 weeks, for example, should have a fundal height of 27 centimeters (approximately 10.6 inches). As the pregnancy progresses and the uterus expands, the top of the uterus will continue to rise to make room for the growing baby.
Several things can interfere with a bottom height measurement. Sometimes it is done incorrectly, causing disparities in weekly measurements. If a woman has a full bladder, the measurement may be off. Similarly, if she has thick uterine tissue, she has had a C-section or she is pregnant with twins. Not all babies follow a growth chart perfectly either, so being a little off isn't a cause for concern. Finally, in the last weeks of pregnancy, the fetus begins to descend, causing the fundal height to decrease.
However, if the fundal height is very far from the estimated age of pregnancy or does not progress, it may be a sign that there is a problem. The fetus may be overgrowing or undergrowing as a result of medical complications. Twins or multiples can also cause a fundus height bias. If a woman's pregnancy doesn't seem to be progressing as expected, a doctor may recommend additional diagnostic tests and measures to learn more about what's going on.
The McDonald's ruler, as fundal height is sometimes known, can be a valuable tool for quickly assessing the development of a pregnancy at no cost. Experienced providers can even take measurements without a tape, using your fingers as a guide to see how much the uterus has grown. To get more accurate information, ultrasound should be used to take pictures of the uterus and see how it has grown.