Fundal height, or MacDonald's rule, is a measure of the size of the uterus used to assess fetal growth and development. It is measured from the top of the pubic bone to the top of the uterus in centimeters. It should match the fetus' gestational age, within 1 to 3 cm. A measure of 22 centimeters should be seen on a 19 to 25 weeks pregnant woman.

A shorter measure can happen for one of the following reasons:

• Fetus descent into the pelvis, seen normally two to four weeks before delivery
• Error in estimated date of conception
• Fetus is healthy but physically small
• Not enough amniotic fluid, Oligohydramnios
• Fetus positioned sideways
• Breech birth
• Small for gestational age

On the other side, a longer measure can be caused by:

• Twins, or more
• Error in estimated date of conception
• Fetus is healthy but physically large
• Too much amniotic fluid, Hydramnios
• Large for gestational age

As a pregnancy approaches its end, the fundal height will become less accurate. Obstetrics