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 in weeks within 1 to 3 cm, e.g., a pregnant woman’s uterus at 22 weeks should measure 19 to 25 cm.

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
• 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
• Polyhydramnios
• Large for gestational age
• Hydatidiform Mole

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

It is very important that the patient’s fundal height be measured and properly recorded by their OB/GYNE or midwife on every prenatal visit. Measuring the fundal height is an indicator of proper fetal growth and amniotic fluid development.