Fundal height

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Fundal height, or McDonald's rule, is a measure of the size of the uterus used to assess fetal growth and development during pregnancy. It is measured from the top of the mother's uterus to the top of the mother's pubic bone in centimeters.

Illustration of fundal height at various points during pregnancy

Diagram showing the gestational age (on the x-axis), as related to the fundal height (on the y-axis), with blue line representing average, and green area representing the 90% reference range (10th percentile to 90th percentile).^[1]

It should match the fetus' gestational age in weeks within 1 to 3 cm, e.g., a pregnant woman's uterus at 26 weeks should measure 23 to 29 cm. This is valid from 24 weeks.

Most caregivers will record their patient's fundal height on every prenatal visit. Measuring the fundal height can be an indicator of proper fetal growth^[2] and amniotic fluid development.

Knowledge of gestational age may impact how the height is measured.^[3]

Shorter measure [edit]

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 pregnancy based on first day of last menstrual period
• Fetus is healthy but physically small
• Oligohydramnios
• Fetus positioned sideways
• Small for gestational age

Longer measure [edit]

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

• Twins, or other types of multiple birth
• Error in estimated date of conception
• Fetus is healthy but physically large
• Gestational diabetes causing a larger baby
• Polyhydramnios
• Large for gestational age
• Hydatidiform Mole
• Breech birth

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

References [edit]