Fundal height is a measurement used to estimate the gestational age of a foetus/baby. MacDonald's Rule is one tool that can be employed once fundal height has been measured, however many units across the country are now using Customized Growth Charts which do not accept MacDonalds rule as being particularly accurate. Fundal height is a measure of the size of the uterus, 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 other types of multiple birth
• 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.
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 and amniotic fluid development.

Fundal Height is not considered to be a very accurate measurement to determine baby's weight. Ultrasound is far more accurate but still has a margin for error.

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