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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. Fundal height roughly corresponds to gestational age in weeks between 16 to 36 weeks for a vertex fetus. When a tape measure is unavailable, finger widths are used to estimate centimeter (week) deviations from a corresponding anatomical landmark. However, landmark distances from the pubic symphysis are highly variable depending on body type. In clinical practice, recording the actual fundal height measurement from the palpable top of the uterus to the superior edge of the pubic symphysis is standard practice beginning around 20 weeks gestation.
|Gestational age||Fundal height landmark|
|12 weeks||Pubic Symphysis|
|36 weeks||Xiphoid Process of Sternum|
|37-40 weeks||Regression of fundal height between 36-32 cm|
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.
Knowledge of gestational age may impact how the height is measured.
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
- Fetus positioned sideways
- 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
- Gestational diabetes causing a larger baby
- Large for gestational age
- Hydatidiform Mole
- Breech birth
As a pregnancy approaches its end, the fundal height will become less accurate.
- Morse K, Williams A, Gardosi J (December 2009). "Fetal growth screening by fundal height measurement". Best Pract Res Clin Obstet Gynaecol 23 (6): 809–18. doi:10.1016/j.bpobgyn.2009.09.004. PMID 19914874.
- Jelks A, Cifuentes R, Ross MG (October 2007). "Clinician bias in fundal height measurement". Obstet Gynecol 110 (4): 892–9. doi:10.1097/01.AOG.0000282758.28533.d9. PMID 17906025.