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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.
|Gestational age||Fundal height|
|40 weeks||1-2 finger widths below subcostal arch|
|36 weeks||At costal arch|
|32 weeks||Between umbilicus and xiphoid process|
|28 weeks||3 finger widths above umbilicus|
|24 weeks||At umbilicus|
|20 weeks||3 finger widths below umbilicus|
|16 weeks||3 finger widths above symphysis|
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 and amniotic fluid development.
Knowledge of gestational age may impact how the height is measured.
Shorter measure 
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
Longer measure 
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.
- White LJ, Lee SJ, Stepniewska K, et al. (March 2012). "Estimation of gestational age from fundal height: a solution for resource-poor settings". J R Soc Interface 9 (68): 503–10. doi:10.1098/rsif.2011.0376. PMC 3262426. PMID 21849388.
- 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.