Fundal Height Calculator
Calculate fundal height quickly with our gynecology & pregnancy tool. Get results based on evidence-based formulas with clear explanations.
Reviewed by Rahul Singh, Health & Wellness Specialist
Formula
Expected Fundal Height (cm) = Gestational Age (weeks); EFW (g) = (FH - 12) x 155
After 20 weeks, fundal height in centimeters approximately equals gestational age in weeks, with a normal range of plus or minus 2 cm. The Johnson formula estimates fetal weight by subtracting 12 from the fundal height and multiplying by 155.
Worked Examples
Example 1: Normal Fundal Height at 30 Weeks
Problem:A woman at 30 weeks and 3 days gestation measures a fundal height of 31 cm. Her height is 168 cm. Is this within normal range?
Solution:Gestational age: 30 + 3/7 = 30.4 weeks\nExpected fundal height: 30.4 cm\nNormal range: 28.4 to 32.4 cm (30.4 +/- 2)\nMeasured: 31 cm\nDifference: 31 - 30.4 = +0.6 cm\nHeight adjustment: (168 - 165) x 0.1 = +0.3 cm\nAdjusted difference: 0.6 - 0.3 = +0.3 cm
Result:Assessment: Appropriate for gestational age | Difference: +0.6 cm | Within normal range
Example 2: Small Fundal Height Requiring Follow-up
Problem:A woman at 34 weeks gestation has a fundal height of 30 cm. Her height is 160 cm. Evaluate the measurement.
Solution:Expected fundal height: 34.0 cm\nNormal range: 32.0 to 36.0 cm\nMeasured: 30 cm\nDifference: 30 - 34 = -4.0 cm (below normal range)\nJohnson EFW: (30 - 12) x 155 = 2,790 g (6.1 lbs)\nHeight adjustment: (160 - 165) x 0.1 = -0.5 cm\nAdjusted difference: -4.0 - (-0.5) = -3.5 cm (still abnormal)
Result:Assessment: Small for gestational age | EFW: 2,790 g | Ultrasound recommended to rule out IUGR
Frequently Asked Questions
What is fundal height and how is it measured?
Fundal height is the distance measured in centimeters from the pubic bone (symphysis pubis) to the top of the uterus (uterine fundus). It is measured using a flexible tape measure with the pregnant woman lying supine with a partially empty bladder. The healthcare provider locates the top of the uterus by palpation and measures straight down to the top of the pubic bone. This measurement is typically taken at each prenatal visit after 20 weeks of gestation and recorded on a growth chart. Fundal height serves as a simple, non-invasive screening tool to monitor fetal growth and detect potential complications such as growth restriction or excessive growth.
How does fundal height correlate with gestational age?
After 20 weeks of pregnancy, fundal height in centimeters approximately equals the gestational age in weeks, give or take about 2 centimeters. This relationship, known as the McDonald rule, provides a quick clinical estimate of fetal growth. For example, at 28 weeks gestation the expected fundal height would be approximately 26 to 30 centimeters. Before 20 weeks, the uterus is still within the pelvis and fundal height measurements are less reliable. The correlation is strongest between 24 and 36 weeks, after which fetal engagement in the pelvis can cause the measurement to plateau or even decrease slightly. Individual variation exists due to maternal body habitus, fetal position, and amniotic fluid volume.
What does it mean if fundal height is larger than expected?
A fundal height measurement more than 2 centimeters above the expected value for gestational age may indicate several conditions requiring further evaluation. The most common causes include fetal macrosomia (a larger than average baby), polyhydramnios (excess amniotic fluid), multiple gestation (twins or more), or incorrect pregnancy dating. Maternal factors such as obesity, a full bladder during measurement, or uterine fibroids can also falsely elevate fundal height readings. When a large fundal height is detected, the typical next step is an ultrasound to assess fetal size, amniotic fluid volume, and confirm gestational dating. Gestational diabetes screening may also be recommended if not already completed, as uncontrolled blood sugar can lead to fetal overgrowth.
What does a smaller than expected fundal height indicate?
A fundal height measurement more than 2 centimeters below expected for gestational age raises concern for intrauterine growth restriction (IUGR), which means the fetus may not be growing at the expected rate. Other possible explanations include oligohydramnios (too little amniotic fluid), a transverse or oblique fetal lie, fetal engagement deep in the pelvis, or a slender maternal build. Incorrect gestational dating is also a common cause of apparent size discrepancy. When small fundal height is identified, ultrasound evaluation is performed to assess fetal biometry, estimated weight, amniotic fluid index, and placental function. Serial monitoring with Doppler studies of umbilical artery blood flow may be recommended if growth restriction is confirmed.
References
Reviewed by Rahul Singh, Health & Wellness Specialist · Editorial policy