The growth of the abdomen is a visible sign of a developing pregnancy. In a clinical setting, measuring the size of the “belly bump” is a routine, non-invasive method used to monitor the overall growth of the uterus. This measurement provides an estimate of fetal development and tracks the progression of the pregnancy. Monitoring uterine growth is a simple screening tool to confirm the fetus is growing at an expected rate.
Fundal Height Measurement: The Standard Clinical Approach
The standardized method for assessing uterine growth is the fundal height measurement. This technique measures the distance from a fixed point on the pelvis to the top of the uterus, known as the fundus. Providers typically begin taking this measurement at prenatal visits starting around the 20th week of gestation.
Before the measurement, the patient lies in a semi-recumbent position, often with an empty bladder, since a full bladder can inflate the measurement. The provider first locates the symphysis pubis, the firm joint at the top of the pubic bone, which serves as the lower boundary.
Next, the provider gently palpates the abdomen to locate the fundus, the uppermost part of the uterus. Once both landmarks are identified, a flexible tape measure is used to determine the distance between them. The tape is stretched along the curve of the abdomen from the symphysis pubis to the top of the fundus.
The resulting distance is recorded in centimeters and tracked throughout the pregnancy. Fundal height offers an efficient, low-cost way to screen for potential growth concerns. This allows for early detection and further investigation if necessary.
Understanding Your Measurements
Fundal height is interpreted using a guideline that correlates the measurement in centimeters with the weeks of gestation. Between 20 and 36 weeks, the measurement in centimeters is expected to roughly match the number of weeks pregnant. For example, a person 28 weeks pregnant would typically measure about 28 centimeters.
This correlation is used as a screening tool, not a precise diagnostic measure. A measurement is considered normal if it falls within an acceptable range, generally plus or minus two to three centimeters from the gestational week. For instance, a fundal height of 25 centimeters at 28 weeks is often within the expected variation.
The value of this measurement lies in observing the pattern of growth over time, not just a single reading. Providers plot these measurements on a growth chart to ensure the uterus maintains a steady trajectory of expansion. A consistent growth trend within the normal range suggests the fetus is developing as anticipated.
When Measurements Deviate from Expectations
When fundal height falls significantly outside the expected range, either too large or too small, it signals the need for further investigation. A discrepancy of more than three centimeters from the gestational week often prompts additional screening. A single outlying measurement does not automatically indicate a serious problem, but suggests that more information is needed.
A larger-than-expected measurement may be due to carrying multiple fetuses, a large amount of amniotic fluid (polyhydramnios), or the fetus being positioned high in the uterus. Conversely, a smaller measurement could indicate restricted fetal growth, low amniotic fluid volume, or the fetus descending into the pelvis for birth. The accuracy of the estimated due date can also affect the measurement.
In these situations, the provider typically orders a diagnostic ultrasound. The ultrasound provides a precise assessment of fetal size and weight, measures amniotic fluid volume, and confirms the baby’s position. This follow-up testing helps distinguish between simple variations and actual concerns, ensuring the pregnancy is properly monitored.