Fundal height measurement is an assessment used during prenatal care to monitor the progress of a pregnancy. This technique involves measuring the size of the pregnant uterus to evaluate fetal growth. It serves as a screening tool for healthcare providers during the second and third trimesters of pregnancy, providing an estimate of fetal development and verifying gestational progress.
What Fundal Height Represents in Pregnancy
Fundal height is the distance, measured in centimeters, from the top of the pubic bone to the highest point of the uterus, known as the fundus. This measurement reflects the vertical growth of the uterus as the fetus, placenta, and amniotic fluid increase in volume. It offers a rapid, cost-effective way for practitioners to track the expansion of the womb. The utility of this measurement lies in its ability to serve as an initial screening tool for potential growth concerns. By tracking this distance over serial prenatal visits, providers can quickly determine if the baby is growing at an expected rate compared to the established gestational age. Fundal height is not a diagnostic tool, but rather a preliminary indicator that may prompt further, more detailed testing if the results are outside the expected range.
Procedure for Measuring Fundal Height
The measurement process is standardized and performed by a medical professional during a prenatal visit, typically beginning around 20 weeks of gestation. The procedure starts with the mother lying on her back in a semi-reclined position to ensure the uterus is optimally positioned for measurement. It is recommended that the bladder be emptied prior to the measurement, as a full bladder can artificially inflate the result by several centimeters.
The healthcare provider first uses their hands to locate the two fixed anatomical landmarks required for the measurement. The starting point is the symphysis pubis, the firm, fixed cartilage joint located between the pubic bones. The endpoint is the fundus, the highest palpable point of the uterus.
A flexible, metric tape measure is then used to determine the distance between these two points. The tape is secured at the top of the pubic bone and stretched across the curve of the abdomen to the top of the fundus, following the longitudinal axis of the uterus. The resulting measurement, recorded in centimeters, is the fundal height, which is then plotted on a growth chart to monitor the progression of the pregnancy over time.
Understanding Your Fundal Height Results
The general rule for interpreting fundal height is based on a correlation that develops after the 20th week of pregnancy. From this point until approximately 36 weeks, the measurement in centimeters should roughly align with the number of weeks of gestation. For example, a woman who is 28 weeks pregnant would typically have a fundal height measurement of approximately 28 centimeters. A measurement is generally considered a significant deviation if it is more than two to three centimeters larger or smaller than the number of weeks of pregnancy.
Low Fundal Height
If the measurement is consistently low, it may suggest the baby is smaller than expected, possibly indicating intrauterine growth restriction or a lower-than-average volume of amniotic fluid (oligohydramnios). It could also simply mean the due date was miscalculated or the baby has begun to descend into the pelvis in preparation for birth.
High Fundal Height
Conversely, a fundal height measurement that is consistently high may signal a larger-than-average baby, a possible multiple gestation (like twins), or an excess of amniotic fluid (polyhydramnios).
Because fundal height is a screening tool, any significant deviation does not automatically confirm a problem. Instead, the finding prompts the healthcare provider to order more precise diagnostic testing, such as an ultrasound, to investigate the cause of the unusual measurement.
When Fundal Height May Not Reflect Gestational Age
Several physiological and situational factors can affect the accuracy of the fundal height measurement, making it an unreliable estimate of gestational age or fetal size.
These factors include:
- Maternal body mass index (BMI), where a higher BMI may cause the measurement to be inaccurately large.
- The presence of uterine fibroids, which are benign growths in the uterus, causing the measurement to be larger than expected.
- The baby’s position inside the uterus (e.g., transverse or breech presentation), which can alter the vertical measurement.
- The stage of pregnancy, as measurements become less accurate after 36 weeks when the baby drops lower into the pelvis (engagement).
- Variations in amniotic fluid volume, whether too much or too little, which directly influence the size of the uterus.