Fundal height measurement is a routine, non-invasive procedure in prenatal care used to track the growth of the uterus during pregnancy. Starting in the second trimester, this technique provides a quick estimate of fetal development. By monitoring the uterus’s upward movement, healthcare providers can screen for potential irregularities in fetal growth or the volume of amniotic fluid. Tracking the fundus’s position helps determine if the pregnancy is progressing along a typical timeline.
Understanding the Anatomical Landmarks
Fundal height measurement relies on two specific points on the pregnant abdomen. The first is the symphysis pubis, the joint connecting the pubic bones at the bottom of the pelvis, which serves as the consistent starting point.
The second point is the fundus, the uppermost, rounded portion of the uterus. As pregnancy advances, the uterus expands and the fundus rises higher into the abdominal cavity. The fundal height measurement is the distance, measured in centimeters, from the top of the symphysis pubis to the top of the uterine fundus.
The umbilicus, or belly button, is a naturally occurring landmark used as a rough reference point during the second trimester. Although its exact position varies slightly, it provides a general anatomical guide for assessing uterine size. The measurement is taken with the pregnant person lying on their back, using a flexible tape measure.
The Gestational Timeline of Uterine Growth
The uterus undergoes a predictable pattern of growth that allows providers to estimate gestational progress. The fundus becomes palpable just above the pubic bone around 12 weeks of gestation. By approximately 16 weeks, the fundus is typically situated halfway between the pubic bone and the umbilicus.
The fundus is generally expected to reach the level of the umbilicus around 20 to 22 weeks of gestation, marking the approximate halfway point of the pregnancy. When the fundus is measured above the umbilicus, it signifies that the pregnancy has progressed past this mid-point. The uterus continues its upward expansion into the abdomen until it reaches its maximum height.
The fundus reaches its maximum height near the bottom of the rib cage, or xiphoid process, around 36 weeks. Between 20 and 36 weeks, the fundal height in centimeters should correspond closely to the number of weeks of gestation, with an allowance of plus or minus two to three centimeters. For instance, a person at 28 weeks would typically have a fundal height measurement between 25 and 31 centimeters.
Purpose of Measuring Fundal Height
The primary role of fundal height measurement is to act as a simple screening tool to monitor overall fetal growth. By tracking the measurement over multiple prenatal visits, providers establish a growth pattern unique to the pregnancy. A steady, consistent increase suggests that the fetus is growing appropriately.
This measurement also provides an indirect assessment of the total volume inside the uterus, including the amniotic fluid, the fetus, and the placenta. It helps verify the accuracy of the estimated due date, especially when compared to early ultrasound data.
Tracking fundal height helps identify a trajectory of growth rather than relying on a single static measurement. If the measurement follows a normal curve, it offers reassurance that the pregnancy is progressing as expected.
When Measurements Deviate from the Norm
A fundal height measurement that is significantly higher or lower than expected for the gestational age indicates a need for further investigation, not an immediate diagnosis.
A measurement that is larger than anticipated—meaning the fundus is substantially higher than the umbilicus earlier than expected—can have several explanations. These include carrying more than one baby (such as twins) or having an excessive amount of amniotic fluid, a condition known as polyhydramnios.
The measurement may also be larger if the baby is positioned in a way that pushes the fundus higher, or if the baby is physically large (fetal macrosomia). Other causes include inaccurate initial dating of the pregnancy or the presence of uterine fibroids that increase the overall size of the uterus.
Conversely, a fundal height that is notably smaller than expected may indicate restricted fetal growth, often termed intrauterine growth restriction (IUGR). A lower-than-expected measurement can also be caused by having too little amniotic fluid (oligohydramnios).
The baby may be smaller than average for genetic reasons, or the measurement could be influenced by maternal factors, such as body type or the baby dropping lower into the pelvis before labor. In either case, a significant deviation from the expected range usually prompts a provider to recommend a more precise assessment, such as an ultrasound, to determine the underlying cause.