Fundal height is a simple, non-invasive measurement used during prenatal check-ups to track the progress of a pregnancy. It is defined as the distance, measured in centimeters, from the top of the pregnant uterus (the fundus) down to the top edge of the pubic bone (symphysis pubis). This routine screening tool monitors the overall growth of the baby and the uterus throughout the second and third trimesters, providing a quick estimate of how the pregnancy is progressing compared to the expected timeline.
Why Fundal Height is Measured and When It Begins
The primary purpose of measuring fundal height is to consistently track the baby’s growth rate over time, offering an indication of fetal well-being. Healthcare providers use this measurement at each visit to assess if the growth trajectory is consistent with the gestational week. Fundal height is not a precise diagnostic tool, but a simple method to screen for potential deviations from the expected growth pattern.
Measurement typically begins around the 20th week of gestation because the uterus is usually located too low within the pelvis for accurate external measurement before this time. By 20 weeks, the top of the uterus generally reaches the level of the belly button, making it readily accessible. For the second and early third trimesters, the fundal height measurement in centimeters should approximately match the number of weeks of gestation.
For example, a person 24 weeks pregnant would typically measure about 24 centimeters, plus or minus a few centimeters. This correspondence usually holds true until about 36 weeks of pregnancy. Consistent measurement helps confirm the accuracy of the estimated due date and provides reassurance about the baby’s steady development.
How the Measurement is Taken
The measurement of fundal height is a straightforward procedure performed during a routine prenatal examination. The pregnant person is asked to lie flat on their back to allow the practitioner clear access to the abdomen. It is recommended that the bladder be emptied beforehand, as a full bladder can alter the measurement by several centimeters.
The practitioner identifies two anatomical landmarks: the top of the pubic bone and the top of the uterus (the fundus). They use a flexible measuring tape to find the vertical distance between these points. The tape is placed with the zero mark at the upper border of the pubic bone and stretched over the curve of the abdomen to the highest palpable point of the uterus.
The distance is recorded in centimeters and charted to monitor the progression of growth throughout the pregnancy. Temporary factors, such as the baby’s position or the amount of amniotic fluid, can influence the reading on any given day. Therefore, the overall trend of the measurements over time is more informative than a single number.
What the Measurements Indicate
A fundal height measurement within two to three centimeters of the expected gestational week is considered within the normal range. When the measurement falls outside this expected range, it is flagged as a deviation. This deviation prompts further investigation but is not a definitive diagnosis, suggesting the pregnancy requires a closer look to understand the discrepancy.
Measurement is Larger Than Expected
A fundal height reading larger than expected may be due to several factors. A common cause is an incorrect initial dating of the pregnancy, meaning the person is further along than previously thought. The larger measurement could also be caused by carrying multiples, such as twins or triplets, or by a higher volume of amniotic fluid (polyhydramnios). Other possibilities include the presence of uterine fibroids or a baby that is larger than average.
Measurement is Smaller Than Expected
A fundal height that measures smaller than expected may stem from an inaccurate initial dating of the pregnancy. The baby may be positioned low in the pelvis, or the person may have a smaller body frame or strong abdominal muscles, which can affect the reading. More medically relevant causes include restricted growth of the baby inside the uterus (intrauterine growth restriction, or IUGR). Another cause is having too little amniotic fluid, a condition called oligohydramnios.
When a deviation of more than two or three centimeters is noted, the next step is to utilize more precise diagnostic tools. An ultrasound is ordered to confirm the gestational age, assess the amniotic fluid levels, and measure the baby’s size and growth rate. Many fundal height deviations are common and often resolve without serious issues once a more accurate picture is obtained.