Fundal height (FH) measurement is a routine procedure used in prenatal care to monitor the growth and development of the fetus. It is defined as the distance, measured in centimeters, from the top of the pubic bone to the highest point of the uterus, known as the fundus. This simple physical measurement provides a quick, non-invasive way to estimate gestational age and assess if the fetus is growing as expected. The measurement generally begins around the 20th week of gestation and becomes a standard part of subsequent prenatal visits.
Why Fundal Height is Measured
The primary purpose of measuring fundal height is to serve as an initial screening tool for assessing the rate of fetal growth. A measurement that aligns with the gestational age suggests the pregnancy is progressing along a typical trajectory, and regular tracking helps establish a growth curve. Monitoring the fundal height helps identify potential deviations that may warrant further investigation, such as an ultrasound. For instance, a consistently smaller measurement may suggest restricted fetal growth (IUGR) or a reduced volume of amniotic fluid (oligohydramnios). Conversely, a larger measurement could indicate conditions like excessive amniotic fluid (polyhydramnios) or a multiple gestation pregnancy. This measurement is a cost-effective method to ensure timely intervention if a complication is suspected.
Anatomical Landmarks and Preparation
Accurate fundal height measurement relies on identifying two fixed anatomical points: the symphysis pubis and the uterine fundus. The symphysis pubis is the firm joint located at the top center of the pubic bone, which serves as the starting point for the measurement. The patient must lie flat on their back (supine), sometimes with a slight tilt to prevent compression of major blood vessels. A preparatory step involves ensuring the patient’s bladder is empty, as a full bladder can push the uterus upward and skew the final measurement. The location of the fundus changes predictably; by 12 weeks, it is palpable above the symphysis pubis, and by 20 to 22 weeks, it generally reaches the level of the umbilicus.
Step-by-Step Technique for Locating the Fundus
Locating the fundus, the curved top edge of the uterus, requires careful external palpation across the abdomen. The process begins with the healthcare provider placing one hand gently on the lower abdomen near the symphysis pubis. They then slowly sweep the hand upward, applying light but firm pressure to feel for the firm, rounded resistance of the uterine wall. The fundus feels distinctly different from the softer surrounding abdominal tissue, presenting as a distinct, firm border. Once the highest point is located, a flexible, non-stretch tape measure is used, ensuring the measurement is taken along the longitudinal axis of the uterus.
The measurement process involves placing the zero end of the tape measure precisely at the superior edge of the symphysis pubis. The tape is then extended over the curve of the abdomen to the identified top of the fundus, following the natural curve of the body. The resulting distance is read and recorded in centimeters.
What the Measurements Indicate
The resulting fundal height measurement is compared against the number of weeks of gestation, particularly between 20 and 36 weeks. During this period, the measurement in centimeters should roughly equal the gestational age in weeks, often referred to as the “cm = weeks” rule. A measurement that falls within two to three centimeters above or below the expected value is generally considered within the normal range for growth. Significant deviations from this expected range, such as measuring three or more centimeters outside the norm, may prompt additional evaluation. Common reasons for slight variations often include maternal body build, the specific position of the fetus, or the amount of amniotic fluid present.
A substantially smaller measurement can signal conditions like intrauterine growth restriction (IUGR), while a significantly larger measurement may suggest polyhydramnios or the presence of twins. If a deviation is noted, an ultrasound is typically ordered to obtain a more precise assessment of fetal size, well-being, and amniotic fluid volume.