A fetal growth scan is a targeted ultrasound examination, typically performed in the third trimester, to assess the size and general well-being of the fetus. This specialized procedure uses sound waves to create images and measurements to estimate the baby’s weight and growth trajectory. Unlike routine screening, a dedicated growth scan is only performed when a healthcare provider needs specific information beyond standard prenatal checks. The total number of scans a patient receives varies, depending on individual health factors and the complexity of the pregnancy.
Standard Ultrasound Schedule Versus Dedicated Growth Scans
For a low-risk pregnancy, the medical standard typically involves two main ultrasound examinations, neither of which is a dedicated growth scan. The first is a dating scan, performed in the first trimester, primarily to confirm the due date using a measurement of the embryo or fetus. The second routine scan is the comprehensive anatomy assessment, which occurs around 18 to 22 weeks of gestation to check the baby’s development and organ structures.
A low-risk pregnancy may require zero dedicated growth scans, as standard monitoring is sufficient to track progress. A growth scan is specifically ordered when a clinical concern arises later in the pregnancy, usually after the anatomy scan. This often happens if the fundal height measurement is significantly larger or smaller than expected for the gestational age. The growth scan then serves as a diagnostic tool to investigate the discrepancy found during the routine physical examination.
Medical Indications Requiring Serial Growth Monitoring
Patients identified as having a moderate or high-risk pregnancy are the ones most likely to receive a series of growth scans. These repeated examinations are necessary to monitor the fetus closely for conditions that can impact its ability to thrive in the uterine environment. The schedule for these serial scans is typically set at two-to-four-week intervals to accurately track the rate of growth over time.
Maternal medical conditions represent a common reason for increased surveillance, including pre-existing diabetes, chronic high blood pressure, or a history of preeclampsia. These conditions can affect placental function, which is the organ responsible for delivering nutrients and oxygen to the baby. Previous complications, such as having a prior baby with Fetal Growth Restriction (FGR), also place a patient into a higher-risk category requiring frequent monitoring.
Fetal and uterine factors also necessitate a serial scanning schedule. Pregnancies involving twins or other multiples require regular checks because the shared environment raises the risk of growth discordance. If an initial scan detects a concern like low amniotic fluid volume (oligohydramnios) or if the estimated fetal weight falls below the tenth percentile, serial scans are initiated to guide clinical decisions. This repeated assessment provides timely data on the baby’s status so intervention, such as early delivery, can occur if the risks of remaining in utero outweigh the risks of prematurity.
Key Measurements Taken During a Fetal Growth Scan
The primary goal of the growth scan is to perform fetal biometry, which is the process of measuring specific body parts to estimate the baby’s size. The sonographer takes three main measurements: the Head Circumference (HC), the Abdominal Circumference (AC), and the Femur Length (FL). These measurements are then input into a formula to calculate the Estimated Fetal Weight (EFW), which is plotted on a customized growth chart to determine the baby’s percentile.
Beyond simple size, the scan also assesses several indicators of the baby’s well-being. The Amniotic Fluid Index (AFI) is measured to ensure a healthy amount of fluid surrounds the baby, as low levels can indicate placental issues. Specialized Doppler flow studies are performed, most commonly on the umbilical artery, to evaluate blood flow velocity. This analysis provides insight into how efficiently the placenta is supporting the fetus, which is important when growth concerns have been raised.