A growth ultrasound is a non-invasive medical imaging procedure used late in pregnancy to monitor the development and overall well-being of the fetus. This scan utilizes high-frequency sound waves to create real-time images of the baby, the placenta, and the surrounding amniotic fluid. It is a common and safe diagnostic tool that provides healthcare providers with important data to ensure the pregnancy is progressing as expected. The information gathered during this assessment helps in making informed decisions about the remainder of the pregnancy and the timing of delivery.
The Typical Duration of the Appointment
The actual scanning portion of a growth ultrasound typically takes between 20 and 40 minutes. This range accounts for the time a sonographer needs to acquire several precise images and measurements of the developing fetus. The total time spent at the clinic or hospital, however, is generally longer, often requiring an appointment window of up to 90 minutes. This extended period includes necessary steps like check-in, waiting time, and a consultation with the healthcare provider to discuss the findings immediately after the scan.
Several factors can influence the duration of the scan and how long the sonographer needs to complete it successfully. If the baby is not in an ideal position for measurement, the sonographer may ask the mother to change position or take a short walk to encourage fetal movement. A higher maternal body mass index or a reduced amount of amniotic fluid can also make it more challenging to obtain clear images, potentially extending the procedure. The presence of twins or other multiples will naturally increase the time required, as each fetus needs a complete set of measurements.
Purpose and Timing of the Scan
A growth scan is primarily ordered to check the baby’s growth trajectory and estimate its current weight, which is particularly relevant in the third trimester of pregnancy. This procedure helps to identify if the fetus is growing too slowly, a condition known as fetal growth restriction, or if it is growing too large, which can be a concern for conditions like gestational diabetes. The scan also assesses the health of the placenta and the volume of amniotic fluid, both of which are indirect indicators of fetal well-being.
The timing of the growth scan is usually determined by the presence of specific risk factors or clinical concerns. For high-risk pregnancies, such as those involving maternal hypertension or diabetes, serial growth scans may begin as early as the late second trimester, around 28 weeks. For low-risk pregnancies, a scan may be ordered later in the third trimester, commonly between 32 and 36 weeks, often if the fundal height measurement taken by the midwife or doctor suggests the baby is smaller or larger than expected. Regular monitoring is implemented when there is a risk of impaired nutrient and oxygen delivery from the placenta.
Key Measurements Taken During the Exam
To determine the Estimated Fetal Weight (EFW), the sonographer captures specific biometric measurements from the fetus. These measurements are crucial for calculating the baby’s size and plotting its growth trajectory.
Biometric Measurements
- Head Circumference (HC): Taken from a cross-sectional view of the fetal skull.
- Biparietal Diameter (BPD): The measurement across the widest part of the head, often taken simultaneously with the HC.
- Abdominal Circumference (AC): Measured from a circular cross-section of the abdomen, this is considered one of the most sensitive indicators of fetal size and weight because it reflects the baby’s soft tissue development.
- Femur Length (FL): Provides a measurement of the baby’s long bone growth.
These four measurements—HC, BPD, AC, and FL—are inputted into a specialized computer algorithm to calculate the EFW, which is then plotted on a growth curve specific to the gestational age. The assessment also includes a check of the amniotic fluid volume, often by measuring the deepest pocket of fluid, and a Doppler study of the umbilical artery blood flow to gauge placental function. While the EFW is an approximation, it typically estimates the baby’s actual birth weight within a 10 to 15 percent margin.
Preparation and Next Steps
Preparation for a growth ultrasound is generally simple, often requiring no special restrictions. Unlike earlier pregnancy scans, a full bladder is usually not needed for a third-trimester growth scan, as the uterus is large enough to be easily imaged through the abdomen. Wearing comfortable, loose-fitting clothing that allows easy access to the abdomen is helpful, as the sonographer will need to apply ultrasound gel directly to the skin.
Once the scan is complete, the sonographer will finalize the measurements and generate the report. The next step involves a review of these results, often discussed with the patient by the referring obstetrician or midwife shortly after the procedure. If the scan reveals a slow-growth pattern or an issue with the amniotic fluid or blood flow, the healthcare team will develop an individualized plan for closer follow-up. This plan may involve scheduling serial growth scans more frequently to monitor changes over time, or it may lead to discussions regarding the optimal timing and method of delivery.