An ultrasound, or sonogram, is a widely used diagnostic tool in prenatal care that relies on high-frequency sound waves to generate real-time images of the developing fetus. This non-invasive procedure allows healthcare providers to visualize the pregnancy, monitor fetal growth, and assess the health of the mother and baby. The frequency of scans is primarily determined by medical necessity, following established guidelines for an uncomplicated gestation. The typical schedule provides a framework for monitoring a healthy pregnancy from the first trimester onward.
Routine Ultrasounds: The Standard Schedule
For individuals experiencing a low-risk, uncomplicated pregnancy, the standard schedule typically includes two main ultrasounds. The first is the dating scan, generally performed in the first trimester between the 7th and 14th week of gestation. This initial evaluation establishes the pregnancy timeline.
The second routine scan is the comprehensive anatomy survey, which occurs during the second trimester. This detailed examination is usually scheduled between the 18th and 22nd week of pregnancy. If both major scans are normal and the mother’s clinical assessment remains within expected parameters, further ultrasounds are typically not required.
Defining the Purpose of Key Scans
The first-trimester dating scan primarily establishes an accurate estimated due date (EDD). This is achieved by measuring the fetus from the crown to the rump, known as the Crown-Rump Length (CRL), which is the most precise dating method early in pregnancy. The scan also confirms viability by detecting a fetal heartbeat and verifies the location of the pregnancy to rule out complications like an ectopic pregnancy. This early assessment also identifies if the patient is carrying multiples, which changes the course of prenatal care.
The second-trimester anatomy scan is a comprehensive structural evaluation of the fetus. Its main goal is to screen for structural abnormalities by systematically examining major organ systems, including the heart, brain, spine, kidneys, and limbs. The technician also assesses the volume of amniotic fluid, which indicates fetal well-being. Another objective is determining the location of the placenta to check for conditions like placenta previa, where the placenta may cover the cervix.
When Additional Scans Are Medically Necessary
The number of ultrasounds increases when specific maternal or fetal conditions require closer medical supervision. These additional scans are often ordered to monitor fetal growth and blood flow, watching for complications that can develop later in the pregnancy. A common reason for increased surveillance is a pre-existing maternal condition, such as chronic high blood pressure, preeclampsia, or gestational diabetes. These conditions can affect placental function and, consequently, the baby’s growth.
Fetal concerns are another indicator for more frequent imaging, particularly if a previous scan suggested a potential issue. For example, serial ultrasounds track growth velocity if a fetus is suspected to be small or large for gestational age. Complications like a low-lying placenta identified during the anatomy scan may require a follow-up third-trimester scan to confirm placental movement. Patients carrying multiple fetuses also receive regular scans to monitor the growth and development of each baby.
Safety Profile and Elective Ultrasounds
Diagnostic ultrasound is considered a safe imaging modality because it uses high-frequency sound waves rather than ionizing radiation. Medical professionals adhere to the ALARA principle (“As Low As Reasonably Achievable”). This means the power and duration of the sound waves are minimized during the scan. There is no evidence that diagnostic ultrasound, when used prudently by trained personnel, causes harm to the fetus.
Elective ultrasounds, such as those providing 3D or 4D images for souvenir purposes, are distinct from medically justified diagnostic scans. Although they use the same technology, they are performed solely for non-medical reasons and often involve longer exposure times to obtain high-quality images. Medical organizations advise against the excessive use of ultrasound for non-diagnostic purposes. The procedure should only be performed when there is a valid clinical indication.