A prenatal ultrasound, also known as a sonogram, is a non-invasive imaging technique that uses high-frequency sound waves to create live images of a fetus. It is a standard component of modern prenatal care, offering a safe way to monitor the pregnancy. The images help assess fetal growth, examine the placenta, and check the mother’s reproductive organs.
The Standard Prenatal Ultrasound Schedule
For a low-risk, healthy pregnancy, the standard prenatal schedule typically includes one or two ultrasounds. The exact number can vary based on the healthcare provider’s preference and specific guidelines. Most pregnant individuals undergo at least one comprehensive scan during the middle of the pregnancy.
The first routine scan is usually offered in the first trimester, between 10 and 14 weeks of gestation. This early scan is often used to establish the estimated due date. The second and most comprehensive scan is routinely scheduled between 18 and 22 weeks of pregnancy.
Key Functions of Routine Ultrasounds
The initial routine ultrasound, often called the dating or viability scan, confirms the pregnancy and determines the gestational age. Measuring the crown-rump length provides the most precise estimate for the due date. This scan also confirms the presence of a fetal heartbeat, checks for multiple gestations, and ensures the pregnancy is located within the uterus.
The second routine scan, known as the anatomy or anomaly scan, offers a detailed evaluation of the fetal structure. This comprehensive examination screens for developmental issues by checking the baby’s organs, limbs, face, and spine. The sonographer also assesses the volume of amniotic fluid, the location of the placenta, and the umbilical cord to ensure adequate support for the fetus.
Reasons for Additional Monitoring Scans
The number of ultrasounds increases beyond the standard schedule if the pregnancy is considered high-risk or if complications arise. Maternal health conditions, such as pre-existing diabetes, chronic hypertension, or advanced maternal age, often necessitate more frequent monitoring. These scans help track how the fetus is responding to the mother’s condition, particularly regarding growth.
Specific concerns during pregnancy may prompt additional scans. These include unexplained bleeding, a discrepancy in fundal height measurements, or previous complications like preterm birth. If the initial anatomy scan was incomplete, a follow-up scan may be required to fully visualize all structures.
Pregnancies involving multiples require significantly more frequent ultrasounds to monitor the growth and development of each fetus. If conditions like fetal growth restriction or placental issues are identified, the healthcare team will order regular biophysical profiles or Doppler flow studies. These monitoring scans ensure timely intervention if the baby’s health deteriorates.
Understanding Ultrasound Safety
Diagnostic ultrasound is considered a safe imaging modality because it does not use ionizing radiation. The technology relies on sound waves, and decades of clinical use have not shown any definitive link between diagnostic ultrasound and adverse effects. Healthcare professionals adhere to the principle of “As Low As Reasonably Achievable” (ALARA) to minimize acoustic energy and exposure time during each scan.
The ALARA principle guides sonographers to use the lowest power setting and shortest duration necessary to obtain diagnostic information. It is important to distinguish these medically indicated scans from non-medical, elective keepsake scans, such as 3D or 4D imaging. Elective scans may involve longer exposure times and are performed without medical necessity, which is generally discouraged by professional medical bodies.