An ultrasound, often called a sonogram, is a non-invasive medical imaging technique that uses high-frequency sound waves to create real-time pictures of the inside of the body. This technology is a standard component of prenatal care, allowing providers to safely monitor fetal development and the health of the pregnancy. The procedure involves applying a transducer to the abdomen (or sometimes internally in early pregnancy) to send and receive sound waves that are converted into images. Understanding the typical schedule of these scans clarifies their role in monitoring fetal well-being and managing the pregnancy.
The Standard Sonogram Schedule
For a low-risk and uncomplicated pregnancy, the standard protocol involves a minimum of two sonograms. This ensures essential diagnostic information is gathered at opportune times during gestation. The first routine scan is typically performed during the first trimester, usually between weeks 7 and 13. The second comprehensive ultrasound is scheduled for the second trimester, usually between 18 and 22 weeks. This timing allows the fetus to be sufficiently developed for a detailed anatomical assessment. If issues are identified or additional information is required, the total number of scans will increase beyond this standard two-scan minimum.
Purpose of Each Routine Scan
The first-trimester scan, often called a dating or viability scan, serves several diagnostic purposes. Its primary goal is to confirm the presence of a fetal heartbeat, which confirms viability. The scan also accurately determines gestational age by measuring the crown-rump length (CRL), establishing the estimated due date.
This early sonogram is also crucial for confirming the pregnancy is implanted correctly within the uterus, ruling out an ectopic pregnancy. The scan identifies the number of fetuses present, confirming whether the patient is carrying a single baby or multiples. Performing this scan early sets the foundational data for subsequent prenatal monitoring.
The second routine procedure, known as the anatomy scan, is a comprehensive evaluation performed around the halfway point of the pregnancy. This detailed assessment systematically examines all major fetal organ systems (including the brain, heart, spine, kidneys, and limbs) to screen for structural abnormalities. Measurements of the fetal head circumference, abdominal circumference, and femur length are taken to confirm healthy growth and development.
The anatomy scan also evaluates the maternal structures that support the pregnancy. The location of the placenta is mapped to check for conditions like placenta previa, where the placenta covers the cervix, which affects delivery planning. The volume of amniotic fluid is also assessed, as too much or too little fluid can indicate potential complications.
Medically Indicated Scans
Many pregnancies require additional sonograms beyond the standard two due to specific medical necessities or risk factors. These non-routine scans are ordered when a provider needs to closely monitor a suspected issue or a pre-existing maternal condition. Conditions such as diabetes, chronic hypertension, or advanced maternal age may necessitate more frequent monitoring.
Specific symptoms or findings can also trigger the need for extra scans, such as vaginal bleeding, abdominal pain, or a fundal height measurement inconsistent with the estimated gestational age. If the anatomy scan identifies a low-lying placenta, a follow-up growth scan is often scheduled in the third trimester to check if the placenta has moved away from the cervix.
Specialized Third Trimester Scans
For concerns about fetal growth, a specialized growth ultrasound is used to measure the baby’s size and estimate its weight. In the third trimester, a biophysical profile (BPP) may be performed. The BPP combines an ultrasound assessment of fetal movement, breathing, tone, and amniotic fluid volume with a non-stress test. These procedures ensure that appropriate interventions can be planned for pregnancies that deviate from the low-risk standard.