Ultrasound technology is a standard tool used to monitor the development of the fetus. While the first ultrasound confirms the pregnancy, establishes the due date, and determines the number of fetuses, the second major ultrasound serves a far more comprehensive purpose. This scan shifts the focus from confirmation to conducting a detailed assessment of the developing baby and the support structures within the womb.
The Typical Timeline and Scheduling
The second major prenatal ultrasound is generally scheduled between 18 and 22 weeks of gestation. This specific window is chosen because the fetus has grown large enough for a detailed examination of its internal organs and physical structures. Earlier, structures might be too small to visualize clearly, potentially leading to missed findings.
Performing the scan within this timeframe also allows medical providers to act on any findings that may require follow-up testing or specialized consultations. While 18 to 22 weeks is the standard, the exact timing can be adjusted based on the patient’s medical history or if there is a known reason for a high-risk pregnancy. This scan is a part of routine screening offered to nearly all pregnant individuals.
Primary Goals of the Second Ultrasound
This examination is referred to as the “Anatomy Scan” or “Level 2 Ultrasound” because its objective is to evaluate the fetal anatomy in detail. The sonographer performs biometry, taking numerous measurements to assess the baby’s growth and confirm the gestational age. Standard measurements include the biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL).
A significant portion of the scan is dedicated to a systemic check of the baby’s major organ systems. The sonographer examines the four chambers of the heart and the major outflow tracts to screen for cardiac anomalies. They also look at the structure of the fetal brain, including the ventricles and cerebellum, and assess the spine for defects like spina bifida.
The kidneys, stomach, bladder, and limbs are all individually evaluated to ensure they are developing correctly and appear structurally normal. Beyond the baby’s body, the scan also focuses on the supporting structures within the uterus.
The location of the placenta is carefully mapped to check its relationship to the cervix, specifically looking for Placenta Previa, where the placenta covers the cervix. The sonographer assesses the amount of amniotic fluid surrounding the fetus, as both too much or too little fluid can indicate a potential issue. This detailed view of the external anatomy also allows for the optional determination of the baby’s sex.
What Happens After the Scan
Once imaging is complete, the sonographer may provide preliminary information, but the final, official results are reviewed by a radiologist or obstetrician. The healthcare provider will discuss the findings with the patient, usually at the next scheduled appointment, or sooner if immediate concerns are noted. Most results are normal, confirming that the baby is growing well and that the internal anatomy appears typical for the gestational age.
If the reviewing physician identifies an area that was difficult to visualize or an unexpected finding, they may recommend a follow-up growth scan or a specialized ultrasound. For instance, if heart views were limited, a fetal echocardiogram might be suggested, which focuses only on the baby’s heart structure and function.
Abnormal findings may also lead to a consultation with a maternal-fetal medicine specialist for further testing, such as blood work or an amniocentesis. Following the anatomy scan, prenatal care transitions toward the later stages of pregnancy. If the scan was normal, subsequent ultrasounds are less frequent and only performed if a specific medical need arises.