A pregnancy ultrasound is a non-invasive imaging technique that uses high-frequency sound waves to create images of the developing fetus and the mother’s reproductive organs. This procedure is a standard component of prenatal care, used to assess fetal health, growth, and development. The number of scans a patient receives varies significantly depending on their medical history and the clinical needs that arise during gestation.
The Typical Routine: Standard Scans and Their Timing
For a patient experiencing an uncomplicated, low-risk pregnancy, the standard protocol usually involves two ultrasounds. These two examinations are strategically timed to gather specific developmental and anatomical information about the fetus. This schedule serves as the foundation for prenatal monitoring, offering a baseline assessment of the pregnancy’s progression.
The first routine scan, often called the dating or viability scan, typically occurs in the first trimester, generally between six and twelve weeks. The primary purpose of this early visit is to confirm the presence of a fetal heartbeat, which indicates a viable pregnancy. Measuring the crown-rump length of the embryo at this stage is the most accurate method for determining gestational age and establishing a precise estimated due date. This initial scan also checks for the presence of multiple fetuses, such as twins or triplets.
The second standard scan is the comprehensive fetal anatomy survey, which is performed in the second trimester, usually between 18 and 22 weeks. Sometimes referred to as a Level 2 scan, this is a detailed examination of the fetus’s entire anatomy, including the brain, heart, kidneys, and limbs, to screen for structural development. During this scan, the technician also assesses the location of the placenta, measures the volume of amniotic fluid, and takes biometric measurements to evaluate fetal growth.
Reasons for Increased Monitoring
When risk factors or clinical concerns are present, the number of ultrasounds increases beyond the standard two to ensure closer observation of maternal and fetal well-being. These additional scans are medically indicated when a health provider suspects a potential issue or when a patient has pre-existing conditions that affect the pregnancy, such as diabetes or hypertension.
Serial Growth Checks
Fetal concerns often necessitate serial growth checks, which may begin around 28 to 32 weeks and are repeated every two to four weeks until delivery. This monitoring is used when a fetus is suspected of being too small or too large for gestational age, such as in cases of intrauterine growth restriction. The frequent measurements track the fetal growth velocity over time.
Biophysical Profile (BPP)
Specific third-trimester scans, like the biophysical profile, are employed to assess fetal status in higher-risk situations, such as when a patient is past their due date or reports decreased fetal movement. The BPP uses ultrasound to evaluate five parameters: fetal breathing movements, body movements, muscle tone, the amount of amniotic fluid, and a separate non-stress test that monitors the fetal heart rate. Each parameter is scored, providing a composite assessment of fetal oxygenation and overall health.
Understanding the Technology
The images produced during an ultrasound are generated by a transducer placed on the skin, which emits sound waves and captures the returning echoes. The most common form used for diagnostic purposes is the two-dimensional (2D) ultrasound, which creates flat, grayscale cross-sectional images of the fetus. This standard modality provides the necessary measurements and detailed internal views required for clinical assessment.
More advanced techniques are sometimes utilized, such as three-dimensional (3D) and four-dimensional (4D) imaging. The 3D ultrasound constructs a static, volume-rendered image, allowing for a clearer visualization of the fetal surface features. The 4D ultrasound captures these 3D images in real-time, providing a video-like display of fetal activity.
Another specialized method is the Doppler ultrasound, which measures blood flow within the umbilical cord, the fetal brain, and other vessels. This technique is valuable in high-risk pregnancies to assess placental function and ensure the fetus is receiving adequate nutrients and oxygen.