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While each pregnant person’s situation is unique, there are some commonalities to the use of ultrasounds as the pregnancy progresses. When used in medicine, the technology uses sound waves to develop pictures of the fetus during pregnancy, to determine size, identify anatomical features of the fetus, and sometimes measure blood flow and amniotic fluid levels, among other uses. This guide will provide a general overview of the different categories and types of ultrasounds.
While this guide provides helpful information about prenatal scans, your doctor will officially interpret your results during a follow-up appointment or phone call. If you’d like early access to your results, PocketHealth offers secure, instant access to your report when it is available. This allows you to review the findings in advance and prepare any questions for your follow-up.
Ultrasounds are used for a variety of purposes, not just prenatal care. However, the method is generally the same. High-frequency sound waves are produced by a wand-like device called a transducer. As the technician moves the hand held transducer across the area being scanned, these sound waves bounce off organs and other internal structures, echoing back to create images that are captured and saved for later analysis. In prenatal ultrasounds, these echoes reveal the embryo or fetus, allowing for the evaluation of development, growth and other health functions.
Typically, healthy pregnant patients receive two ultrasound exams: one during the first trimester and one during the second. Early pregnancy ultrasounds are used to determine viability, gestational age and embryo implantation. If an embryo implants outside of the uterus, it is considered an ectopic pregnancy. The second trimester scan is to evaluate fetal anatomy and development factors.
Additional scans may also be performed when the clinician feels they are necessary, and a third, optional type of ultrasound is commonly performed between weeks 11 and 13 in order to screen for chromosomal conditions. This is called a nuchal translucency screening and will be detailed later in this guide.
As for general categories of prenatal scans, the American Congress of Obstetrics and Gynecologists (ACOG) categorizes ultrasounds during pregnancy as standard, limited and specialized.
The standard fetal ultrasound checks fetal physical development, with the clinician looking for major developmental issues, while also estimating the fetus’s gestational age. During the first trimester, the ultrasound is the most accurate way to confirm the age, by measuring the fetus’s crown-to-rump length. The predictions are generally accurate to within five days of the expected due date. The second scan is usually performed between 18-22 weeks, and is used to:
A limited fetal ultrasound is performed to help the clinician answer a question, like confirming the fetal heartbeat or checking fetal positioning. An optional nuchal translucency (NT) ultrasound would be done around 10-13 weeks, to measure the fluid-filled space behind the fetus’s neck. An abnormal measurement could indicate chromosomal issues like Down syndrome, and the clinician may also order a blood test to measure hormones and proteins. A clinician may recommend limited ultrasounds for other medical concerns, such as hypertension, maternal diabetes, bleeding, low amniotic fluid or advanced maternal age.
Specialized fetal ultrasound examinations may be recommended if the clinician wants to monitor something like fetal growth. This exam may use a special ultrasound technique like 3-D ultrasound or Doppler ultrasound, which will be further detailed in an upcoming section.
While ultrasounds in general involve using sound waves to create a picture of what is inside the body, there are different techniques.
A transabdominal ultrasound is the traditional version those who are pregnant may envision. The patient lies on their back and the technician moves a transducer over the abdomen after applying a thick gel. This technique works best when the patient drinks water before the exam, as a full bladder makes the sound waves travel better. After around 24 weeks of gestation, many patients no longer need a full bladder for ultrasounds, as the baby is large enough to be seen clearly on the scan without it.
While the sound waves work the same way, the transducer is a wand inserted into the vagina. The patient does not need a full bladder for this exam—an empty or partially full bladder is fine. For prenatal scans, transvaginal ultrasounds are typically only needed during the first trimester, though exceptions may apply depending on the patient.
While a standard ultrasound shows pictures, a Doppler shows blood flow. Doppler ultrasound is used to hear the fetal heartbeat and see how well the blood is circulating through the vessels or umbilical cord. It may be used for patients who have complications like diabetes, high blood pressure, heart or kidney problems, placental development issues or potential fetal growth issues. It’s more typically done during the third trimester.
Ultrasounds may be used to guide procedures, like chorionic villus sampling (CVS) and amniocentesis, when a needle is inserted into the womb to biopsy the placental tissue or the amniotic fluid. These tests look for abnormalities. The ultrasound ensures that the needle is in the right location.
This more advanced ultrasound takes thousands of pictures at a time, producing a photo-quality image. It may be used to monitor the baby’s organ development, and to look for potential facial abnormalities. It can also be used to visualize problems with the uterus.
4-D ultrasound is similar to 3-D ultrasound but it is a video. It shows the baby’s movement. It may also show potential fetal abnormalities. Both 3-D and 4-D ultrasounds are sometimes referred to as “keepsake ultrasounds,” as they provide more realistic views of the baby and people like to frame or share the images. Medical associations and government health organizations do not recommend getting these ultrasounds unless there is a medical necessity.
While the ultrasound technician can answer questions about the scanning process, they cannot provide diagnoses or explanations. A radiologist will interpret your report, along with your obstetrician, who may offer additional insights. These results will usually be communicated to you at a follow up appointment.
If you’d like to view your report before your appointment, PocketHealth provides faster access, allowing you to see the results as soon as they are officially uploaded. This gives you time to review the findings and prepare for your next medical visit.
Although your doctor will provide an official explanation of your results, accessing your report before your appointment can give you an early glimpse. It’s common to find the medical terminology complex and confusing, but Report Reader makes it easier by offering clear, straightforward definitions for medical terms—simply tap or click on any underlined words to reveal their meaning.
Here are some common questions regarding prenatal ultrasounds.
Your obstetrician or the imaging facility should give you instructions, but here are some helpful tips for ultrasound preparation:
Prenatal scans are considered safe and effective. However, some patients may have allergies to latex or other medical substances, such as the gel used during the procedure. It’s helpful to communicate any known allergies in advance so that accommodations can be made. Additionally, some patients may experience mild discomfort during a transvaginal ultrasound. If this happens, it may be a good idea to inform the technician so they can make adjustments to improve comfort.
Pregnancy can typically be detected by ultrasound as early as six weeks gestation. However, it’s not uncommon for patients to have a scan at this early stage and find no visible activity. If conception dates are incorrect, it may be too early for the pregnancy to be detected, meaning the gestation is actually earlier than expected. In such cases, repeat imaging is often scheduled in one to two weeks to try again.
Fetal anatomy takes time to fully develop. One of the first indicators of sex anatomy is the genital tubercle, often referred to as the “nub.” The angle of this tubercle is thought to be a predictor of the baby’s sex. If the nub is less than 10 degrees from the spine, the “nub theory” suggests a female fetus. If the tubercle is over 30 degrees from the fetal spine, it is more likely to indicate a male.
The accuracy of this theory is about 70 percent at 11 weeks gestation, meaning an ultrasound performed around this time may give an indication of sex. By 13 weeks, the accuracy increases to nearly 100 percent. However, this requires clear images or specific fetal positioning for an accurate evaluation, which is not always possible. The standard ultrasound for determining fetal sex is the 18 to 20 week anatomy scan, as by this time the baby is large enough for clearer visualization.
PocketHealth makes it simple to keep track of your prenatal reports and ultrasounds. All of your vital imaging is in one secure location and can be accessed online anytime or even shared with family and friends. If needed, reports can also be easily shared with other physicians in your care team. When used in conjunction with your medical provider’s professional advice, it is a powerful tool for organizing and understanding your imaging results and pregnancy health. With such easy access to all of your ultrasounds, you can also print them from home or even share them with friends and family.
Another tool for your health is MyCare Navigator, which provides personalized insights to your health and identifies any recommended follow-up steps. This feature can also generate individualized questions to ask your doctor based on the findings in your report, ensuring you make the most of your consultation.
