3D Ultrasound vs 4D | What is a Sonogram?

You get to see your baby for the first time live with a sonogram, and even find out the answer to “what gender is my baby?”, but haven’t you wondered what are they actually looking for? You’ll finally be able to answer the question of what type of ultrasound 2D, 3D, or 4D you want at every stage of your pregnancy.

Crash Course on Sonography: 3D Ultrasounds & 4D Ultrasounds

You will learn answers to the following questions: what is a sonogram, how does a sonogram work, how is it used to find out if the baby is healthy, am I having a boy or girl, and what’s the difference between a 3D and 4D ultrasound. Plus, you’ll learn why most women only get 2 ultrasounds their entire pregnancy!

When can I first see my baby?

You’ll be able to see your little one about 1.5 months or 6 weeks after conception.

When do I know if I’m having a boy or a girl?

The sex of the baby is often determined at the 20 week ultrasound.

So, what is an ultrasound?  Is it the same as a sonogram?

An ultrasound exam uses high-frequency sound waves to scan a woman's abdomen and pelvic cavity. This is the process of sonography. "Son-" refers to sound waves and "-graphy" refers to the process of viewing. Hence, sonography is the process of viewing with the help of sound waves. The product of the viewing process is an ultrasound. Ultrasounds are often used when diagnosing abdominal or pelvic pain abnormalities. If a patient has pain, bruising, swelling, abdominal distension and/or abdominal rigidity, the doctor might use an ultrasound to find out why. On the other hand, a sonogram creates a picture of the baby and placenta (so that’s why you see pregnant women showing pictures of the baby) but it uses the same high-frequency sound waves.  The difference is when a woman is pregnant the sonographer is looking at the baby and not the mother’s abdomen, so it is called a sonogram. Although the terms ultrasound and sonogram are technically different, they are used interchangeably and reference the same exam during pregnancy.

What are the advantages of an ultrasound?

• Real-time visualization of the fetus or organs.
• It’s non-invasive, meaning it is performed over the skin so nothing has to go into your body and its painless.
• Doesn’t use ionizing radiation, which has been associated with toxic effects on the embryo.
• Interactive, enabling the sonographer to capture different viewing planes by moving the probe.

What is a 2D ultrasound?

2D, or 2-dimensional means it sends and receives ultrasound waves in just one plane. Think of a piece of paper.  It is slicing the image one way. The reflected waves then provide a flat, black-and-white image of the fetus through that plane. Moving the transducer enables numerous planes of viewing, and when the right plane is achieved, as judged by the image on the monitor, a still film can be developed from the recording. Most of the detailed evaluation of fetal anatomy and morphology is done using 2D ultrasound.

What is a 3D ultrasound?

Further development of ultrasound technology led to the acquisition of volume data, achieved when slightly differing 2D images caused by reflected waves which are at slightly different angles to each other were combined. These are then interpreted by high-speed computing software which turns it into a 3-dimensional image. The technology behind 3D ultrasound involves 3 processes to create the picture: image volume data acquisition, volume data analysis, and finally volume display. This data is acquired through freehand movements of the probe, mechanical sensors built into the probe head and matrix array sensors which uses one single sweep to acquire a lot of data. Now you don’t have to understand the entire process before you get your first sonogram, but it is interesting to have a general idea before you see it in person.

What is a 4D ultrasound?

3D imaging allows fetal structures and internal anatomy to be visualized as static 3D images. However, 4D ultrasound allows us to add a live streaming video of the images, showing the motion of the fetal heart wall or valves, or blood flow in various vessels. It is thus 3D ultrasound in live motion. A 3D ultrasound is a picture while the 4D ultrasound is a movie.

How does a sonogram determine if the baby is healthy?

Once the 2D images are combined to form the 3D image, the sonographer can get to work. The sonographer visualizes the structures in terms of their morphology, size, and relationship with each other based on standards of what is and is not normal. For example, while visualizing the fetal heart, the operator is able to look at any of the classical fetal heart views by moving the reference dot, be it four-chamber, three-vessel, LVOT (left ventricular outflow tract AKA five chamber) or any other plane of interest. You can check out the picture below for more information on these views and you can check this website. These views can be displayed using gray-scale, color Doppler or power Doppler. The Doppler settings help to display the movement of blood through the various chambers and valves. The 3D ultrasound may help to identify structural congenital anomalies of the fetus during the scheduled 18-20 week scan.

When can I get an ultrasound?

Ultrasound exams can be performed at any point during pregnancy, but they aren’t always considered a routine part of the prenatal test. Most OBGYNs suggest moms-to-be have at least two during their pregnancy.

The first test usually occurs during your first trimester as part of a biophysical profile (a prenatal ultrasound evaluation). Your first ultrasound, also known as a sonogram, will take place when you're around 6 to 8 weeks pregnant. When you schedule your appointment, be sure to ask whether you need a full bladder for the test. Sound waves travel better through a liquid, so a full bladder can enhance the quality of your ultrasound. As your uterus and the fetus grow (and you have more amniotic fluid), a full bladder matters less.  But if you are a teacher, nurse, or doctor that is used to holding their bladder like a camel in the desert, I would recommend not going in with YOUR full bladder. These professionals have a bladder twice the size of most because we never get to pee!

What will my first ultrasound be like?

At 6 to 8 weeks your baby is very small and your uterus and fallopian tubes are closer to your birth canal than to your abdomen, so your OB/GYN will conduct the test transvaginally to get a clearer picture. The test is painless. Your OB/GYN will place a thin, wand-like transducer probe, which transmits high-frequency sound waves through your uterus, in your vagina. The sound waves bounce off the fetus and send signals back to a machine that converts these reflections into a black and white image of your baby. It will be hard to see much in this first snapshot, but a clearer photo will come around 13 weeks, which is the ideal time to share your exciting news. Your OBGYN also listens for your baby's heartbeat and estimates his age by measuring his length from head to bottom.  The doctor will usually take organ length estimates, as a control or reference point, for future evaluations. Your baby is tiny in the first trimester and grows about a millimeter a day. From this test, your doctor will be able to determine a more accurate due date and track milestones during your pregnancy. Your doctor will also be able to tell if you're pregnant with twins or multiples.  Your OBGYN will also rule out a tubal (ectopic) pregnancy, which is when the fetus grows in the fallopian tube instead of the uterus. Don't worry, this occurs only 1 percent of the time.  If you are interested in learning more about the risk factors that cause ectopic pregnancies or to have a better idea of what an ectopic pregnancy is, just listen to or read Pregnancy Pukeology Episode 23 Ectopic Pregnancy Complication.

What is a nuchal translucency test (NT test)?

All pregnant women are offered a nuchal translucency (NT) test, performed between 11 and 13 weeks, and this involves another ultrasound. The NT evaluates your risk of having a baby with Down Syndrome (trisomy 21), Edward’s Syndrome (trisomy 18), or certain heart defects. Trisomy means these children have an extra chromosome copy on the number stated next to it three because “tri” means three. In this two-part exam, a blood test measures levels of certain hormones and proteins in your body, and an ultrasound determines the thickness at the back of baby's neck (increased thickness, caused by excess fluid, indicates that he/she may be at risk for birth defects such as Down Syndrome and/or Edward’s Syndrome).

What is an amniocentesis? Do I need an amniocentesis?

In this procedure, a needle is inserted through your belly and into your uterus to take a sample of amniotic fluid, and your health care provider may use ultrasound to guide the placement of the needle. There's a very small (.5 percent) risk of miscarriage. Women whose screening test revealed a potential problem, who are 35 or older, or who have a family history of certain birth defects should consider an amniocentesis. If one of the previous criteria apply to you or your doctor feels that you need one, you may have an amniocentesis to check for Down syndrome between 14 and 20 weeks.

When will I have another ultrasound?

The second ultrasound is typically scheduled between 18 and 20 weeks to find out the gender of the baby, look for signs of problems with the baby's organs and body systems, and confirm proper growth. This ultrasound, called an anatomy scan, lasts 20 to 45 minutes if you're having one baby, but it is longer if you're having multiples. Your OBGYN uses it to assess the baby's growth and make sure all their organs are developing properly. You'll be able to see your baby's developing body in great detail, but it can be hard for an untrained eye to distinguish the kidneys from the stomach.

The doctor will check your baby's heart rate and look for abnormalities in her brain, heart, kidneys, and liver. They will count your baby's fingers and toes, check for birth defects, examine the placenta, and measure the amniotic fluid level. The sonographer will probably be able to determine your baby’s sex.  An experienced tech gets it right more than 95 percent of the time. If you don't want to know your baby's sex, let them know ahead of time. You might even get a 3-D view, which will offer a true-to-life glimpse of your baby's nose and bone structure.

So, most women only get ultrasounds in the first & second trimester. Would I get a third-trimester ultrasound?

If you've gone past your due date, your doctor may want to keep a close eye on your baby with fetal heart-rate monitoring and ultrasounds to assess the amniotic fluid levels. Other reasons for third-trimester ultrasounds include concerns about the health of the placenta, whether the baby is turned incorrectly (called breeched), and questions about whether your baby's growth is on track.

Many moms-to-be don't need an ultrasound in the third trimester, but if you're over age 35 or your doctor wants to closely monitor your baby's growth, you may get one or more before the baby is born. Other reasons for third-trimester ultrasounds include bleeding, pre-term contractions, or to attempt an inversion at 37 weeks to flip the breech baby around. You'll also get a follow-up scan if your cervix was covered by the placenta at your 20-week scan. This is called placenta previa. In 95 percent of cases, the placenta naturally moves away from your cervix by your due date. If you do have placenta previa your OBGYN may recommend a cesarean section (C-section) delivery.

Are there any risks to ultrasounds?

Side-effects of ultrasound are of low risk and provide limited exposure to the baby. Ultrasound at diagnostic levels has the potential to cause cavitation or small pockets of gas in the tissues. It also produces slight heating of tissue. While no significant health consequences have been traced over 20 years of ultrasound use, the use of unregulated ultrasound for other than medical indications is not encouraged. However, recording videos of the fetal movements is permissible if it occurs during the medically indicated examination performed by trained medical personnel, and without the need for additional fetal exposure to ultrasound energy.

Now you know all about ultrasounds and what to expect on your first ultrasound appointment and your 20 week ultrasound. From your transvaginal ultrasound to labor, NoMo Nausea is here to help make your pregnancy a bit more comfortable. If you want to listen to this podcast and hear some funny Pregnancy stories click on the link below to listen to Dr. Darna explain sonography and the difference between a 3D ultrasound and a 4D ultrasound.