Posted on April 27th, 2017 by

General Ultrasound Facts


Patients have asked me these questions on a regular basis for years. Let’s get some ultrasound facts straight, shall we? I hope it’s helpful!

What’s the difference between ultrasound and sonogram?

Technically speaking, ultrasound is the study of the subject (the field of ultrasound) and a sonogram refers to the examination itself. Although we’re really not picky about what you call it.


Is ultrasound safe?

Biohazard testing over the past forty years reveals no ill effects of ultrasound on the fetus, mother, or sonographer. However, increasing levels of heat after scanning for several hours in one area can cause cavitation or the creation of bubbles. This is much longer than the time required for performing a diagnostic test. Since no one can predict the long-term effects, only the prudent and diagnostic use of the technology is recommended by ACOG, AIUM, and ACR. The benefits of the information from diagnostic exams for patient and physician currently outweigh any known risk.


Is Ultrasound radiation?

Ultrasound technology uses sound waves, NOT radio waves. I dedicate an entire post to just that subject in the link above. No radiation is emitted by ultrasound equipment or Dopplers utilized by your physician to detect Baby’s heartbeat. X-Ray emits radiation which is why, for example, your pregnant belly would be covered with a protective shield at your dentist’s office for X-Rays on your teeth.


Can my baby hear ultrasound? 

Nope, Baby cannot hear the sound waves:) Ultrasound is just that…sound waves that operate at a frequency far beyond human hearing. Human hearing ranges from 20Hz to 20,000Hz. Diagnostic ultrasound operates in the millions of Hertz. Ultrasound probes range from about 2 – 13MHz.

True story ~ I became a little distressed once when a patient asked me if ultrasound sounded like a jet to a fetus. She had just read this in a pregnancy magazine in our waiting room! I reassured her this was inaccurate. This experience marked one of the many reasons I wanted to start my blog–to get reliable info to new moms like you!


What’s the difference between 2D, 3D, and 4D?

Almost everyone has seen the gray clouds of 2D ultrasound at one time or another. 2D allows us to see through organs and inside your baby.

Most people are familiar with 3D imaging as a fun way to see the outside of their baby. Additionally, the best and cutest 3D images are obtained later in the 2nd Trimester or early in the 3rd. Baby’s skin has developed more fat at this point which makes for chubbier cheeks! Occasionally, a high-risk practice (MFM or Maternal Fetal Medicine) will usually also use 3D to assist in visualizing a fetal abnormality. We also frequently use the technology for GYN scans to attempt a better look at uterine shape and/or IUD placement.

4D can be described as 3D in motion or a live 3D image. So, where 3D is a still image, a 3D video of Baby moving is actually 4D.


ultrasound facts, 3D, 9 Weeks pregnant

3D 9-Week Embryo

Ultrasound Credentials for Sonographers


What’s your title? Are you a nurse or in X-Ray?

We’re not nurses, though some of us do cross over from RT (X-Ray) or other areas of Radiology. Sonographer, Ultrasonographer, or Ultrasound Technologist are a few of our titles. We are specifically and formally educated in the field of Ultrasound.

RDMS stands for Registered Diagnostic Medical Sonographer. A sonographer earns these credentials through ARDMS when he or she has passed a registry examination in Ultrasound Physics as well as his/her ultrasound specialty. A certified sonographer typically has at least two years of experience under his/her belt.

DMS refers to someone who has completed some sort of formal or on-the-job ultrasound training but has not yet taken/passed the registry examination.


What do you think of those 3D places?

Having posted on this often, I understand a patient’s desire to go, but I’m not a fan. Not everyone who scans an expectant mom in a 3D non-medical business is a certified OB sonographer. Some have no formal ultrasound training whatsoever! I know you may be surprised by this little-known fact, and so was I.

These businesses are not regulated like medical practices. They may not be knowledgeable of or follow guidelines for equipment maintenance. Ultrasound equipment that is not properly maintained can be an electrical hazard for mother and/or fetus! Do your research and at least ensure your sonographer possesses RDMS or, at least, DMS credentials. Please read the post in the link above!


Performing Your Exam


When can I expect to have sonograms in my pregnancy?

Every practice is different. Most physician’s order a first-trimester ultrasound examination to date the pregnancy. This is usually performed with a transvaginal probe. If no other problems necessitate another scan, you’ll receive your next exam around 18-20 Weeks. Most women know this scan as the anatomy screen where we evaluate fetal and maternal parts for abnormalities.

*Your doc does not order this exam to determine fetal sex!* However, most sonographers will happily provide the info if at all possible (as long as policy allows)! Also, important to note here is that determining sex is never a guarantee nor should it be an expectation. Sometimes, those Little Sweet Peas just won’t cooperate! You can read more here about those limitations. Note of advice for moms: Don’t pre-plan your Gender Reveal party for the same day as your ultrasound! The health of your pregnancy determines whether you will receive more ultrasound scans later in your pregnancy.


Can you predict how much my baby will weigh at birth?

While we can measure your baby’s head, belly, and femur for an educated (called EFW or Estimated Fetal Weight) guess for weight at the time of your scan, a large discrepancy for weight determination exists due to fetal position and sonographer skill. We can typically track a trend for large or small babies. We know the average gained weight in the last few weeks is about 1/2 lb per week. However, every baby is different!


Ultrasound Facts About Fetal Sex


Most expectant moms today already know this little fact. The ultrasound machine is never “wrong” in determining fetal sex. Actually, it is the observer who is incorrect!

Guessing the wrong sex can be due to one or a combination of many factors. It is possible your baby was in a difficult position to see well. Maybe you were too early in your pregnancy for an accurate guess. In addition, an overall poor view can also limit fetal sex determination!


Facts About Your Results


Yes, the sonographer can read your examination. However, your OB/GYN physician or radiologist must ultimately interpret the images and report we create. Consequently, only your physician can legally give you results! Read more about why here.

However, most of us are more than happy to educate you about what you see on the monitor (minus a diagnosis!). I loved sharing how we measure and pointing out all your Baby’s parts for any inquisitive parents or family.


Feel free to email me at with your comments or questions!

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Posted on January 23rd, 2015 by

One thing Moms wonder about most while waiting for the big day is how much Baby she is actually going to have to push outta there!  If it’s not your quasi-friends telling you you’re huge or a perfect random stranger asking if there are two in tow, then it’s your bathroom scale not-so-gently reminding you of your ever-changing shape. You see the numbers creepin’ up like your too-tight fave pair o’ jeans. If you’re really lucky, you just failed your two-hour glucose. Just when you thought pregnancy was going to be your temporary ticket to Oreotown, your doc is telling you to find a new love for wheatgrass shakes and to hang it up on the Beautiful Bavarian you have a date with for breakfast every day…your husband should be jealous the way you eye those things. I know, I know. I could eat half a dozen of them myself and I can’t use the excuse of growing a human or “Baby wants it; he told me”. Of course, you could use the disclaimer my old Italian mother swears by..if you crave something and you don’t let yourself have it, your baby will be born with a birthmark in the shape of that food somewhere on its body. I kid you not; she really believes it. All I can say is it’s a good thing it’s only an old wives’ tale or there would be an awful lot of gestational diabetes babies out there born looking like pizza and french fries.  Hmm, I wonder what an ice cream birthmark would look like? A dripping cone? The whole carton?

I guess one of the favorite pastimes of Moms today in this age of quickly-changing technology is consulting the highly-revered but often-times inconsistent daily app. You want to know if your weight gain is normal, if it’s too high or too low. Was quasi-friend right to tell you not to have that second piece of cake? Personally, she’d be no friend of mine after that. Let them eat cake! Or it’s “Aw, my baby is an eggplant today.”

So, knowing we have this insatiable appetite (no pun intended) for knowing everything everyday or at least being able to look it up and get some sort of answer, is it any wonder we wonder at all about the weight of our babies, too? This is where one role of ultrasound is important. Even though very subjective (as ALL ultrasound is), knowing how to take good measurements of your baby provides your doctor with some really important information about fetal well-being.  Read on from One Confused Momma who was originally confused about gender then more confused about Baby’s size!

ocm:  Okay so new question!! How accurate are ultrasound measurements as far as baby’s weight?? I had my last one today and she measured him at about 4lbs and I’m only 29 weeks and 3 days.

wwavb:  Hi, again! It varies and it’s not an exact science. Generally speaking, the measurements we take of the head, belly and femur are subjective but have a standard deviation of 3wks in the 3rd trimester. The total weight estimation will probably be somewhere around +/- a half pound or so at this gestational age. If we get a measurement that is a couple of weeks ahead, it can still be very much within normal limits for size. We also see that babies can grow in spurts so if the belly measures big now, it doesn’t mean it will nearer your due date. We can also determine through serial scans if a baby is trending large or small and your physician will follow fetal growth accordingly. So! All that being said, if your doctor feels baby will be big, he or she will likely keep an eye on size. This is a good question for your doc at your next visit!


I don’t have one with me now but I’ll print a report of a 3rd trimester biometry (fetal measurements) with an EFW, or estimated fetal weight, and share it with you next week, if not tomorrow!

I’ll also add here that your doctor uses the fundal height or the measurement in centimeters to the top of your uterus he/she obtains when you go in for visits to determine growth in generalities. If your uterus measures really large, your doc may order a sonogram to see if Baby is big or if you have too much fluid, polyhydramnios. We see a lot of this, by the way, and don’t always have an explanation for why it’s there. Conversely, if you measure pretty small, your doc may want to find out if Baby is not growing appropriately and to ensure you have enough fluid. Mom’s body type can also influence how your belly looks, too! You can spend all day downloading apps but, as always, questions pertaining to you and your pregnancy and baby specifically can only be answered by your doctor! (And not Dr. Google)

At the end of the day, our shapes during pregnancy are as different as we all are different from one another. We have to quit comparing our bellies to those highly polished on the cover of Vanity Fair and even one another and know we are doing what is right as long as we are adhering to our doctor’s guidelines! Sometimes it’s out of our control and our babies end up too big or not thriving well. Either way, that’s why you have people like me around!

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Posted on May 22nd, 2014 by

EFW or Estimated Fetal Weight

Here’s an email I received from a UK reader asking about determining Baby’s estimated fetal weight or EFW. Read on for my response!

reader:  Hi, I was just wondering how accurate scans are at estimating weight? I’m 36 weeks +1, and I had a growth and reassurance ultrasound today. Baby was perfect :), and they estimated 7 lbs. This is my 4th child, and the only full-term baby I’ve had was my last. He was 7 lb 10 ozs. I am a little worried this baby is going to be a 9-pounder and that I’m going to have a difficult labour. This is my last baby, so I really don’t want to spend these last weeks worrying over nothing. Any info would be gratefully appreciated. Thanks in advance. I love reading your blog!

wwavb:  I love my UK readers! First, let me say I am happy you found my blog and are enjoying it. Thank you so much for saying so! I hope you’ll spread the word!

Now on to your question. I’m unsure what the discrepancy is in the UK for fetal weight. Our machines may be calibrated slightly differently here in the states. That said, 1 lb +/-  is not unheard of and sometimes can be greater depending on the level of skill of your sonographer and fetal position. These factors can make measuring baby more difficult and less accurate, which is precisely why it’s called “estimated.”

If your baby is at 50% or thereabouts, it means he is average in size and will gain, on average, about
1/2 lb/wk until delivery. If your baby is measuring bigger then average (which I wouldn’t know without seeing the individual % for each measurement), it’s feasible Chunky Monkey could gain a little more each week.

Just know that if this baby ends up being larger doesn’t mean you’ll have problems delivering!



It’s also important to note that if your baby is measuring smaller than average, his or her weight gain will likely equal less than that 1/2 lb/wk estimate. Everyone wants to mentally prepare for what they are going to have to push out which is totally understandable!

Best wishes for a quick and easy labor and delivery! for your questions and pics:)


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Posted on March 31st, 2014 by

I commonly get questions about the report as I pull up this page on the monitor when I am revealing Baby’s weight after taking a biometry (that is, the measurements of Baby’s head, belly and femur).  Patients usually want to know why the measurements I took differ from the current gestational age.  The fact is they can..this is not an exact science so even a difference of a week can be totally normal.  Sometimes, a large difference can simply reflect a dating issue, meaning you are either farther or less along than you thought.  Your doctor knows how to differentiate between the two.

Check out part of the report below.  This is an old exam on a Baby B who was growing just fine!


First, notice GA.  This is the Gestational Age of Mom currently.  EDD of 8/15/2007 is the Estimated Due Date determined earlier in the pregnancy which corresponds with the GA.

Below that, you’ll see AUA or Actual Ultrasound Age.    It says 19w3d, a couple of days farther along.  This is merely an average of all four measurements taken and is considered consistent with GA, meaning her due date will stay the same.

The biometry consists of the BPD (width of the fetal head), HC (head circumference), AC (abdominal circumference) and FL (femur length).  The names in parentheses refer to the physicians whose charts for these measurements are programmed into the software.  The values are taken in centimeters and each one represents a GA based on that measurement.  You can see that the BPD measured 8d larger.  This is totally normal.  All the other measurements were pretty close to GA within a couple of days.  Again, these all demonstrate normal growth.

Below the dimensions you’ll see EFW or Estimated Fetal Weight calculated in grams with a small standard deviation and also displayed in ounces.  This is determined by the four above measurements entered into the system by the sonographer.

Below that are ratios of these measurements.  If baby isn’t growing properly, it will reflect here but we will also see that in the individual measurements.

Below that is an M-Mode or Motion Mode which demonstrates the fetal heart rate (HR) taken.  120 – 160bpm or beats/minute is totally normal.

This is only a small portion of a report on twins but enough to explain Biometry.  This concludes Ultrasound 101.

Have a great day, people!

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Posted on March 15th, 2014 by

Or, rather, Estimated Fetal Weight. This is the approximate weight of the fetus after we measure the head, abdominal circumference and femur.  Our machine takes this information and plugs it into the software to estimate Baby’s weight.  I’ve posted on BPD, HC, AC and FL before so I won’t focus on HOW we get those measurements today, but instead, the accuracy of them.

I am asked several times per week, “Now how accurate is this weight?”  Are we always right on with birthweight?  No.  Are we always close?  Another no.  But MOST of the time, we are.  It is an educated guess and based only on the measurements WE take and there are many variables that play into obtaining those properly.  As baby gets closer to the EDD (Estimated Date of Confinement), Baby gets bigger, the head becomes more engaged, and the fluid can start to diminish a bit. There is only one right way to measure Baby and all of these things make her harder to see and these measurements more difficult to obtain, especially depending on Baby’s position.

Also, Baby is packing it on in the last month!  Average growth is about 1/2lb per week!  If you’re baby is trending heavier, Baby will usually gain more than the 1/2lb and if trending smaller, then less than 1/2lb per wk.  This is why when a patient comes in at 32wks and asks how much I think her baby will weigh at birth, I always say “If I could predict that, I could have retired a long time ago!” Sometimes babies grow in spurts, too.  We might see a huge head at 30wks and a few weeks later see that everything else caught up.  So, NO WAY to predict!

Technically, our software tells us at term to figure plus or minus 1.5lbs. However, IF I feel that I am getting really easy and accurate views of the head and belly (especially the belly since most of the EFW comes from the AC or abdominal circumference), then I feel pretty good to say that I may be over-estimating by about a 1/2lb.

Remember, if you get an ultrasound and an EFW at week 38 and you deliver at 39, don’t forget to add in that extra poundage!

Here’s to a fat and happy fetus!

And if you have stories you’d like to share or questions about weight, feel free to email me or comment on this post!

Thanks for reading,

wwavblogger 🙂

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