Hello fabulous ladies! I will be the moderator for this DB. I can't believe it is already the last week of the quarter and we have learned so much. Great job on the discussion boards so far - let's keep it up!

When posting your responses, some things to keep in mind are:

- What is the purpose of the third trimester exam and how does it differ from the other OB exams? 

- What key factors are you looking for when assessing the fetus at this time?

- If something is wrong, how are you going to paint the picture to best communicate with the radiologist and prove what your are seeing? 

- What else should you document to help the radiologist and perinatologist determine what the next steps are in terms of managing the health of the mom and fetus? 

As always, we love to see helpful images and videos and share any experiences you have had at clinicals. I'm looking forward to learning from you all!

If I find that the fetus is measuring smaller than their gestational age I would refer back to their previous exams. It's important to notate if this is a new finding or has the fetus measured small consistently. It important to understand what parameters may also be influenced by genetics. We know that if mom and dad are shorter that may yield a shorter child, and the same is true of tall parents.

If the fetus had not measured small previously it's important to double or even triple check our measurements. If we are not in the correct plane for our measurements it can yield a false reading. If the measurements match every time we know something is truly askew.

When the fetus measures small early in the pregnancy we become suspicious of symmetrical IUGR. if changes aren't noticed until the second or even third trimester we worry about asymmetrical IUGR. In the event of an asymmetrical IUGR we should notice a disproportionate size at the fetal head and abdomen which is due to head sparing.

During the third trimester our focus shifts from surveying full fetal anatomy to completing a more targeted exam. Although we are still looking carefully at baby our main areas of interest should include biometry, AFV, biophysical profile, and babys presentation! We figure at this point in the pregnancy most anomalies should’ve already been documented and followed up on, but we must still be diligent in surveying through the entire fetus!

Heres 2 graphics I really like about the biophysical profile:

If I am doing a 3rd trimester scan and the fetus is measuring smaller than it should be, my next plan of action would be to take one more set of measurements to verify that the smaller estimation is not due to imprecise calipers or scan planes. Once verified, I would also look at AFV and monitor for sonographic components of the Biophysical Profile. AFV is done by measuring an empty space sample in 4 quadrants of the uterus (using the umbilicus as center). One of the techs at my site showed me how to use dual screen to actually show 4 different views in one image, which I thought was pretty ideal for concisely illustrating AFV to the radiologist. These “empty spaces” should be measured perpendicular to the table (not maternal belly) and should be free of fetal anatomy and umbilical cord.

I would also consider a doppler of the umbilical cord and MCA. We could also look at the Ductus Venosus doppler but that is I think more for perinatology as Dr. Wilson mentioned in lecture.

When we see that the fetus is measuring smaller, we being to suspect IUGR. It is important to start questioning what might be causing this smaller EFW. I really liked this image (below) that highlighted some different factors that can be associated with IUGR.

Since we are scanning in the 3rd trimester, what is important now is can baby thrive in utero, or will it have higher success with an early delivery. The doctors are the ones who make that decision, but they use our sonographic findings to inform those choices, so it is important that we document everything relevant to fetal in utero prognosis.

Hello All,

I think if the fetus was measuring smaller than it should be I would be worried about if he/she is thriving. I would be interested in seeing if they are still developing or barely making any progress. First, if I noticed that the fetus was smaller than normal I would probably start with amniotic fluid measurements. Next, I would go into doppler. I would first want to see if the umbilical arteries had a strong uptick in systole and a low resistant diastole. If this was abnormal I would then go to the Middle cerebral artery to see if the S/D ratio was > 3.0. If lower than 3.0 a waveform with low resistance in diastole may suggest cranial sparring and could be a reason why the fetus is measuring smaller. Next, I would look at the Ductus venosus waveform to see if forward low resistant triphasic flow was present. I would interrogate all of these vessels to see if the fetus is thriving but may be on the smaller side or if they are smaller because their environment has stunted their development. If all of these were normal I would suggest a follow up appointment to track the growth of the fetus. 

I think as a sonographer during the third trimester and last stage of pregnancy we really just want to make sure the fetus is still growing and in a good environment. I would say this thought process has changed from the first 2 trimesters because then it was more so the question of is there anything developmentally abnormal or do they present with anomalies. You are really interrogating every little part of the fetus to see if everything has formed accordingly. Whereas in the third trimester it is more so about will this baby die in utero or should they be taken out and given care outside of the womb. At this stage it may be important to perform biophysical profiles to see if the fetus is prospering.

 Here is a great image showing progressive loss of diastolic flow

If I noticed that a third trimester fetus was measuring smaller than it should be, I would first go back and double check my measurements. I would do an additional head circumference and abdominal measurement. Then I would compare these two to see how the HC/AC ratio is. This can help me further assess what type of IUGR the fetus may be suffering from. If the ratio is the same, then the entire fetus is smaller than normal and this signals symmetrical IUGR. If the HC/AC ratio is two standard deviations above the mean then this shows that the baby has asymmetric IUGR and the head was spared.

I would also want to assess the amniotic fluid in this pregnancy. Oligohydramnios is often associated with IUGR and can be diagnosed if the AFV is less than 5 cm.

I would additionally want to assess the fetal and maternal blood vessels and see if the fetus is getting enough blood. I would Doppler the umbilical artery and vein, the middle cerebral artery, and possibly the maternal uterine artery or ductus venosus. I would want to look for any signs of decreased diastolic flow in the umbilical artery or uterine artery, and I would want to look for increased diastolic flow in the MCA as this waveform should be biphasic. I would also want to check for any signs of reversed flow as this can show that the fetus isn't getting enough blood.

A biophysical profile assessment may also be beneficial to assess the status and well being of the fetus. This consists of evaluating their breathing, tone, movement, AFI, and cardiac function.

The third trimester is a time where we are no longer looking at the detailed anatomy and are instead assessing how the baby is thriving and if they are safe to be delivered. In this stage there is often less amniotic fluid as the baby has grown to fill most of the amniotic cavity, so detailed anatomical images are harder to achieve. The anatomical assessment is instead typically done in the second trimester so any anomalies should be well noted by now. In the third trimester we may be looking at the maternal cervix to assess if there are any issues of cervical incompetency and we may also be looking at the fetal position to see if a vaginal birth is possible. 

This helpful chart shows the different treatment routes for a baby with IUGR and when delivery should be attempted.

While scanning a baby for the third trimester, one of the most important things we're looking for is to see if baby is measuring and growing properly. If I notice or suspect that the baby is measuring small, I'm immediately going to put my detective hat on and start looking for reasons as to why the baby might be measuring small.

The first thing I would think of is IUGR, and that the baby somewhere isn't getting the proper nutrients or blood flow it needs to thrive and grow. So in that case, I would start checking amniotic fluid levels, I would also check the mother's history or ask if she has a history of hypertension. This would also be a time where I would think a biophysical profile would be necessary to properly check what's going on with this baby.

I'm going to want to check the baby's breathing movements, body movements, tone, and amniotic fluid volume, and also a non-stress test should be completed. It's very important to find out what's going on with this baby, especially since it's later on in the pregnancy, so we want to shift our minds to thinking tis could possibly be something more serious that we really need to resolve if possible. 

I added a picture below of the difference between symmetric and asymmetric IUGR.

The development of the fetal structures and organs were previously examined during the 20 week anatomy scan for anomalies. By the third trimester follow-up exam, our main concern is appropriate fetal growth and weight for the gestational age to see if the fetus is thriving. Typical biometric measurements are taken as well as the calculation for estimated fetal weight. If the fetus is measuring small for its gestational age, first I would have to see if FL, HC, AC and BPD are all measuring proportionately small (symmetric IUGR), or if there are discrepancies amongst the biometrics (asymmetric IUGR). 

Symmetric IUGR is diagnosed when the fetus is measuring proportionately small across the board and estimated fetal weight falls below the 10th percentile for the gestational age. This is due to an intrinsic developmental impairment occurring in the first or early second trimester resulting in decreased cellular proliferation of all the fetal organs. Causes include early infections, chromosomal abnormalities, and congenital malformations. Compared to asymmetric IUGR, outcomes for symmetric IUGR are usually worse. 

Asymmetric IUGR occurs in the third trimester and the AC will measure smaller than HC. The EFW is below the 10th percentile and the HC/AC ratio will be higher than normal. The HC and AC are similar in weeks 13-33 and the AC should be larger than HC after 33 weeks. Asymmetric IUGR is caused by issues with the maternal blood supply to the fetus or placental issues. 

When we see IUGR, we'll want to use spectral Doppler to assess the waveform of the umbilical artery. We can also assess the waveforms of the middle cerebral artery, umbilical vein and ductus venosus to see if they are abnormal. If the waveforms exhibit fetal compromise, the radiologist and perinatologist will want to know in case the fetus needs to be delivered early. 

Umbilical artery: Low resistance waveform and continuous forward flow and a sawtooth appearance. A normal S/D ratio is less than 3.0. Absent or reversed diastolic flow is concerning for placental insufficiency.

Middle cerebral artery: High resistance waveform and continuous forward flow. A normal S/D ratio is greater than 3.0. A S/D ratio less than 3.0 is abnormal and indicative of brain sparing due to fetal hypoxia. Brain sparing is related to the abnormal HC/AC ratio seen in asymmetric IUGR. 

Ductus venosus: Triphasic wave with continuous forward flow composed of ventricular contraction, ventricular diastole and atrial contraction (a-wave). Decreased, absent, or reversed a-wave is indicative of myocardial impairment or issues with the right venticle. 

Umbilical vein: Continuous monophasic flow toward the fetus as it is transporting oxygen and nutrient rich blood from the placenta to the fetus. Can appear phasic in response to fetal respiration or hiccups. 

Amniotic fluid should also be evaluated for oligohydramnios or polyhydramnios as we have previously discusses. Normal DVP is 2-8 cm and AFI is between 5-25 cm (or 5-20 cm). These measurements should be taken in plane perpendicular to the maternal spine. Oligohydramnios is often a sign of IUGR and chronic placental insufficiency. The placenta and maternal anatomy should also be assessed for glaring abnormalities.  

Below is a diagram showing some factors causing IUGR. Here is also a link to Radiopaedia's article on IUGR including sonographic assessment and complications.

I have helped scan a couple of follow up 3rd trimesters now, and we follow a separate protocol for limited OBs. My site starts with the long and trans cine sweeps, sag cervix and placenta picture to measure cx length and plc trace, trans DVP, heart rate, and 2 measurements each of BPD/HC, AC, and FL. I would check prior imaging to see how much smaller baby was measuring and if they are consistent in growth from exam to exam. I would make sure my measurements are accurate as possible and compare the head and abdomen measurements. If there is IUGR, the head may be larger than the abdomen (asymmetric IUGR, typically begins late 2nd/3rd tri), or it may be proportional to the abdomen but still small for dates (symmetric, typically begins 2nd tri). 

In addition, in the 3rd trimester we want to make sure the fetal lie is documented accurately. I always think of this because I start all of our OB scans, so my CI checks what I write as the lie and confirms what I see presenting to the cervix. In the survey 2nd trimesters, any fetal lie is okay since the baby moves around quite a bit and changes position often. By the 3rd trimester though, we like to see a vertex lie with the head presenting to the cervix. With normal 3rd trimester pregnancies, our thoughts have changed from the 2nd trimester "is everything there, the right size, the right appearance?" to "is this baby in the right parameters for delivery at this approximate date?" and if not, what can the doctors potentially change to assist the mother and baby in delivery, such as C-section or early or postponed delivery.

If I find that a fetus is measuring smaller than it should be I would triple check my measurements to make sure they are all accurate, I would also  go back and look at past exams and see if this is a recurrent finding. When a baby is small for gestational ago, there could be other things going on as well so checking the fetal environment would be an important next step. I would do this by completing a biophysical profile even if this isn't what was ordered. I would also add extra steps into my examination like Umbilical artery, middle cerebral artery, and ductus venous dopplers if necessary.

A consistently small baby could be a case of IUGR and doing extra work up to prove this is also something I would do by comparing HC, AC, FL, and BPD measurements. I can also determine the type of IUGR by assessing if the baby is symmetrically small or if its asymmetrical with a small abdomen and normal head size. I would also be looking for abnormalities in these waveforms like high resistance in the UA waveform when it should be low, or a reversed A wave in the ductus venosus waveform.

Some other things to think about when moving into the 3rd trimester are presentation, we want to see the baby in a cephalic position and if this isn't the case at 36 weeks when the physician can attempt a external cephalic version, which is where the baby is moved externally into the cephalic position and if this isn't successful then a C-section may be needed. 

Another thing to be aware about it the placenta location. If the mom has previa and it hasn't grown out of the way of the internal os by the 3 trimester then a vaginal birth won't be possible. Placental abruption is another factor to take into account because it's most common in the 3rd trimester. It occurs when the placenta separates from the inner wall of the uterus before birth. It can also deprive the baby of oxygen and nutrients and cause heavy bleeding in the mother. 

Our thought process has changed in the way that we now aren't so worried about the anatomy side of this baby, we are more focused on the environment and how this baby is thriving in it. What's more important now is the baby's well being. Is the fluid okay, is the baby's growth on track, how is the movement, is the baby prating breathing, things like this is what makes the 3rd trimester scan important. 

If I was scanning a third trimester follow-up and noticed the fetus is measuring smaller than it should be, I’d first double, and triple check my measurements. Doing so, I could rule out incorrect measurements due to improper scan planes. If I continue to get the same small measurements, I would be thinking of the possibility of IUGR. A diagnosis can be made when the EFW is < 10th percentile for gestational age, and we should obtain BPD, HC, AC, and FL.

We know there’s two types of IUGR that we focus on. Asymmetric IUGR is the most common type, and it occurs later in pregnancy, usually second or third trimester, and it’s distinguished by the normal head and brain size, but small abdomen, which is due to brain sparing. A HC/AC ratio should be obtained to determine if we’re dealing with asymmetric IUGR. Symmetric IUGR occurs early in pregnancy usually in the 1st trimester, and brain sparing doesn’t occur, so all indices are small: head, abdomen, long bones. 

Biophysical profile assessment should be performed to evaluate the baby’s health and ability to thrive within the womb until delivery. It documents fetal breathing, movement, tone, amniotic fluid, and non-stress test although we don’t conduct the last one. Doppler of the umbilical artery, umbilical vein, and MCA may also be useful to check.

In the third trimester, we shift our focus from the anatomy scan mentality where we take a close look at all fetal parts in great detail, to focusing on determining if the fetus is stable, thriving, and able to safely remain in the womb until delivery. We’re looking for indications that fetal growth and organ development is doing well, and that the mother is stable and continues to provide a safe environment for the baby. 

This page is a great summary of IUGR and I also really liked this chart Candee shared on her presentation! At my site I feel like I’ve only seen them use an AFI percentile chart, so I’m really glad we learned about these other parameters.

https://radiopaedia.org/articles/intrauterine-growth-restriction?lang=us

If I were doing a third trimester follow up and noticed that the fetus is measuring smaller than it should be my next plan of action would be doppler. Performing a doppler study on the umbilical veins, arteries, middle cerebral artery and ductus venosus will help us in determining or confirming if there is an issue with the fetus or if the fetus might have IUGR. Making sure that the fetuses head circumference to abdominal circumference is in the correct proportion which is supposed to be 1 to 1.  There are two types of IUGR we might expect asymmetrical and symmetrical. We would see symmetrical earlier on in the pregnancy and asymmetrical later on second or third trimester.  We would see symmetrical as the fetus as a whole getting smaller and asymmetrical with inproportionate limbs and abdominal. 

However, before every exam the Sonographer should make sure they are comparing the fetuses previous measurements to have a good idea of the growth trend. Then I will check the fetuses organs to make sure that they look normal for example the kidneys the liver and vessels.  Making sure that I'm getting multiple feutus measurements and not just using one to determine that the fetus is small.  

I know DR. Wilson stated that she performs a biophysical profile during every exam, which is what I am going to implement in my scans.  Therefore I would perform the BPP, to ensure the baby is breathing, moving, has fetal tone, and cardiac movements.

Next I would check the amniotic fluid volume making sure it is not below five and not above 25.  

https://www.youtube.com/watch?v=y4w1HqIjv0w

This is a great Youtube for the comparison of IUGR to SGA

Hi everyone,

If I am a sonographer and I noticed that the third trimester baby I was scanning was measuring smaller than normal, I would first make sure to double check all of my biometric measurements so I do not create any false abnormalities. The first thought in my head after double checking my measurements would be that the baby has some sort of IUGR and to check for that by comparing the abdominal circumference to head circumference. Symmetric growth restriction leads to reduction in all biometric measurements whereas asymmetric occurs when the abdominal size is smaller than the head circumference. I would also check amniotic fluid volumes and ask the mother if she is having any issues currently like diabetes, high blood pressure, etc. These are all clues in my investigation in finding out what could be possibly wrong with the baby. If the baby is measuring small, it is not getting all the nutrients it needs so I would doppler the umbilical vein to make sure baby is getting all the blood it needs. If I see anything abnormal with the umbilical vein then I will check the middle cerebral artery for cardiovascular distress or hypoxia. While I am checking all of this, I am also mentally noting how often the baby is moving around and flexing his/her limbs so I will check the biophysical profile (BPP) of the baby so examining baby's breathing, heart rate, muscle tone and movement. I have included an image that summarizes what is evaluated during a BPP test:

In the circumstance a fetus was measuring smaller than gestational age there a few steps I would take as a sonographer. I would take biometric measurements (BPD, HC, AC, Fl) to see which parameters shows different gestational age than expected. I would take multiple measurement just to be safe. These measurements can determine if an asymmetric IUGR is present considering this typically becomes evident in the late second to thrid trimester. I would further asses the amnioitic fluid volume to see if there can be any contributing factors there affecting the babies growth. I also would perform the biphysical profile to asses how baby is thriving in its maternal environment and if preterm labor needs to be considered. A score of 6 and below after two biophysical assesments would mean that the mother needs to be admitted to be further evaluated. The assesment should be performed more than once just to make sure the baby is not resting. Furthermore, I would Doppler the ducuts venosus, cerebral artery, uterine artery, and umbilical artery to asses if blood if perfusing properly. Any qualitative apperances such as reverse diastolic flow, or quantitative values such as an umbilical artery with and S/D ratio above three can suggest the baby is not thriving in it its environment and needs to be delivered. Lastly of course as always, I would asses the cervix and placenta lie. 

This website has some great images of the third trimester protocal:

https://www.ultrasoundpaedia.com/normal-3rdtrimester/

I like this study because it reminds us of the various anomalies that can be present and how soon.

When noticing that the baby is measuring smaller, my next plan of action would be to remeasure the baby 2 additional times to confirm measurements are accurate. By measuring the BPD, HC, AC, and FL those will show us if baby is in fact measuring smaller than it should be and has IUGR. 

 There are two types of IUGR: symmetric and asymmetric. 

Symmetric is where all fetal biometric parameters tend to be less than expected (below the 10th percentile) for the given gestational age. Both length and weight parameters are reduced (HC/BPD and FL/AC)

Asymmetric is where some fetal biometric parameters are disproportionately lower than others, as well as falling under the 10th percentile. The parameter classically affected is the abdominal circumference (AC). HC/AC is useful because HC larger than AC. Asymmetric tends to occur in the 3rd trimester. Also fetal tachycardia (may be present in up to 50% of cases 4) and Oligohydramnios may be present as an additional sonographic feature.

 After remeasuring the baby I would then look at the amniotic fluid index by taking measurements of the deepest pockets of each of the 4 quadrants. Measuring the 4 quadrants in transverse and longitudinal planes while being perpendicular to the maternal spine is very important for accurate measurements. 

<5cm= oligohydramnios

>25 cm=polyhydramnios

 Next I would doppler the umbilical vein, ductus venosus, uterine artery, and cerebral artery to make sure blood was flowing appropriately. I would see if there are abnormalities present in these waveforms like a reversed A wave in the ductus venosus or high resistance in the umbilical artery instead of it being low.

 An S/D ratio for the maternal uterine arteries of below 2.6 is considered abnormal.

An S/D ratio for the middle cerebral artery under 3 is considered abnormal. 

An S/D ratio for the umbilical artery over 3 would be considered abnormal.

 Growth restricted fetuses with abnormal ductus venosus flow have worse perinatal outcome compared to those where flow abnormalities are confined to the umbilical or middle cerebral artery. If you see a reversed wave in the ductus venosus then the baby would need to be delivered since they are not thriving inside of mom. 

At this stage of pregnancy our main goal is to keep mom and baby safe leading up to delivery by making sure to be on the look out for instances that a pre-term delivery is necessary. We must pay close attention while scanning so we can prevent tragedies from occurring. 

Great job so far, friends! After reading Candee's post, here are some other questions I thought might be helpful to consider. 

Is there a difference between IUGR and measuring small for gestational age (SGA)? If so, what is it? How is it determined? Is there overlap between the two? Is there a different treatment or management plan for each? 

Before I take this PT in for their third- trimester follow- up exam, I would observe the priors to understand what I would expect during the exam. If I see that the fetus is measuring smaller than it should be, I would:

• ensure that I'm not pressing way too hard on the mother's belly, swishing the fetus's head smaller
• optimize the best windows to achieve a good view of biometric measurements
• take double the measurements ALWAYS to ensure accuracy

As sonographers, when we encounter a third trimester, the last phase of the pregnancy, we should be cautious of the fetal heartbeat, breathing/ body movement, Amniotic Fluid Volume, and most importantly the fetal weight! 

• M- mode,  normal fetal heartbeat should range from 110- 160 bpm
• Oligohydramnios 
  • < 200 ml
• Polygohydramnios 
  • > 2000 ml
• Intrauterine Growth Restriction (IUGR)
  • when the fetal weight is BELOW 10% of gestational age
  • Asymmetric--> occurs in the late second or third trimester
    • normal BPD/ HC, but small AC
  • Symmertic--> occurs in the first trimester
    • small BPD/ HC, AC, FL
• Macrosomia
  • birth weight is OVER the 90 percentile

I don't think our though process would significantly change. Just as Paris noted, before we ended class " [She] would scan in segments. As she takes images of the heart segment and can't image anything but LVOT, then it's incomplete". I believe that we are aware to stay cautious, vigilant, and scan as if this was our own baby. 

Hi everyone!

If I were to encounter a fetus measuring smaller than they should on their follow up scan, I would refer to previous exams and doctor's notes. If nothing corresponds with this smaller measurement, I may ask the parents just as a double checker if there is any family history of medical conditions that may explain what we're seeing.

After that, I would triple check all measurements, making sure not to overlook any discrepancies or human error while obtaining values. If the numbers still seem small, then it would point to some sort of IUGR. If this is confirmed, then there will be a lot more fine-toothed combing through the following exams and measurements up until birth. I would make sure fetus' heart is still beating, I would check mother's anatomy to make sure nothing new is happening health-wise, and I would check amniotic fluid levels, as well as doppler for blood flow patterns.

https://aium.org/resources/guidelines/obstetric.pdf  (pg5-7 goes through assessment in second and third trimesters in detail)

At this point in the pregnancy, we would also be looking at biophysical profiles to assess fetal well being. We also want to check for head or brain sparing from the IUGR.

Here's a diagram I found of possible features of IUGR:

Howdy everyone,

My first move would be to see if mom is unusually small. Then, I would double check my measurements. Am I on axis? Am I in the correct locations? If so, I'd move onto UA color and doppler. Is there good flow? If so, I'd check fluid, kidneys, and bladder. If the UA/V flow isn't great, I'd check the MCA.

At the third trimester baby should have had a 20 week scan and been checked off. Assuming measurements were normal at that time I'd assume something may be off. I'd take a quick biophysical profile in my head to see if I need to contact doctor right away.

Sarah

And that's all folks! Thank you to everyone for the participation this week. I know it is a busy one for us all as we prepare for finals. 

Here are some of the highlights from the discussion board:

- Third trimester follow ups are focused on evaluating the fetus's growth and ability to thrive for the remainder of the pregnancy. Fetal biometry is an essential component as always. 

- When the fetus is measuring < 10th percentile for EFW, SGA and IUGR are considerations. An IUGR diagnosis requires serial examination. 

- IUGR classically presents as symmetric or asymmetric.  In cases of suspected or diagnosed IUGR, spectral Doppler of vessels such as the UA, MCA, UV, and DV are important to monitor the fetus's well-being. 

- Taking mental notes if the fetus is checking the boxes for BPP during any 3rd trimester evaluation is a great practice, even if the exam isn't specifically a BPP.

- As always, take note of fetal lie, presentation, presence of a heartbeat, maternal anatomy, placenta and umbilical cord. Also, look at priors before the exam to give yourself a baseline.

I hope we all can continue to share our experiences and our expanding knowledge of OB going forward. I have learned something from all of you and I thank you!