First Trimester Anatomic Scan - HD

Introduction

Hello, I am Dr. Catherine Fong.

I'm an associate professor with the University of Toronto Department of Medical Imaging.

I'm also a staff radiologist at the Mount Sinai Hospital in Toronto, Canada, where I'm the co-director of the Center of Excellence in obstetric ultrasound.

I have a special interest in high risk obstetrical pregnancy and especially in the first trimester ultrasound.

My topic will be first trimester and atomic scan.

I have no financial disclosures.

Objectives

These are the objectives of my presentation to review early evaluation of fetal anomalies and potential diagnostic pitfalls to discuss how to improve detection of fetal anomalies in the first trimester, including the use of a standard protocol call.

Safety Issues in First Trimester Ultrasound

First of all, I would like to talk briefly about safety issues and first trimester ultrasound in the fetus.

We are most concerned about thermal effects.

The thermal index is a guide to the potential for tissue heating.

Now, bone absolves the most energy, so when the fetal bones ossified, we would use the thermal index of bone at gestational age more than 10 weeks.

So we need to monitor the output display when we are doing the ultrasound scan.

And here we have, indicated to you the thermal index for bone 0.4.

We should also use the allow principle as low as reasonably achievable.

That is using the lowest power output and the scan time needed to obtain diagnostic images.

A thermal index for bone of less than 0.7 is recommended.

Less than one is acceptable if the scan time is limited to less than 60 minutes.

We should also limit the transducer drought time in any one location as much as we can use MO or video to document cardiac activity and doppler should only be used if clinically indicated.

Fetal Structural Abnormalities

Now I'm going to move on to fetal structural abnormalities.

The major fetal anomalies can be broadly classified into three groups based on whether they can be detected at 11 to 13 weeks.

The first group are abnormalities that are always detectable.

The second group, those abnormalities that may be detectable, and the third group, those abnormalities that cannot be detected at 11 to 13 weeks.

Abnormalities Always Detectable at 11 to 13 Weeks

Now here I have listed six abnormalities that are always detectable at 11 to 13 weeks and this is an important slide.

Now, these six abnormalities are a cranial, a LoPro cephalic on IL gastroschisis, mastis, and, and body stalk anomaly.

We should make an effort to detect all of these abnormalities at the 11 to 13 week scan.

Let's look at some examples in this fetus.

We can appreciate that the shape of the fetal head is unusual and abnormal, especially when you compare with this normal fetus.

Now this finding of an abnormal fetal head shape should be noticed when we measure the crown rum length with a cranial in the first trimester there, there is usually a large amount of exposed brain tissue as you can see in this 12 week fetus.

Hence we use the term extensity.

However, as the gestation progresses, the the exposed brain tissue becomes absol.

So we have the situation of Acra.

In some cases of a cranial, the exposed brain can appear smooth and may appear normal.

As we can see in this coronal image of the fetal head.

An important ultrasound feature for making the diagnosis is the absent cranium, which is obvious.

When we compare with a normal fetus, we always do axial images of the fetal head to look for the cranial bone ossification.

In this 12 week fetus we can see the frontal and parietal bone ossifications even in a smaller fetus.

For example, in this 12 week fetus, we can see the frontal bone ossification.

Since cranial bone ossification is visible by 11 weeks, we therefore should be able to diagnose a cranial after 11 weeks gestation.

In this image we can also see the midline fox and also two choroids filling the lateral ventricles.

Now this would allow us to exclude a lobar hollow person cephalic.

This is a severe, the most severe form of harpo cephalic.

The Harpo cephalon is the full brain and this condition results from failure of courage of the full brain.

So we see a single midline ventricle replacing the two lateral ventricles.

This abnormality is often seen in fetuses with trisomy 13 and we would see the facial abnormalities as well such as the cleft lip and the SCUs.

Abdominal Issues and Examples

Now we'll be looking at some abdominal issues.

However, before we move on to IL and gastric diseases, we need to review some embryology, a physiologic, but gut herniation occurs at eight to 10 weeks and we can see an echogenic mass at the base of the umbilical cord in this 10 week fetus.

Due to physiologic mid gut herniation, by 12 weeks, the bowel would have moved into the normal position inside the abdomen.

So we have normal cord insertion here on Fallo seal should be diagnosed when a gestational age is more than 12 weeks.

When a mouse is bigger, more than seven millimeter and when it contains liver or stomach in this fetus, we can see bowel loops herniated through a defect in the anterior abdominal wall, usually to the right of the midline.

And we have a case of gastroschesis here.

Meti at 11 to 13 weeks is defined by a blood length of seven millimeter or more.

The incidence is one in 1500 pregnancies in approximately 30% of cases.

This condition is associated with ploidy, mainly trisomy 13 and 18.

However, in the eulo feeders, the prognosis depends on the bladder length.

If the bladder length is more than 15 millimeter, there is usually progression to severe obstructive neuropathy such as we have in this case of urethral atresia.

We can see hugely distended bladder I However, if the bladder length is between seven to 15 millimeter in 90% of cases, there is spontaneous resolution of the mega cys by 20 weeks.

So it's important to do a follow-up ultrasound to determine the significance of mega cystics.

'cause in some cases mega cys may be a transient finding.

BodyTalk anomaly is characterized by many abnormalities.

The fetus is usually distorted.

There is a large abdominal wall defect with herniation of the liver and bowel.

There is usually severe scoliosis and the com and the short umbilical cord.

Abnormalities That May Be Detected at 11 to 13 Weeks

Here I have listed some abnormalities that may be detected at 11 to 13 weeks and the detection rate, as you can see, is not a hundred percent for these abnormalities.

Many of these abnormalities such as diaphragmatic hernia, lethal skeletal dysplasia and congenital heart defects are associated with an increased nt.

And we'll come back to this later.

Abnormalities That Cannot Be Detected at 11 to 13 Weeks

Here I have listed some abnormalities that could not be detected at 11 to 13 weeks.

You can see agenesis of the corpus callosum, worming, hypoplasia, microcephaly, and many, many other abnormalities.

We are not able to detect them at 11 to 13 weeks.

Now some of the reasons why they are undetectable, Well first of all, because of embryologic development, some structures are not completely developed such as the corpus callosum and the cerebellum.

Some anomalies do not develop until later in gestation.

For example, some fetal tumors and some anomalies e evolve or progress over time so they become more obvious such as hypoplastic left heart syndrome.

The corpus callosum develops 14 to 18 weeks and it develops together with the septic pausity and the cavus SubT pausity.

So we often use the cave as a proxy for the corpus callosum.

Now in this clip of a 12 week fetus, if you notice, we don't see the cavem SubT pausity.

This is a normal finding.

If you look at the table here to your right, the gestational age of 15 weeks and 60% of the fetuses, the CSP is not seen.

So since non visualization of the CSP is a normal finding before 18 weeks, we will not be able to diagnose a genesis of the corpus callosum at 11 to 13 weeks.

Here I have two images of the posterior fossa.

We can see the cerebellar hemispheres and cord to this image.

We have a cleft in the cerebellar verus Now a cleft or so-called an open verus is a normal finding before 18 weeks, in this study by Bromley at all, at a gestational age of 14 weeks, the warmness is open in 56% of the fetuses.

Evolving Anomalies

Let's look at some evolving anomalies.

We were not able to diagnose this case of hypoplastic left heart at 12 weeks, but at 20 weeks we noticed that the heart is abnormal.

The left ventricle is much smaller than the right ventricle.

Accuracy of Ultrasound for Detection of Fetal Anomalies

What is the accuracy of ultrasound for the detection of fetal anomalies at 11 to 14 weeks gestation?

Well, this systematic review by Ross Etal reported an overall detection rate of 51%.

It is higher in the high risk population, 65% compared with the unselected population.

The high risk population includes mother with family history of previously affected fetuses, maternal age more than 35 years, fetuses with increased anti and abnormal karyotype.

In a more recent systematic review that was just published online, the detection rate for all anomalies in the low risk or unselected population was a bit lower at 32% instead of 51%.

But the detection rate remains high in the high risk population at 61%.

A second trimester scan was part of the protocol in many of the studies and it detected additional anomalies in the low risk or unselected population.

The second trimester scan detected 60% of all fetal anomalies detected antenatally.

So the first trimester, an atomic scan does not replace the second trimester scan.

Benefits of the Early Anatomy Scan

What are be the benefits of the early anatomy scan?

Well, early identification of abnormalities allows the option of earlier counseling and diagnostics diagnostic testing as well as early management options.

For women who are at high risk of having an effective fetus, a normal first trimester scan could provide them early reassurance.

This patient has a previous affected pregnancy with Macal syndrome.

We see ence cell poly and enlarged cystic kidney.

She came back for an early scan During the current pregnancy, we did not see any of these abnormalities and we were able to reassure her that the fetus was not affected.

Improving Detection of Fetal Anomalies

Now I'd like to move on and discuss factors that allow us to improve the detection of fetal anomalies at 11 to 13 weeks.

Transvaginal vs. Transabdominal Scanning

First question that I was often asked is when should we do the transvaginal scan?

Well, we usually start the scan by using the transabdominal probe, which is easier to maneuver and preferred for anti measurement.

However, in mother in mothers with high body mass index or a retroverted uterus, we would not spend a lot of time with the transabdominal scan but would move on to the transvaginal scan.

This was a difficult scan because of large maternal body habitus.

Even though the NT was normal because the sonographer could not see the feet as well, she went on to do TRANSVAAL scan.

We can see that the resolution is better and sagittal and transverse images show a large meningo cell with open spinal pivotal in the lumbar sacral region.

In this 12 week fetus, the fetal head was not well seen, so we do transvaginal scan and it confirmed a cranium.

Now this fetus on the transabdominal scan, it was not clear if there was an anterior abdominal wall mass, but on the transvaginal scan it is quite obvious that there is a one centimeter mouse protruding from the anterior abdominal wall due to PHA cell.

Education, Training, and Timing

We would now discuss about factors such as education and training and the timing of ultrasound.

There is a learning curve for the detection of fetal anomalies and the detection rate depends on experience here from this graph we can see that with education and training there is an increase in the detection rate of major fetal anomalies by midwives over a period of several years.

What about, what about the timing of ultrasound?

Gestational age is important.

We can see from this graph that the detection rate increases from 11 weeks to 14 weeks gestation.

It is a little bit difficult to evaluate fetal anatomy at 11 weeks, but it is much easier to assess the 13 to 14 week fetus.

Recognizable Markers: Nuchal Translucency (NT)

We also look for easily recognizable markers to identify the high risk room and I will be discussing NT and it.

This fetus has an increased NT 4.2 millimeter, but the chromosomes were normal.

So what are the chances that the baby will be normal?

If we look at this table, we can see that when the nucle translucency thickness increases, there is an increased prevalence in adverse outcomes and these include chromosomal defects, fetal death, and major fetal abnormalities.

As anti increases the chances that the baby will be alive and wealth decreases as you can see from 93% with an NT between 95 to 99 percentile to 15% when the NT measures more than 6.5 millimeter.

There are several possible mechanisms for the pathophysiology of increased nt.

They include cardiac defects or dysfunction venous congestion in the head and neck due to superior mediastinal obstruction and, and we see that when we have a narrow thorax in lethal skeletal dysplasia or when we have a space occupying lesion in the chest such as diaphragmatic hernia.

Another mechanism is failure of lymphatic drainage either because the lymphatic system is abnormal such as internal syndrome or because there is reduced fetal movements in neuromuscular disorders.

And then other mechanisms include altered composition of the extracellular matrix, fetal anemia and high-protein anemia.

This fetus has an increased NT of over five millimeter, this four chamber view of the heart.

In this four chamber view, we can see that the heart is abnormal with a large atrial ventricular septal defect.

Now this video clip shows you the large atrial ventricular septal defect and there was only a single AV valve and we can see that the valve is opening and closing on the clip.

This meta-analysis of 20 studies, reported that when the NT is more than 95th center, the sensitivity for detecting major congenital heart defects is 44% with a specificity of 95% and an increased NT of more than 99 centile is associated with a positive likelihood ratio of 30.5.

In other words, an increased NT more than 99 cent hour is associated with a more than 30 times increased risk of major congenital heart disease.

So when we see increased NT and especially normal karyotype, We would do a detailed anatomic scan to look for fetal structural abnormalities including major cardiac defects, skeletal dysplasia, diaphragmatic hernia, fetal kinesia deformation sequence, and many, many other abnormalities, as well as single gene disorders and genetic syndromes such as newnan syndrome.

So an increased NT is an indication for a detail and atomic scan and fetal echocardiography.

Intracranial Translucency (IT) as a Marker

I'm going to move on to a new relatively new marker, the intracranial translucency.

This was first described by Shahi atal for the detection of spina bifida at 11 to 13 weeks.

So why do we need a new marker?

Well, the cranial signs that we are familiar with the lemon and banana signs.

Unfortunately, we often don't see them this early in gestation.

So, Dr. Shahi proposed this new marker in this mid sagal image of the fetal head.

We can see the thalamus, the midbrain, and the brainstem.

Behind the brainstem there is a fluid filled area.

This is the fourth ventricle, also referred to as the intracranial translucency.

In a retrospective study, when the intracranial translucency was seen open spina bidu could be reliably excluded.

However, in cases with open spina bidu, the intracranial translucency was not seen.

So it was postulated that the Q2 malformation was already present in the first trimester.

However, further observation show that in some cases of open spine and bifida, even though a typical it was not seen, there is some fluid behind the brainstem and this could be confusing.

So let's review the landmarks of the normal posterior brain.

That should be four white lines.

The anterior border of the brainstem, the posterior border of the brainstem, the choroid plexus and the occipital bone.

So between the first two lines, we see the brainstem between the posterior border of the brainstem and the choroid plexus.

We see the intracranial translucency between the Cory plexus and the occipital bone.

We have another fluid collection and this is the futu cy sternal mag.

So let's look at this clip of a normal trial, weak feeders, and we can see the landmarks that we have just discussed.

This is the brainstem.

Behind it is the intracranial translucency, and then behind that is another fluid collection.

The future cisterna magnum just anterior to the frontal bone.

Now this is often the same image that you would use to measure the nuc nuclear translucency thickness in a normal fetus.

We can also appreciate that the brainstem is shorter compared with the brainstem occipital bone distance.

And there has been a study reporting the ratio of these two diameters in fetuses with open spina bifida.

There is posterior and downward shift of the posterior brain and this results in thickening of the brainstem and shortening of the brainstem occipital bone distance.

So compare this normal brainstem, thin brainstem in a normal fetus with the relatively thick brainstem in the fetus with open spina bifida.

A recent report of this prospective multicenter Berlin, it study reported in over 16,000 fetuses scanned by 20 ultrasound experts.

There were 11 cases of open spina vida.

The detection rate was a hundred percent.

Eight cases were detected at the first examination and three cases were considered suspicious.

At the first examination where the lesion detected a few weeks later, the paper concluded that in the hands of an expert open spinal BI can be reliably diagnosed at 11 to 14 weeks.

However, we have some unresolved issues.

For example, the Berlin IT study did not report the false positive rate, if any, and the results cannot be generalized.

So perhaps we need further perspective studies, but more importantly, I think before we introduce this technique into, wide use Is important to, concentrate on specific operator training and quality assurance.

Meanwhile, we can get used to looking at the posterior brain and if it appears abnormal, such as in this feeders where we don't identify, don't see any of the normal landmarks, the four lines that the brainstem appears thick and the it and sternal magner either the IT or the Cy Magna cannot be seen, then we should suspect open spinal bi.

And it's important to do a detailed look at the spine.

So we did that and we search and found the open spinal BI at 13 weeks in this 13 week feeders in the lumbar spine area.

Standard Anatomic Protocol

Finally, to improve detection, we should use a standard anatomic protocol is walk.

The International Society of Ultrasound and Obstetrics and Gynecology have published practice guidelines for the performance of first trimester fetal ultrasound scan.

And this protocol was proposed for the evaluation of fetal anatomy at 11 to 13 weeks.

Now, many of the structures listed here are compulsory or required, but those structures that have an asterisk are optional At our institution, we have incorporated a basic fetal anatomy into the anti scan scan and our sonographers would obtain several routine views for the evaluation of fetal anatomy.

So in this sagittal view, which we use for crown rum length measurement, we can see the fetal bladder and in this case it looks normal.

When the bladder looks the standard, then we would measure it.

We would do axial images of the cranium and the brain to look for the cranial bone ossification, the midline fox, and the choroids and ventricles.

We would do an axle view of the abdomen to look at the court insertion site and the inter abdominal wall, And we would image all four limbs with three segments in each of the limbs.

Future Role of First Trimester Ultrasound

Looking into the future, we should have answers ready for this important question.

What will be the role of first trimester ultrasound if cell-free DNA screening for PL becomes routine should we abandon the 11 to 13 week scan?

Well, I think there are several reasons that we should not abandon the 11 to 13 week scan, and these reasons are to clarify the cell-free DNA results for the detection of fetal structural abnormalities, either using increased NT as a marker or to do your comprehensive anomaly scan.

And also for optimal obstetrics care, we need to do the 11 to 13 week scan to look for fetal viability for accurate dating and in multiple pregnancies.

We need to determine ity and amity looking at the uterus and annexer and also, perhaps in the future uterine artery doper for preeclampsia screening.

Thank you for your attention.