Screening for the common autosomal trisomies has been a cornerstone of obstetric care over the past 4 decades.1,2 Although important, it is essential to recognize that aneuploidies represent only a small portion of the total fetal genetic and structural risks. Congenital malformations occur in 3–5% of births and are associated with genetic abnormalities and death.3–5 The combination of cell-free DNA screening and early anatomic imaging has been demonstrated to have a higher detection rate for abnormalities in the latter part of the first trimester than either method alone.6–10 Although 25–50% of structural malformations have an identifiable genetic cause, it is expected that the percentage attributable to a genetic cause will increase with our rapidly expanding use of next-generation sequencing.11–17

In this Clinical Expert Series, first-trimester obstetric ultrasound examination refers to an ultrasonographic examination performed at the end of the first trimester, which is the first opportunity to consistently assess the fetal structural anatomy.18,19 Technologic advances and ultrasonographer–physician experience in fetal imaging have led to significant improvements in our ability to distinguish between normal and abnormal fetal structural development in the latter part of the first trimester. In addition, findings on a first-trimester anatomic ultrasonogram may affect the choice of genetic testing in 9.6–16.1% of pregnant patients.20,21 For example, some fetuses may not have cardiac activity, may be smaller than expected for dates, or may be part of a multiple gestation. Moreover, a fetus may have an enlarged nuchal translucency or structural anomalies that should prompt genetic counseling and discussion of diagnostic testing instead of screening alone. Foregoing the opportunity to evaluate the fetus at the end of the first trimester results in suboptimal use of cell-free DNA screening and in the delayed detection of many birth defects and genetic conditions until the second-trimester anatomic survey or later, potentially reducing the quality of care for pregnant individuals and possibly limiting their reproductive options, including pregnancy termination.6–10,20–23

HISTORY

Screening for aneuploidy with the nuchal translucency was reported by Nicolaides et al in 1992.24 By the mid-2000s, combined screening for aneuploidy at the end of the first trimester, with a precise measurement of the nuchal translucency and crown–rump length in conjunction with serum analytes, became the standard of care.25–27 The Fetal Medicine Foundation was the first organization to credential and monitor individuals performing the nuchal translucency.28 In 2005, the Nuchal Translucency Quality Review program was established to provide education, credentialing, and epidemiologic monitoring to optimize ultrasonographer and physician–ultrasonologist performance in measuring the nuchal translucency accurately.27,29 Over the ensuing 18 years, the Nuchal Translucency Quality Review program credentialed and monitored more than 10,000 individuals, demonstrating its ability to establish, maintain, and improve the performance of high-quality nuchal translucency measurement among a large group of imagers.30

In October 2011, cell-free DNA screening for the common autosomal trisomies was introduced into clinical care, with markedly improved test performance metrics in both singleton and twin gestations.31–33 Nationally, the rapid adoption of cell-free DNA screening for aneuploidy has led to a decline in the use of screening paradigms that require a precise measurement of the nuchal translucency and a decrease in the number of patients receiving first-trimester ultrasound examinations.34,35

Ultrasound examination before cell-free DNA has been shown to be cost effective, and societal guidelines in the United States have suggested that obstetric ultrasound examination may be useful before cell-free DNA screening.1,22,36 However, American College of Obstetricians and Gynecologists and Society for Maternal-Fetal Medicine guidance documents additionally state that a nuchal translucency measurement for aneuploidy risk assessment is not necessary at the time of cell-free DNA screening in the first trimester and do not support first-trimester ultrasound examination for the sole purpose of measuring the nuchal translucency in pregnant individuals with a negative or low-risk cell-free DNA result.36 Furthermore, some payers are not reimbursing for a “nuchal translucency” ultrasound examination (Current Procedural Terminology code 76813) in the setting of cell-free DNA screening for aneuploidy.

USING ULTRASOUND TO DETECT CONGENITAL ANOMALIES IN THE FIRST TRIMESTER

Increased operator experience, along with improved resolution of ultrasound imaging systems and the use of transvaginal ultrasonography, has tremendously expanded our ability to assess fetal structural anatomy in the latter part of the first trimester.37 Although imaging protocols vary by international, national, and societal recommendations, even a standard (minimum) fetal anatomic evaluation will identify a significant proportion of major fetal malformations.38–45 With the use of a standardized detailed anatomic template in the first trimester, approximately half of structural anomalies can be identified in singleton pregnancies.46–50 In a population of more than 100,000 pregnancies, Karim et al48 demonstrated that the pooled detection rate of all fetal anomalies was 32.4% in a low-risk or unselected population (46.1% major anomalies) and 61.2% in a high-risk population. These investigators and others have demonstrated that the detection rate of anomalies is enhanced by the use of a standardized imaging protocol and that there is a trend between the use of an increasingly detailed protocol and higher anomaly detection rates.48,51,52 Similarly, detection rates of any malformation are higher in fetuses with multiple malformations.47 In a retrospective study using prospectively collected data and after exclusion of fetuses with aneuploidy, the overall detection rate of anomalies in the first trimester anatomic survey was 27.6%.53 The proportion of anomalies detected in dichorionic twin gestations without known aneuploidy appears to be similar to that of singletons (27.1%), with higher rates in monochorionic twin gestations (52.6%), which is likely attributable to the higher prevalence of malformations and the added contribution of abnormalities related to the timing of zygote division.54 Notably, some anomalies are more amenable to detection than others and are identified in almost all situations, whereas others are potentially detectable by an experienced clinician, and still others are not diagnosable in the later first trimester.47,50,53,55

EARLY ANATOMIC IMAGING PROTOCOLS

The nationally available imaging protocols in the United States include the Standard Diagnostic Obstetrical Ultrasound Examination, which outlines the minimal key elements required for a fetal anatomic assessment that can be performed by a variety of clinicians in a range of practice settings across the country.38 It is recognized that some patients are at an elevated risk for abnormalities and may benefit from an “indication-driven” detailed first-trimester ultrasound examination performed by subspecialists in fetal imaging.39

This approach is somewhat different from that of our international colleagues, who have published a single document, “ISUOG Practice Guidelines (Updated): Performance of 11–14-Week Ultrasound Scan,” with two checklists for the assessment of fetal anatomy between 11 and 14 weeks of gestation.40 The first is to establish the minimum required components, and the second is more detailed and represents best practice. The minimum requirements of the International Society of Ultrasound in Obstetrics and Gynecology guideline are more comprehensive than the standard examination in the United States, whereas the detailed examination is similar among organizations, with the most notable exception being that the International Society of Ultrasound in Obstetrics and Gynecology document considers cell-free DNA screening a second-tier screening after first-trimester combined screening and includes an evaluation of preeclampsia risk.40 Regardless of the differing anatomic protocols, widespread implementation within most countries is inconsistent and suboptimal.45

The Standard First-Trimester Anatomic Scan (Minimum)

The “ACR-ACOG-AIUM-SMFM-SRU Practice Parameter for the Performance of Standard Diagnostic Obstetric Ultrasound Examinations” includes a list of structural components that represent the minimum key elements of an obstetric ultrasound examination outside of a limited setting (emergency or follow-up)38,56 (Table 1). Adhering to these minimal standards will detect a significant number of major structural anomalies42–44,48,53 (Appendices 1–4, available online at https://links.lww.com/AOG/D653, and Figs. 1–4). Although not listed in this standard practice parameter, we consider evaluation of the fetal bladder an important anatomic landmark that should be routinely included. Any concerns about abnormal anatomy on a standard first-trimester obstetric ultrasound examination should be followed up, preferably with a detailed first-trimester obstetric ultrasound examination.39,57

Table 1.:

Standard First-Trimester Obstetric Ultrasound Examination (Approximately 11 0/7–13 6/7 Weeks of Gestation)*†

Fig. 1.:

A. Axial scan through the fetal brain (transvaginal) at 13 weeks of gestation showing a monoventricle (arrows) and fused thalami characteristic of alobar holoprosencephaly. B. Modified coronal view of the same fetus showing microphthalmia and hypotelorism (yellow arrows) and a proboscis (white arrow). C. Corresponding 3-dimensional surface rendered imaging showing the proboscis (arrow). This fetus had trisomy 13.

Fig. 2.:

A. Sagittal scan through the fetus at 12 weeks of gestation demonstrating a solid mass (arrows) disrupting the abdominal wall characteristic of a liver containing omphalocele. B. Axial scan across the abdomen of the same fetus showing the stomach (St) and abdominal contents (arrows) disrupting the anterior abdominal wall.

Fig. 3.:

Axial scan through the abdomen of a 12-week fetus showing the abdominal umbilical cord insertion (UCI) using color Doppler flow imaging. Adjacent to the cord insertion is a heterogeneous lobulated mass (white arrows) characteristic of a gastroschisis. Note the output display standard (yellow dotted box) demonstrating thermal index type and ratio, compliant with ALARA (as low as reasonably achievable) principle.

Fig. 4.:

Sagittal scan of a fetus at 12 weeks of gestation demonstrating an echolucent fluid collection extending from the fetal pelvis into the abdomen. This was confirmed to be the fetal bladder according to the location of the umbilical arteries (not shown). The longitudinal bladder length is 19 mm (megacystis). This degree of distension is characteristic of lower urinary tract obstruction.

False-positive and false-negative imaging findings may occur in any screening program, related to the natural history of the observed finding or the experience of the performing and interpreting clinicians.58–60 When these cases arise, it is imperative that a retrospective review of images for quality assessment and practice improvement be conducted.

The Detailed First-Trimester Anatomic Scan

The detailed first-trimester ultrasound examination is a comprehensive evaluation of the fetus that is currently indication driven and performed in patients at increased risk for anomalies based on clinical history or an abnormal standard first-trimester assessment, including an enlarged nuchal translucency.39,57,61 The components of a detailed first-trimester ultrasound examination are outlined in the “AIUM Practice Parameter for the Performance of Detailed Diagnostic Obstetric Ultrasound Examinations Between 12 Weeks 0 Days and 13 Weeks 6 Days”39 and are considerably more extensive than those included in the standard examination.38 The detailed first-trimester ultrasound examination includes, among other anatomic features, an extended evaluation of the fetal heart, including the four-chamber view and outflow tracts with color or power directional Doppler. This ultrasonographic examination is performed by ultrasonographers and physician–ultrasonologists with extensive obstetric imaging experience (typically maternal–fetal medicine physicians) who meet the training guidelines for performing detailed anatomic examinations in the second trimester and have further educational and volumetric experience in detailed first-trimester ultrasonographic examinations.62 It is expected that the ultrasonographer and interpreting physician are adept at optimizing image quality, using color and spectral Doppler (while adhering to the “as low as reasonably achievable” principle), performing transvaginal ultrasonography and 3-dimensional imaging.39,63,64

Use of a Detailed First-Trimester Ultrasound in Unique Populations

Early detailed anatomic imaging is a helpful tool to image the fetus in pregnant patients with obesity. Elevated body mass index (BMI, calculated as weight in kilograms divided by height in meters squared) is seen in 39.7% of women of reproductive age and is associated with an increased risk of structural anomalies such as neural tube defects, congenital cardiac anomalies, and orofacial clefts.65,66 Early fetal evaluation can be performed while the uterus is beneath the panniculus, and transvaginal imaging is an option to improve visualization. In these circumstances, a detailed early anatomy scan provides a complementary modality to the second-trimester anatomic assessment, often allowing completion of the anatomic evaluation earlier in gestation.67–70

The detailed first-trimester ultrasound examination also includes a thorough evaluation of the placenta for placenta accreta spectrum in patients at risk for this condition, including those with a history of cesarean delivery and a low anterior placenta or cesarean scar ectopic pregnancy on an earlier ultrasonographic examination.71

ROLE OF THE NUCHAL TRANSLUCENCY IN THE ERA OF CELL-FREE DNA SCREENING

A subjective examination of the nuchal region is a component of all first-trimester imaging protocols. In the United States, a precise measurement of the nuchal translucency is recommended if it is being used for combined screening for aneuploidy or if it subjectively appears enlarged.38,39 International guidelines support the routine measurement of the nuchal translucency as an important feature to stratify risk.40 There is no uniform consensus as to what constitutes an enlarged nuchal translucency. The width of the nuchal translucency increases by crown–rump length. Various thresholds have been used to define an enlarged nuchal translucency, including nuchal translucency of 95% or more or nuchal translucency of 99% or more for crown–rump length; however, in many cases, a numeric threshold of 3.0 or 3.5 mm is used for ease of implementation in the clinical setting. The American College of Obstetricians and Gynecologists refers to an enlarged nuchal translucency as a threshold of 3.0 mm or more or 99% or more for crown–rump length, but these are not equivalent demarcations.1 Although the majority of common autosomal trisomies can be excluded by a cell-free DNA analysis, an enlarged nuchal translucency is also associated with an increased risk of other genetic abnormalities such as rare autosomal trisomies, submicroscopic abnormalities, and single-gene conditions, as well as structural malformations and fetal death.8,72–75 These risks increase with progressive enlargement of the nuchal translucency.76

The most common structural anomalies associated with an enlarged nuchal translucency are cardiac malformations, many of which can be identified in this early gestational age range.77–79 In a recent systematic review and meta-analysis of first-trimester detection of fetal heart anomalies including more than 300,000 fetuses, the pooled sensitivity for the detection of major cardiac defects in the first trimester was 55.8% in the non–high-risk population and 67.7% in the high-risk population.51 The detection rate was significantly enhanced in imaging protocols evaluating the outflow tracts and using color Doppler for the cardiac examination and with experienced ultrasonographer–ultrasonologists.51,78,79

American College of Obstetricians and Gynecologists and American Institute of Ultrasound in Medicine guidance suggests that a second-trimester fetal echocardiogram may be considered with an nuchal translucency of 3.0–3.4 mm and is recommended if the nuchal translucency is 3.5 mm or greater.1,80 The American Institute of Ultrasound in Medicine also considers an nuchal translucency of 99% or more for crown–rump length as an indication for fetal echocardiography. Jelliffe-Pawlowski et al75 have shown that using a threshold of a nuchal translucency of 99% or more for crown–rump length is associated with a greater than 200% increase in detection of critical congenital heart defects above that obtained by using a threshold measurement of 3.5 mm but is associated with an increase in the false-positive rate from 0.2% to 1.1%. All extracardiac malformations combined are more common than cardiac anomalies alone and include malformations such as orofacial clefts, congenital diaphragmatic hernias, and exomphalos, among many others.

The nuchal translucency threshold at which to offer diagnostic testing, including chromosomal microarray, is not well established. The incremental detection rate of clinically significant chromosomal microarray findings depends on the extent of cell-free DNA screening and the threshold used for defining an enlarged nuchal translucency, which is not uniform. Patients with an enlarged nuchal translucency should be offered genetic counseling with discussion of residual risk and diagnostic testing options. The International Society for Prenatal Diagnosis recommends a threshold of 3.5 mm for offering diagnostic testing.81 A meta-analysis by Grande et al72 reports an added yield of 4.0% for isolated enlarged nuchal translucency (typically 3.5 mm or greater) and 7.0% when other malformations were present. The most common pathogenic copy number variant reported was a deletion or duplication of 22q11.2. The pooled prevalence of variants of unknown significance was 0.8%.

Although there is no consensus for recommending diagnostic testing with other nuchal translucency thresholds, a clinically significant copy number variant has been reported in 4.7% of fetuses with an isolated nuchal translucency between 3.0 and 3.4 mm with a variant of unknown significance in 0.8%.82,83 In this population, use of cell-free DNA screening for the major autosomal trisomies and sex chromosomes would have resulted in a residual risk of 1.9% for significant copy number variants.82 Bardi et al73 reported that among fetuses with a nuchal translucency of 95% or more for crown–rump length, 23.9% had trisomy 21, 18, or 13; 5.4% had other karyotype abnormalities; 2% had an abnormal chromosomal microarray; and 2% had a single gene disorder. Furthermore, an isolated structural anomaly was identified in 9.3% of fetuses with a normal chromosomal microarray, almost half of which were seen before 14 weeks of gestation.73

Berger et al84 demonstrated that the addition of nuchal translucency screening at a threshold of 3.0 mm or greater would identify 16.6% of rare aneuploidies; however, the positive predictive value of this finding was 2.6%, and the authors calculated the need to screen 4,176 fetuses by nuchal translucency to detect a rare aneuploidy. In those with an enlarged nuchal translucency (isolated 5.0 mm or more, or 3.5 mm or more with other selected anomalies) and normal chromosomal microarray, reflex testing for RASopathy (eg, Noonan syndrome) should be discussed.85,86 The added yield of next-generation sequencing in the setting of an isolated enlarged nuchal translucency remains to be established.87,88

In a fetus with an enlarged nuchal translucency, if a structural anomaly is not identified at the end of the first-trimester assessment, an early second-trimester ultrasound examination at approximately 16 weeks of gestation may be considered, because there is an incremental increase in the detection of anomalies on ultrasonography at that time.89 In euploid fetuses with a nuchal translucency 3.5 mm or more, an incremental anomaly detection rate of 41.2% has been reported, including multiple malformations, cardiac defects, and diaphragmatic hernia.89 In addition, a detailed structural survey typically performed between 18 and 22 weeks of gestation and fetal echocardiogram as indicated are recommended by professional societies.80,90

CONGENITAL ANOMALIES DETECTED IN THE FIRST TRIMESTER

When structural anomalies that can be detected by ultrasound examination in the first trimester are categorized, there are some anomalies that are “almost always” detectable, including abnormalities such as acrania, alobar holoprosencephaly, cystic hygroma, hydrops, ectopia cordis, large exomphalos, gastroschisis, amniotic band sequence or body stalk anomalies, and megacystis (Appendices 1–4, https://links.lww.com/AOG/D653) (Figs. 1–4).53–55 These anomalies almost always should be identified when a standard anatomic imaging protocol is followed.38,40 Similarly, in monochorionic twins, anomalies such as conjoined twins and twin reversed arterial perfusion sequence are readily identified in the first trimester.54 Other anomalies are potentially detectable, including micrognathia and limb anomalies50,53,60 (Appendix 5, available online at https://links.lww.com/AOG/D653) (Fig. 5). Malformations such as spina bifida, posterior fossa anomalies, facial clefts, and congenital diaphragmatic hernias have lower detection rates, although many visual clues can aid in their identification. For example, an abnormal appearance of the fourth ventricle (intracranial lucency) or cisterna magna on a midsagittal view of the fetal head or a gap in the maxilla on a median view of the profile can be observed60 (Fig. 6). It is important to note that some ultrasonographic findings may be concerning in the first trimester such as megacystis (bladder length 7–15 mm), bowel containing omphaloceles, intra-abdominal cysts or fluid collections, and some cardiac anomalies in euploid fetuses that may potentially resolve without adverse outcomes.53,59,91–93 As would be expected from embryologic development, some malformations are almost never detected in the first trimester, including agenesis of the corpus callosum, microcephaly, lissencephaly, and congenital pulmonary malformations53 (Table 2).

Fig. 5.:

Midsagittal profile view of a 12-week fetus showing retromicrognathia (arrow) in a fetus with Pierre Robin sequence. The micrognathia can be more pronounced early in gestation.

Fig. 6.:

Transvaginal imaging of the fetal face in a patient with a body mass index (BMI) of 40 at 13 weeks of gestation. Incomplete fetal assessment by transabdominal imaging prompted transvaginal evaluation. A. Sagittal view of the fetal profile. The nasal bone is present, but the maxilla has a large gap (arrow). B. Axial scan through the fetal palate showing the hypoechoic defect (arrow) in the primary palate (cleft palate). The dot seen on the palatal defect in images A and B represents a single point in space demonstrated in orthogonal planes by three-dimensional multiplanar reconstruction. C. Three-dimensional surface rendering in the same fetus defines the skin surface defect of the unilateral complete cleft lip (arrows).

Table 2.: Anomalies That May be Detected on Standard Late First-Trimester Obstetric Ultrasound Examination*,50,53,54

Genetic counseling and diagnostic testing (typically with at least chromosomal microarray) are a uniform recommendation for a patient whose fetus has a structural malformation.12,13,94–96 Next-generation sequencing is recognized as providing additional genetic information in at least 8–10% of fetuses with anomalies with substantially higher detection rates among those with multisystem anomalies, skeletal dysplasias, or nonimmune hydrops; however, the counseling is nuanced and complex, and studies are costly and not universally covered by insurance.13–17 Structural anomalies and copy number variants may occur in 1–2% of fetuses with low-risk cell-free DNA results or normal nuchal translucency measurements.97–99

In patients with a high-risk cell-free DNA screen, diagnostic testing for confirmation is recommended, recognizing that an early anatomic scan in which a major anomaly is identified will increase the positive predictive value of an abnormal result.100,101 For fetuses suspected as having trisomy 18, trisomy 13, or monosomy X, an early detailed anatomic assessment may be helpful in guiding the choice of diagnostic testing (chorionic villous sampling or amniocentesis) because of concerns about confined placental mosaicism.102

REPRODUCTIVE IMPLICATIONS OF FIRST-TRIMESTER ULTRASOUND EXAMINATION

It is particularly critical to point out the importance of our comments in the post-Dobbs era [U.S. Supreme Court decision Dobbs v. Jackson Women’s Health Organization, Docket No. 19-1392; 597 US__(2022)]. Identification of a structural anomaly or enlarged nuchal translucency provides the opportunity for genetic counseling, diagnostic testing, including next-generation sequencing, and multidisciplinary consultation to obtain as much information as possible in a timely manner. Earlier availability of comprehensive information supports the thorough and thoughtful consideration of reproductive options and safer choices, including selective reduction in multiple gestations and termination of pregnancy when desired.103–109 It is essential to provide early anatomic assessment across communities and practice settings to support equity in health care. The burden of a later anatomic diagnosis of a structural abnormality should not be determined by social or economic metrics.

INTEGRATING THE FIRST-TRIMESTER ANATOMIC SCAN INTO CLINICAL PRACTICE

Obstetrics and gynecology specialists performing or interpreting the standard obstetric ultrasound examination in the first trimester should meet the training guidelines required by the American Institute of Ultrasound in Medicine and should be familiar with the nuances of first-trimester anatomic imaging, including the “as low as reasonably achievable” principle.60,62–64 Ultrasonographers credentialed by the American Registry of Diagnostic Medical Sonography in obstetric ultrasonography with appropriate training can perform a fetal anatomic assessment at a level that is more comprehensive than the current standard protocol and, undoubtedly, with focused training and experience can perform a detailed first-trimester ultrasound examination.19 When the fetus is evaluated, an attempt should be made to visualize additional anatomic structures and to become familiar with extended views.

In most cases, a 30-minute time slot should be adequate to complete a standard examination.50,53 Experience has shown that 12.5–13.5 weeks of gestation is the optimal time to perform an early anatomic assessment study, resulting in the highest anomaly detection rate with fewest number of patients requiring transvaginal imaging to facilitate completion of the evaluation.18,47 If required anatomic elements are not seen well transabdominally, if an anomaly is suspected, or if there is an enlarged nuchal translucency, transvaginal imaging is suggested because it optimizes the detection of anomalies. Some practices routinely use the transvaginal approach in the anatomic evaluation of the fetus in the first trimester because it enhances visualization of some anatomic structures, including the fetal kidneys.

Although performance of cell-free DNA screening at the time of the early anatomic ultrasound examination facilitates optimal use of screening and diagnostic testing, it delays the detection of major autosomal trisomies by several weeks. Many practices in resource-rich environments perform the cell-free DNA screening at 10 weeks of gestation. Patients with high-risk results are triaged to detailed first-trimester ultrasound examination, genetic counseling, and diagnostic testing if desired. The majority of patients will have a low-risk result, can be reasonably reassured, and are scheduled for an early anatomic assessment on the basis of other indications at 12.5–13.5 weeks of gestation. The described process streamlines the early detection of autosomal trisomies, although it is recognized that, in a small number of pregnancies, results may not be obtained or may not provide substantial benefit (eg, early pregnancy loss or fetal anomaly). Pretest counseling is paramount for the patient to understand the sequential steps in risk stratification of the fetus to recognize that some anomalies may not be detected until later gestation or even after birth.

In studies addressing patient preference regarding timing of diagnosis of structural anomalies, pregnant people desire to be informed as early as possible about the presence or absence of structural anomalies.110,111 In those choosing to terminate a pregnancy for a fetal anomaly, psychological trauma of an earlier termination may be less than that experienced by those terminating later in gestation.104,105 Billing for the standard first-trimester anatomic ultrasound examination is based on Current Procedural Terminology code 76801. Billing for the indicated detailed first-trimester ultrasound examination is in the process of societal evaluation, with a recommendation forthcoming.

In an ongoing pregnancy, the performance of an early anatomic examination must be followed up by a second-trimester standard or detailed anatomic assessment of the fetus (depending on indication) because some anomalies may not be detected until later in gestation or after birth.38,53,90

CONCLUSION

Autosomal trisomies reflect a small portion of the total genetic and structural risk to the fetus, particularly in younger patients. The early anatomic scan, even at the standard level (minimum key elements), is a vital component of pregnancy care. If pregnancy screening is limited to cell-free DNA alone, many anomalies will not be identified until the second-trimester anatomic survey, including more than half of those in the “almost always” detectable category.23 In patients at increased risk for an abnormality, a detailed first-trimester ultrasound examination should be performed if resources are available.39,57 Although a normal early anatomic scan will provide some reassurance to the majority of individuals, the early identification of a fetus at risk for genetic or structural malformations allows the opportunity for genetic counseling and time to obtain results from expanded genetic testing and multidisciplinary consultation, thus maximizing the information that a pregnant person and their family have to consider their reproductive options and to obtain the safest care.103,108 We agree with our international colleagues that congenital anomalies commonly occur without recognized risk factors, and we should strive to incorporate a more comprehensive examination of the fetus into our standard scanning protocols, thus optimizing the detection of anomalies. We recognize that a first-trimester anatomic scan is the right thing to do; however, it must be performed and interpreted by appropriately trained ultrasonographers and physicians, fiscally sustainable, and offered to all patients, promoting equity in reproductive opportunities. In our opinion, implementation of the standard first-trimester screening examination is an absolute minimum threshold that we must strive to achieve while encouraging ourselves to look at the fetus more comprehensively.38–41,45 The expertise gained by the ultrasonographer or ultrasonologist while attempting to obtain more detailed additional views of the fetus during an ultrasonographic examination will ultimately lead to enhanced imaging skills and improved detection of structural malformations. Similar to our enriched observations while performing the basic nuchal translucency scan, the improved detection of structural anomalies is anticipated to result in a shift in the paradigm of prenatal screening algorithms. It is recognized that in the current era, there are significant national barriers to implementing screening for fetal anomalies in the latter part of the first trimester, including (but not limited to) the absence of formal societal recommendations and lack of payer awareness of the importance of this early examination. Furthermore, it will take additional training of ultrasonographers and ultrasonologists and clinical experience to provide equity in services to all communities and uniform access to the detailed first-trimester ultrasound examination when clinically indicated.

CME FOR THE CLINICAL EXPERT SERIES Learning Objectives for “First-Trimester Ultrasound Screening in Routine Obstetric Practice”

After completing this continuing education activity, you will be able to:

List the prevalence and clinical significance of structural and chromosomal abnormalities; Outline the advantages of performing routine ultrasonographic evaluations of the fetus at the end of the first trimester; Discuss the false-positive and false-negative rates of first-trimester ultrasound examinations and their effects on clinical counseling; and Implement patterns of practice to optimize the use of first-trimester ultrasonography. Instructions for Obtaining AMA PRA Category 1 Credits™ Continuing Medical Education credit is provided through joint providership with The American College of Obstetricians and Gynecologists.

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