RESEARCH ARTICLE | https://doi.org/10.5005/jp-journals-10016-1252 |
Ultrasound Detection of Fetal Structural Anomalies during First Trimester Nuchal Translucency Scan in Conjunction with Traditional 18–22 Weeks Anomaly Scan
1–4Department of Radiodiagnosis, Sri Guru Ram Das Institute of Medical Sciences and Research, Amritsar, Punjab, India
5Department of Obstetrics and Gynaecology, Sri Guru Ram Das Institute of Medical Sciences and Research, Amritsar, Punjab, India
Corresponding Author: Amandeep Singh, Department of Radiodiagnosis, Sri Guru Ram Das Institute of Medical Sciences and Research, Amritsar, Punjab, India, Phone: +91 9872454954; e-mail: dr.amancs@gmail.com
ABSTRACT
Aim and objective: The purpose of this study is to assess the value of performing a detailed examination of the fetus for structural anomalies in a two stage screening process at first trimester nuchal translucency (NT) scan and mid trimester anomaly scan in general population.
Materials and methods: An observational study was conducted on 400 pregnant females referred to Department of Radiodiagnosis and Imaging in our hospital for NT scan at 11–13+6 weeks of gestational age. All women enrolled in the study were again subjected to traditional 18–22 weeks anatomy scan on follow up.
Results: In our study, total 400 pregnant women were enrolled. Overall congenital anomaly prevalence in study population was 6.7%. Out of which 66.6% anomalies were detected in first trimester. While 35.7% of the anomalies were detected in second trimester anomaly scan. Combined use of NT and second trimester scan detected almost all of the congenital anomalies. However, many of the total anomalies among them were detected earlier in first trimester NT scan.
Conclusion: Early scan can be very helpful in early diagnosis of fetal anomalies. But as many abnormalities cannot be evident in early pregnancy due to ongoing fetal development, second trimester anomaly scan should also be performed along with early screening as two stage screening process.
How to cite this article: Singh A, Kaur R, Gupta K, et al. Ultrasound Detection of Fetal Structural Anomalies during First Trimester Nuchal Translucency Scan in Conjunction with Traditional 18–22 Weeks Anomaly Scan. Int J Infertil Fetal Med 2022;13(1):18–22.
Source of support: Nil
Conflict of interest: None
Keywords: Fetal anomalies, First trimester, Nuchal translucency, Ultrasound.
INTRODUCTION
In general population, incidence rate of major congenital abnormalities at birth is 2–3%, yet the reported rate of perinatal deaths due to these anomalies accounts for 20–25% and even higher percentage of perinatal morbidity.1 Ultrasound is the widely used method for screening and diagnosis of congenital structural abnormalities.2
Traditional anomaly scan also known as level II or Targeted Imaging For Fetal Anomalies (TIFFA) scan for detection of structural anomalies has been performed in second trimester of pregnancy at 18–22 weeks of gestation. However, due to improvement in technology, many of structural anomalies can now be detected in first trimester. Early detection of fetal anomalies in prenatal period allows for better perinatal management and providing expectant mothers with options for decision making.
Many recent studies supported the utility of sonographic detection of major fetal structural abnormalities in the first trimester of pregnancy.3,7 However, some anomalies will not be evident until later in the pregnancy due to ongoing fetal anatomical development. Detection rates (DRs) of anomalies vary according to the organ system being examined, equipment settings, and radiologist experience.8
A screening program for structural anomalies based on two ultrasound examinations, at 11–13 and 18–22 weeks, is gaining acceptance owing to the detection of an increasing number of anomalies in the first trimester. The purpose of this study is to assess the value of performing a detailed examination of the fetus for structural anomalies as a part of routine ultrasound scan in a two stage screening process in the general obstetric population.
MATERIALS AND METHODS
An observational study was conducted on 400 pregnant females referred to Department of Radiodiagnosis and Imaging in our hospital for nuchal translucency (NT) scan at 11–13+6 weeks of gestational age, after getting informed consent and approval from Institutional Ethics Committee. Estimated gestational age was calculated based on last menstrual date or previous ultrasound report if periods were irregular or not sure of her last menstrual period. After getting basic history patients were subjected to Transabdominal ultrasound between 11 and 13+6 weeks and if fetal anatomy survey was not possible to be completed by transabdominal Ultrasonography (USG) alone, a transvaginal USG was performed after counselling and getting consent from the patient. All women enrolled in the study were again subjected to traditional 18–22 weeks anatomy scan on follow up using the transabdominal probe using Voluson E8 (BT 12) ultrasound machine with 3.5–5 MHz Trans abdominal transducer. No specific anatomic imaging protocol was followed. Multiple gestations were excluded from the study.
ULTRASOUND EXAMINATION AT 11–13+6 WEEKS/NUCHAL TRANSLUCENCY SCAN
In the first trimester fetus, a thin layer of fluid is seen in the posterior nuchal region. This layer is called the NT, and its thickness can be measured with ultrasonography. An increased NT in the presence of a normal karyotype is associated with an increased frequency of many structural abnormalities as well as a variety of genetic syndromes. Therefore, an increased NT is an indication for detailed anatomic scanning of the fetus.9 NT of more than 95th percentile was considered as cut off for thickened NT.
Nuchal scan was performed transabdominally and whenever necessary transvaginally to assess the risk of major fetal abnormalities by taking into account the scan findings of NT thickness, nasal bone, ductus venosus flow, and tricuspid regurgitation.
A complete study as per the guidelines laid out by American College of Radiology (ACR)/The American Institute of Ultrasound in Medicine (AIUM)/American College of Obstetricians and Gynaecologists (ACOG)/Fetal Medicine foundation/The International Society of Ultrasound in Obstetrics and Gynaecology (ISUOG) was attempted in every case.10,11
TIFFA SCAN
The second trimester TIFFA SCAN also sometimes called the anomaly scan, anatomy scan, or level II ultrasound, is a pregnancy ultrasound typically performed between 18 and 22 weeks of gestational age. These ultrasound scans observe the fetus for soft markers, which are (subtle) anatomical variations or minor, usually transient, structural change that potentially indicate a risk of serious fetal anomaly but which in itself is probably insignificant.
The targeted imaging for fetal anomalies includes three components.
An evaluation of the fetal environment including the placenta, amniotic fluid, umbilical cord, and maternal uterus, cervix and adnexa
Fetal biometry
Detailed anatomical evaluation of the fetus.
The complete study of fetal anatomy per the guidelines laid out by ACR/AIUM/ACOG/ISUOG was attempted in every case.10,11 Follow up of the babies born was done and findings were corroborated.
RESULTS
During the study period, 400 consecutive unselected pregnancies were evaluated. NT scan and evaluation of fetal structural anomalies was done at 11–13+6 weeks of gestational age. Patients were analyzed based on age distribution, NT, and number of anomalies detected. Out of total anomalies in only two anomalies there was family history of similar anomaly. A total of 18 fetuses among 400 had NT above 95th percentile (Fig. 1). Prevalence of anomalies detected in the first trimester were reported to be 4.5%. Nine of the patients terminated their pregnancy owing to lethal anomalies. Hence, second trimester scan could not be performed in these patients. In rest of women follow up, second trimester anomaly scan was performed at 18–22 weeks. Overall congenital anomaly prevalence in study population was 6.7%. Out of which 66.6% anomalies were detected in first trimester. While 35.7% of the anomalies were detected in second trimester anomaly scan. Combine use of NT and second trimester detected almost all of congenital anomalies. However, many of the anomalies were detected earlier in first trimester at NT scan only. No false positive cases were detected in our study. Anomalies that were detected during the first trimester scan and at follow up second trimester screening were presented in Tables 1 and 2 . Number of anomalies detected in the two stage screening process were more as compared to first trimester alone.
| Outcome | No. of patients | % |
|---|---|---|
| Acrania | 2 | 0.25 |
| Anencephaly | 3 | 0.50 |
| Omphalocele | 2 | 0.50 |
| Clubfoot | 1 | 0.25 |
| Absent nasal bone | 2 | 0.50 |
| Megacystitis | 1 | 1.00 |
| Cystic hygroma | 1 | 0.25 |
| Cleft lip and palate | 1 | 0.25 |
| Body stalk deformity | 1 | 0.25 |
| Diaphragmatic hernia | 1 | 0.25 |
| Normal scan | 385 | 95.75 |
| Outcome | No. of patients (391) | % |
|---|---|---|
| Omphalocele | 2 | 0.50 |
| Renal pelviectasis | 2 | 0.25 |
| Cystic hygroma | 1 | 0.25 |
| Cleft lip and palate | 2 | 0.50 |
| VSD | 1 | 0.25 |
| Chiari malformation | 1 | 0.25 |
| Ventriculomegaly | 2 | 0.50 |
| Clubfoot | 3 | 0.75 |
| Multicystic dysplastic kidney | 1 | 0.25 |
| Megacystitis | 1 | 0.25 |
| Normal scan | 374 | 96.25 |
Most of the major and lethal anomalies were detected at the time of first trimester. Rate of detection of cardiac anomalies were low in our study as dedicated echo was not performed. Anomalies detected in first trimester include acrania (Fig. 2), anencephaly (Fig. 3), absent nasal bone (Fig. 1), megacystitis (4 cm) (Fig. 4), diaphragmatic hernia (Fig. 5), clubfoot (Fig. 6), cleft lip and palate, omphalocele (Fig. 7), cystic hygroma, etc. Anomalies that were missed during NT scan includes renal pelviectasis (>4 mm), Chiari malformation (Fig. 8), pulmonary atresia, multicystic dysplastic kidneys, etc.
Fig. 2: Ultrasound image showing absent calvaria and brain parenchyma
Figs 3A and B: (A) Ultrasound grayscale image showing absence of echogenic rim of skull with disorganized brain matter covered by meninges floating in amniotic fluid; (B) 3D ultrasound images showing absence of fetal skull vault with disorganized brain tissue herniating out
Fig. 4: Ultrasound image showing unusually elongated enlarged urinary bladder (4 cm) in fetus reaching up to the diaphragm
Fig. 5: Ultrasound image showing fetal diaphragmatic hernia as fetal stomach and heart are seen at same level with heart displaced toward right side
Fig. 6: TVS ultrasound image showing clubfoot at 12 weeks of gestation
Fig. 7: Ultrasound image in a case of omphalocele showing herniation of bowel through abdominal wall defect
Fig. 8: Ultrasound examination of fetus with Chiari malformation showing banana-shaped appearance of elongated cerebellum
Severe or lethal abnormalities were detected in 55.5% of cases in the first trimester and 11.11% of those detected at follow up. Most of these major chromosomal abnormalities were diagnosed during the first-trimester evaluation. Many mild anomalies with favorable prognosis also detected in first trimester. A total of 18 fetuses (4.5% of the first-trimester study group) presented with NT >95th percentile. In this group of fetuses with increased NT, the prevalence of major anomalies was 7.9% and their first-trimester DR was 94.4%. In the fetuses with normal NT, none of the major anomalies were detected and the first-trimester DR for anomalies were 55.5%. NT was increased in 61.1% of the fetuses with major abnormalities.
We found that many of the major anomalies can be diagnosed in first trimester at time of NT scan. But due to late development of some organs and late onset of some anomalies role mid trimester scan remain undisputed.
DISCUSSION
NT scan was done at 11–13+6 weeks and follow up scan was done at 18–22 weeks of gestational age in the present study. Time period of 11–13+6 weeks was chosen for early detection of abnormalities because in this time period, fetal anatomy was better visualized and NT could be measured at the same time. So no additional scan was required. This was feasible as both time and money were saved. Both major and minor anomalies were included in our study.
Prevalence rate varied from 1.2% to as high as 7% among various studies, likely variation was due to referral population to tertiary care hospital. Studies including only major anomalies reported lower prevalence than studies including both minor and major anomalies. Also studies including only high-risk population reported more anomalies as compared to studies with general population.11 The prevalence of anomalies in our study group was 4.2%. The detected anomalies were acrania, anencephaly, absent nasal bone, clubfoot, diaphragmatic hernia, megacystitis, omphalocele, and cystic hygroma.
In fetuses with increased NT, the first trimester DR for major anomalies, were 96% compared to 66.7% between those with normal NT.12 In our study, anomalies detected in women with increased NT is 94.4% as compared to 55% amongst with normal NT. It was also found anomalies were more common in advanced age-group women.
In our study, 66.6% of the anomalies identified at the time of NT scan which is in concurrence with other studies. Almost half of the malformations in our study were amenable to be diagnosed in first trimester as reported in current literature. These fetuses were having malformations like acrania, anencephaly, and gastroschisis, etc.13
Our study concluded that although higher percentage of abnormalities could be detected by early scan. But role of mid trimester scan is undisputed as some abnormalities could not be detected by early screening owing to late development of some fetal organs which is in concurrence with study conducted by Oztekin et al. The accuracy of early ultrasonography could be compromised by transient findings like midgut herniation, small septal defects, megacystitis, and hydronephrosis which might get resolved during intrauterine life.14
In our study, we found use of transvaginal approach along with transabdominal definitely improved visualization of structures. However, transvaginal approach limits planes of scan and increases the scan time. Use of Transvaginal sonography (TVS) is justified in cases where better visualization is required such as in obese mothers. Similar findings are seen in studies conducted by others.15
Most of the studies preferred extended protocol in which first trimester sonography was followed up by a second anomaly scan. The obvious edge of an extended protocol was that expected women were offered the option of earlier and safer termination of pregnancy for the severe or lethal abnormalities.16 Early ultrasound might be more precise than second trimester ultrasonography for detection of malformations associated with oligohydramnios and anhydramnios which lead to poor visualization at later gestation necessitating amnioinfusion.17
Early detection of fetal anomalies provide opportunity for early intervention and better management to expectant mothers. It will be safer for mothers to terminate the pregnancy in early period in case of lethal anomalies.18 However, the study had some limitations. Genetic testing was not performed in all the cases and follow up or autopsy of terminated fetuses was not done.
CONCLUSION
NT scan along with extended detailed anatomic survey at 11–13+6 weeks can detect substantial amount of the anomalies. Early diagnosis is beneficial for timely management of congenital malformations. Most importantly it helps in earlier and safer termination of pregnancy in case of lethal anomalies. Main limitation of early fetal anomaly scan is that majority of abnormalities are difficult to identify, due to ongoing fetal development and delayed onset of some anomalies. Thus, second trimester anomaly scan should also be performed along with early screening as two stage screening process. Good embryological and sonography knowledge is needed to avoid potential diagnostic pitfalls.
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