TWO DIMENSIONAL ULTRASONOGRAPHY AT 14 -16 WEEKS OF GESTATION FOR DETECTION OF FETAL STRUCTURAL ANOMALIES

TWO DIMENSIONAL ULTRASONOGRAPHY AT 14 -16 WEEKS OF GESTATION FOR DETECTION OF FETAL STRUCTURAL ANOMALIES

By

Amr Abo-Zaid Youssef, Mohamed Taher Ismail, Mohammad Salah El-Din Hassanin and Mohamed Kamal Etman

Department of Obstetrics and Gynecology, Faculty of Medicine, Al Azhar University

Corresponding author: Amr Abo-Zaid Youssef, E-mail: siramro@yahoo.com

ABSTRACT

Background: Congenital anomalies occur in 2-3% of all births. This is an important cause of perinatal morbidity and mortality and account for 20-30% of perinatal death. The antenatal detection of fetal malformation by early ultrasound screening has been shown to reduce perinatal mortality by allowing elective termination of malformed fetuses.

Objective: To compare early targeted organ scanning at gestational ages ranging from 14-16 weeks versus 18-22 weeks.

Patients and methods: This prospective observational study was performed at Ultrasound special care unit for the fetus, Ain Shams Maternity Hospital, from January 2016 till December 2019, after obtaining approval from the local ethics committee. One hundred and fifty pregnant women were scanned twice for targeted detailed organ scanning once at 14-16 weeks, then rescanned again at 18-22 weeks.

Results: The early-second trimester detailed anatomy scan was significantly less accurate than that of the mid-trimester as regards the heart details. The four chamber view of the heart was well seen at 18-22 weeks in 144 pregnant women (96%) but was only seen at 14-16 weeks in 127 pregnant women (84.7%). The great vessels outflow tracts were better seen at 18-22 weeks in 141 pregnant women (94%), and only seen in 119 pregnant women (79.3%) at 14-16 weeks. Moreover, the kidneys were well visualized at 18-22 weeks in 144 pregnant women (96.0%), and only visualized in 127 pregnant women (84.7%) at 14-16 weeks. There was a significant difference between the two periods regarding all parameters in head, face, the umbilical cord and the external genitalia.

Conclusion: None of both gestational ages (14-16 weeks and 18-22 weeks) were clearly superior to the other.

Keywords: Fetal structural anomalies, Two-dimensional ultrasonography, Early second trimester screening, Obstetric ultrasound, Targeted organ scanning.

INTRODUCTION

     In general, screening for fetal structural and chromosomal abnormalities is a crucial part of antenatal care. The main purpose of a fetal ultrasound scan is to provide a precise information that simplify the delivery of enhanced antenatal care with the best possible outcomes for both the mother and fetus (Salomon et al., 2011).

     Congenital anomalies occur in 2-3% of all births. They are an important cause of perinatal morbidity, and mortality and account for 20-30% of perinatal death. Survivors have mental and physical disability. The psychological trauma and cost associated with fetal abnormalities have led to the use of ultrasound for the prenatal diagnosis as an essential part of antenatal care (Mathews and Mac Dorman, 2012).

     Timor-Tritsch et al. (2010) cited that ultrasound examination, with state-of-the-art equipment and in expert hands, can visualize as many structures at 13-14 weeks as it could at 16 weeks 5-10 years previously and at 20-22 weeks 15-20 years previously. Towards the end of the first trimester, the scan additionally offers an opportunity to identify gross fetal irregularities and in health systems that offer first-trimester aneuploidy screening, the measuring of the nuchal translucency thickness (NT) is also available.

     After about 18 weeks, fetal anatomy is evaluated thoroughly through ultrasound. It is essential to use methodical routine in the implementation and assessment of anatomic evaluation of high-risk pregnancies (Hurt et al., 2016).

     The aim of this work was to evaluate the potentials of the scanning at 14-16 weeks, using two-dimensional trans-abdominal ultrasound, in high risk population group, concerning the precision in visualizing fetal organs at that age, and the accuracy in the diagnosis of fetal anomalies when compared with the mid-trimester ultrasound fetal anatomy scan.

PATIENTS AND METHODS

     This prospective observational, study was performed at Ultrasound special care unit for the fetus, Ain Shams Maternity Hospital, from January 2016 till December 2019, after obtaining approval from the local ethics committee. One hundred and fifty pregnant women were scanned twice for targeted detailed organ scanning once at 14-16 weeks then rescanned again at 18-22 weeks.

Ethical Aspects: All participating women signed informed verbal consents before being recruited in the study after through explanation of the procedure and purpose of the study.

Inclusion criteria: Study was carried out on pregnant women of high-risk pregnancy as they visited the ultrasound unit for their antenatal care with the following criteria:

1.  Gestational age (14 weeks to 16 weeks) for the early scan and (18 weeks to 22 weeks) for the late scan.

2.  High risk pregnant women included one or more of the following criteria:

•   Positive family or personal history of congenital abnormalities.

•   Maternal age above 35 years.

•   Positive consanguinity.

•   Bad obstetric history as previous IUFD, recurrent pregnancy loss.

•   Maternal disease, history of drug intake or radiation exposure.

Intervention:

The recruited patients were subjected to the following:

1.  Detailed history:

A. Personal history: Name, age, occupation, residence, consanguinity and special habits of medical importance.

B. Obstetric history: First day of last menstrual period for accurate estimation of gestational age.

C. Past history: History of any medical disorder, bad obstetric history as previous IUFD, recurrent pregnancy loss.

D. History of the present pregnancy:

-   Medical condition to define high risk pregnancy.

-   History of drug intake or radiation exposure in the first trimester.

2.         Transabdominal Ultrasound scans to determine fetal gestational age and any existing fetal anomaly through measuring the biparietal diameter, abdominal circumference, femur length and detailed cardiac scan.

Follow up:

Each pregnant woman was scheduled for two ultrasound examinations:

1.  First ultrasound was done at the time of booking (14-16 weeks).

2.  A second examination was scheduled at mid trimester between 18-22 weeks.

3.  All ultrasonographic examinations were performed using the same ultrasound device, which will be Voluson E6 BT 12 (GE) with a convex abdominal probe RAB 6D-4D curved array at The Special Care Center for Fetus Unit at Ain Shams University Maternity Hospital.

Sample size calculation: Based on the results published by Ebrashy et al. (2010), Alpha error = 5% (two-sided), power of the study = 80%, ability of 2D ultrasonography to visualize cranium abnormality = 85%, ability of 2D ultrasonography to visualize complete fetal abnormality = 63%, and estimated required sample sizes: N =150 pregnant women.

Statistical methods:

     All statistical calculations were done using computer program SPSS (Statistical Package for the Social Sciences; SPSS Inc., Chicago, IL, USA) release 15 for Microsoft Windows. Continuous data were presented as range, mean and standard deviation categorical data were presented as number and percentage and were comqunce by chi-square test. Significance level was set at 0.05.

RESULTS

     Maternal demographic data showed that the mean (+SD) of age was 31.5 ± 6.344288 years, Percentage of consanguinity was 14.0%, percentage of PG is 12.0%, P1 was 20.0%, P2 was 32.0%, and P3 or more was 36.0%, percentage of pregnant women with positive past history was 34.0%, percentage of those with positive family history was 9.0%, and percentage of those with positive present history was 32.0% (Table 1).

Table (1):  Maternal background parameters (maternal demographic data)

     The current study showed that there was a statistically significant difference between the two periods regarding all parameters in head. The intact cranium, midline falx and thalami were detected at 14 -16 weeks more than 18 – 22 weeks while cavum septi pellucidi, cerebral ventricles, cerebellum and cisterna magna were detected at 18 – 22 weeks more than 14 – 16 weeks. There was a statistically significant difference between the two periods regarding all parameters in face.

There was no statistically significant difference found between patients at 14 - 16 weeks and at 18 – 22 weeks regarding stomach in normal position and bowel not dilated, while the presence of both kidneys was seen in 78 patients (52.0%) at the period of 14 - 16 weeks and seen in 144 patients (96.0%) at the period of 18-22 weeks which was highly statistically significant difference between the two periods with p-value < 0.001.

     The study showed that no statistically significant difference between the two periods regarding all skeletal parameters and all placental parameters. Regarding the umbilical cord and the external genitalia, there was a statistically significant difference between the two periods.

     There was a statistically significant difference between the two periods regarding the umbilical cord, but no statistically significant difference between the two periods regarding the external genitalia (Table 2).

Table (2):  Comparison between patients at 14 – 16 weeks and at 18 – 22 weeks regarding head details, face, abdominal details, skeletal details, placenta, umbilical cord and genitalia

DISCUSSION

     This study showed that the mean (+SD) of age was 31.5 ± 6.344288 years. As regards consanguinity 14.0% have positive consanguinity and 86% have negative consanguinity and as regards parity 12.0% were PG, 20.0% were P1, 32.0% were P2 and 36.0% were P3 or more.

     In the current study, the early-second trimester detailed anatomy scan was significantly less accurate than that of the mid-trimester. As regards the heart details, the four chamber view of the heart were well seen at 18-22 weeks in 144 pregnant women (96%), but was only seen at 14-16 weeks in 127 pregnant women (84.7%). The great vessels outflow tracts were better seen at 18-22 weeks in 141 pregnant women (94%), and was only seen in 119 pregnant women (79.3%) at 14-16 weeks. Moreover, the kidneys were well visualized at 18-22 weeks in 144 pregnant women (96.0%) and only visualized in 127 pregnant women (84.7%) at 14-16 weeks.

     This was supported by Yagel et al. (2015) who stated that the second trimester detailed anatomy scan was markedly better than in the first and early-second in terms of organs and systems visualization. This was also agreed by Ebrashy et al. (2010) in a 5-year period prospective study.

     The results of the current study regarding the heart details were the same as Allan (2010) who concluded that adequate views of the heart, to include the four-chamber view and the great arteries, can be obtained in the majority of patients by most ultra-sonographers at around 20 weeks of gestation.

     On the other hand, Becker and Wegner (2010) conducted a prospective study and concluded that an anomaly scan at 11–13 gestational weeks by expert operators provides the chance of detecting the majority of fetal anomalies around the transition from the first to the second trimester.

    O ur study showed that detailed anatomy scan of the fetus at 14-16 weeks has no statistically significant difference in comparison with scan of the fetus at 18-22 weeks regarding head details including (Intact cranium, Midline falx and Thalami), neck details including (Absence of cystic Hygroma and Nuchal fold thickness), heart and chest including (Presence of heart activity and Absence of diaphragmatic hernia), abdomen including (Stomach in normal position and Bowel not dilated), all spine and skeletal details, placenta and fetal genitalia, but current study showed that detailed anatomy scan of the fetus at 14-16 weeks has a statistically significant difference in comparison with scan of the fetus at 18-22 weeks regarding in head details including (Cavum septi pellucidi, Cerebral ventricles, Cerebellum and Cisterna magna), face details including (Both orbits present, Mouth present and upper lip intact), heart and chest including (four chamber view and aortic and pulmonary outflow tracts), abdomen including (presence of both kidneys) and umbilical cord vessels.

     The current study concluded that detailed transabdominal fetal anatomy scan at 14-16 weeks versus 18-22 weeks was statistically insignificant in most fetal details’ parameters, but none of the two periods has an advantage over the other as both are of same importance.

     That agreed by Westin et al. (2010) who conducted a randomized controlled study to compare the antenatal detection rate of malformations in chromosomally normal fetuses between a strategy of offering one routine ultrasound examination at 12 gestational weeks and a strategy of offering one routine examination at 18 gestational weeks concluded that none of the two strategies for prenatal diagnosis is clearly superior to the other. The 12-week strategy has the advantage that most lethal malformations were detected at <15 gestational weeks, enabling earlier pregnancy termination. The 18-week strategy seems to be associated with a slightly higher detection rate of major malformations, although the difference was not statistically significant.

     The points of strength in this study, that all patients were examined by the same examiner, same ultrasound machine and results were evaluated with those recorded during the study and this was attended by candidate of study all high-risk pregnancy cases.

CONCLUSION

     None of both gestational ages (14-16 weeks and 18-22) was clearly superior to the other. As at 14-16 weeks has the advantage that most lethal malformations are detected early in pregnancy allowing early termination and at 18-22 weeks is associated with a slightly higher detection rate of major malformations.

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