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Keywords:

  • fetal abnormalities;
  • fetal anatomy;
  • first trimester;
  • nuchal translucency

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

Objective

To assess the feasibility of examining cardiac and non-cardiac fetal anatomy in a low-risk population in the setting of the routine 11–14-week ultrasound scan.

Methods

This was a prospective study of 1144 women with viable, singleton pregnancies at 11–14 weeks of gestation. The ultrasound examination was performed transabdominally and transvaginally and fetal anatomy assessment included visualization of the skull, brain, face, spine, four-chamber and three-vessel views of the heart, stomach, abdominal wall, kidneys, bladder and extremities.

Results

Complete examination of the fetal anatomy was achieved in 48% of the fetuses, whereas non-cardiac anatomy was examined successfully in 86% of the fetuses. The use of the transvaginal approach increased successful examination of the fetal anatomy from 72% to 86% of the fetuses and transvaginal scanning was particularly helpful in examining the face, kidneys and bladder. Non-cardiac anatomy visualization increased from 65% for fetuses with a crown–rump length of 45–54 mm, to 84%, 93% and 96% for fetuses with a crown–rump length of 55–64 mm, 65–74 mm and more than 74 mm, respectively. In the same groups the four-chamber view was seen in 67%, 86%, 93% and 97% of fetuses, and the three-vessel view was seen in 25%, 46%, 58% and 67% of fetuses, respectively. Maternal habitus and crown–rump length were found to be statistically significant contributors to the rate of successful examination of fetal anatomy.

Conclusion

Examination of fetal anatomy is feasible during the routine 11–14-week scan. The optimal gestational age for examining both cardiac and non-cardiac anatomy is from the beginning of the 12th week to the end of the 13th week of gestation. Access to the transvaginal approach is important for completeness of the examination. Copyright © 2004 ISUOG. Published by John Wiley & Sons, Ltd.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

Ultrasound examination at 11–14 weeks of gestation aims to confirm the gestational age, assess chorionicity in multiple pregnancies, measure the nuchal translucency thickness and visualize the basic anatomical structures of the fetus. Nuchal translucency measurement has been established as the best imaging method of assessing the risk of chromosomal abnormality, thus making the 11–14-week scan the first detailed ultrasound examination of the fetus1.

At the beginning of the 1990s a number of studies used transvaginal ultrasound to describe in great detail the evolving anatomy of the embryo and fetus2–9. However, although in the general population structural defects are relatively common (3–5%), and of these, cardiac defects are the most common, few studies have addressed the issue of examining fetal anatomy in low-risk populations as part of the 11–14-week scan10–16. Visualization of the cardiac anatomy at this gestational period has been reported from specialists in fetal echocardiography and has been limited mainly to high-risk pregnancies17–27.

Our study assessed the feasibility of examining cardiac and non-cardiac anatomy in a low-risk population in the setting of the routine 11–14-week ultrasound scan.

Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

Screening for chromosomal abnormalities by nuchal translucency measurement and maternal serum biochemistry (free beta-human chorionic gonadotropin (β-hCG) and pregnancy-associated plasma protein-A (PAPP-A)) has been offered by the fetal medicine unit of Alexandra Maternity Hospital to all pregnant women booking for delivery since May 2002. Between then and December 2003, 1144 pregnant women with viable singleton pregnancies opted to participate in the study after full counseling. They all gave written informed consent.

Ultrasound examinations were performed at the 11–14-week period according to the guidelines of The Fetal Medicine Foundation, London (http://www.fetalmedicine.com)1. Gestational age was calculated from the last menstrual period. In women with unknown dates or when there was a difference greater than 7 days between menstrual age and ultrasound age, the pregnancy was dated by crown–rump length (CRL).

Ultrasound examinations were performed both transabdominally and transvaginally using an ATL Ultramark 9 (USA) ultrasound machine equipped with a 5-MHz curvilinear transducer and a 9-MHz vaginal transducer. Ultrasound examinations were performed by five operators: one operator experienced in first-trimester scanning who trained and supervised four research fellows. Thirty-minute appointment slots were allocated for each patient.

Fetal anatomy was examined as follows:

  • 1.
    Skull and brain: examination of the completeness of the skull, the presence of the falx and the butterfly shape of the choroid plexuses.
  • 2.
    Face: examination of the orbits and lenses and the view of the fetal profile.
  • 3.
    Spine: examination of the alignment of the vertebrae and the skin covering the spine from the cervical to the sacral region.
  • 4.
    Heart: examination of the four-chamber view (visualization of the two atria and ventricles, the crux and the atrioventricular valves) and the three-vessel view of the great vessels (visualization of the cross-sectional view of the pulmonary artery, aorta and superior vena cava (Figures 1 and 2).
  • 5.
    Stomach: visualization of the stomach as a hypoechoic structure in the left upper abdomen.
  • 6.
    Abdomen: examination of the abdominal wall and the umbilical cord insertion.
  • 7.
    Kidneys: visualization of the kidneys as hyperechoic structures with a hypoechoic center lateral to the spine.
  • 8.
    Bladder: visualization of the bladder as a hypoechoic structure in the fetal pelvis.
  • 9.
    Extremities: examination of the long bones, fingers, toes and the movement and posture of the joints.
thumbnail image

Figure 1. Ultrasound image showing the four-chamber view of a 13-week fetus.

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Figure 2. Ultrasound image showing the three-vessel view of a 13-week fetus.

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The StatsDirect statistical software version 1.9.15 was used for statistical analysis. Logistic regression was used to examine the contribution of maternal age, race, body mass index (BMI), smoking, history of laparotomy, bleeding during pregnancy and CRL in successful visualization of fetal anatomy.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

A total of 1144 pregnant women with viable singleton pregnancies participated in the study. The mothers were 15–48 (median, 29) years old, 457 (39.94%) were primigravid, the majority were Caucasian (1131, 98.86%) and 170 women (14.86%) reported smoking during pregnancy. In 11 cases there was a family and/or previous pregnancy history of structural anomalies (0.96%). Conception was achieved with the use of assisted reproduction techniques in 18 cases (1.57%). Ultrasound examinations were performed from the beginning of the 11th to the end of the 13th gestational week, corresponding to a fetal CRL of 45–84 (median, 64.9) mm. Fetuses were divided into four groups according to CRL: Group 1 included fetuses with a CRL of 45–54 mm (11 + 0 to 11 + 6 weeks); Group 2 was fetuses with a CRL of 55–64 mm (12 + 0 to 12 + 5 weeks); Group 3 was fetuses with a CRL of 65–74 mm (12 + 6 to 13 + 3 weeks); Group 4 was fetuses with a CRL bigger than 74 mm (13 + 4 to 14 + 0 weeks).

Using a combination of the transabdominal and transvaginal routes, a full examination of the fetal anatomy according to our protocol was achieved in 48% of the fetuses, while all anatomical structures except the fetal heart were succesfully visualized in 86% of the fetuses. Table 1 shows the percentages of successful visualization of the fetal organs according to CRL. Cardiac anatomy was seen in 50% of fetuses, with visualization of the four-chamber view in 87% of cases and of the three-vessel view in 50% of cases. Table 2 shows the percentages of successful visualization of the four-chamber view and the three-vessel view of the fetal heart according to CRL.

Table 1. Visualization of fetal anatomical structures according to crown–rump length (CRL)
CRL (mm)nSuccessful visualization (n (%))
Anatomy check IAnatomy check IIHead/brainFaceSpineHeartAbdomenStomachKidneysBladderExtremities
  1. Anatomy check I, includes all organs except the heart; Anatomy check II, all organs including the heart.

45–54 174113 (64.94)38 (21.83)174 (100)171 (98.27)172 (98.85)44 (25.28)172 (98.85)166 (95.40)123 (70.68)170 (97.70)174 (100)
55–64 400337 (84.25)173 (43.25)400 (100)398 (99.5)399 (99.75)183 (45.75)400 (100)398 (99.50)341 (85.25)397 (99.25)400 (100)
65–74 413386 (93.46)233 (56.41)413 (100)409 (99.03)413 (100)238 (57.62)413 (100)412 (99.75)388 (93.94)412 (99.75)413 (100)
75–82 157150 (95.54)105 (66.87)157 (100)157 (100)157 (100)105 (66.87)157 (100)157 (100)150 (95.54)157 (100)157 (100)
Total1144986 (86.18)549 (47.98)1144 (100)1135 (99.21)1141 (99.73)570 (49.82)1142 (99.82)1133 (99.03)1002 (87.58)1136 (99.30)1144 (100)
Table 2. Visualization of the four-chamber view and the three-vessel view of the fetal heart according to crown–rump length
CRL (mm)nSuccessful visualization (n (%))
HeartFour-chamber viewThree-vessel view
45–54 17444 (25.28)117 (67.24)44 (25.28)
55–64 400183 (45.75)344 (86)184 (46)
65–74 413238 (57.62)386 (93.46)238 (57.62)
75–82 157105 (66.87)153 (97.45)105 (66.87)
Total1144570 (49.82)1000 (87.41)571 (49.91)

The use of the transvaginal approach increased successful examination of the fetal anatomy from 72% to 86% of the fetuses. Table 3 shows the contribution of transvaginal scanning in visualizing fetal anatomy according to CRL. Table 4 shows the contribution of transvaginal scanning in the examination of the fetal organs and Table 5 shows its contribution in the examination of the fetal heart.

Table 3. The contribution of transvaginal scanning in visualizing fetal anatomy according to crown–rump length
CRL (mm)nSuccessful visualization (n (%))
Transabdominal scanTransabdominal & transvaginal scan
45–54 17499 (56.89)113 (64.94)
55–64 400301 (75.25)337 (84.25)
65–74 413307 (74.33)386 (93.46)
75–82 157119 (75.79)150 (95.54)
Total1144826 (72.20)986 (86.18)
Table 4. The contribution of transvaginal scanning in visualizing fetal organs at 11–14 weeks (n = 1144)
OrganSuccessful visualization (n (%))
Transabdominal scanTransabdominal & transvaginal scan
Head/Brain1123 (98.16)1144 (100)
Face1049 (91.69)1135 (99.21)
Spine1111 (97.11)1141 (99.73)
Abdomen1108 (96.85)1142 (99.82)
Stomach1099 (96.06)1133 (99.03)
Kidneys892 (77.97)1002 (87.58)
Bladder1035 (90.47)1136 (99.30)
Extremities1126 (98.42%)1144 (100%)
Table 5. The contribution of transvaginal scanning in visualizing the fetal heart according to crown–rump length
CRL (mm)nSuccessful visualization (n (%))
Transabdominal scanTransabdominal & transvaginal scan
45–54 17443 (24.71)44 (25.28)
55–64 400176 (44.0)183 (45.75)
65–74 413208 (50.36)238 (57.62)
75–82 15792 (58.59)105 (66.87)
Total1144519 (45.36)570 (49.82)

Only BMI and CRL were found to be statistically significant contributors to the rate of successful examination of fetal anatomy (OR, 0.90 and 95% CI, 0.88–0.93 for BMI; OR, 1.072 and 95% CI, 1.05–1.08 for CRL). There were 94 (8.2%) obese women with a BMI ≥ 30. In this group a full anatomy check was possible in only 26 cases (27.6%), which was significantly less than the visualization rates in the study population (P < 0.0001).

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

Our study showed that detailed examination of the fetal organs is feasible in the routine 11–14-week scan. Non-cardiac anatomical visualization increased with increasing CRL. Overall, non-cardiac anatomical structures were examined successfully in 86% of the fetuses. The organs other than the heart were visualized in more than 95% of fetuses with the exception of the kidneys (88%). The addition of transvaginal scanning increased visualization rates and this benefit was demonstrated in all gestational groups. Transvaginal scanning was particularly helpful in examining the face, kidneys and bladder.

In a screening study for structural abnormalities at 11–14 weeks using transvaginal ultrasound, fetal anatomy (not including face and heart) was seen in 94% of the cases11. Similar results were reported by Braithwaite et al. in an anatomical survey of 298 fetuses at 12 + 0 to 13 + 6 weeks of gestation13. They were able to complete the examination of the fetal anatomy, including the four-chamber view, in 95% of the fetuses, in accordance with our figures at the same gestational age.

The four-chamber view and three-vessel view were visible in 87% and 50% of cases, respectively. Visualization rates increased with increasing CRL. For the four-chamber and three-vessel views the addition of transvaginal scanning increased successful examination rates by about 5% and this effect was mainly seen in fetuses greater than 65 mm, probably representing cases where the examination of the fetal heart was hindered by fetal position.

Visualization rates reported in the literature for the four-chamber view vary from 17% to 88% in the 11th week, 36% to 97% in the 12th week and 74% to 100% in the 13th week17–21, 23. Similarly, visualization rates for the outflow tracts vary between 0% and 75% during the 11th week, 40% and 93% during the 12th week and 38% and 100% during the 13th week of pregnancy17–21, 23. Successful examination of the fetal heart including both four-chamber view and outflow tracts has been shown to increase from 0–75% in the 11th week to 31–93% in the 12th week and 43–100% in the 13th week, with the higher percentages being reported in more recent studies19, 21, 23, 26.

Our study showed that examination of the fetal anatomy is feasible during the routine 11–14-week scan, the completeness of the examination depending mainly on maternal habitus and gestational age. In accordance with other authors we found the optimal gestational age for examining both cardiac and non-cardiac anatomy to be from the beginning of the 12th week to the end of the 13th week of gestation13, 26. Access to the transvaginal approach was important in completing the examination.

With the modern trend of shifting prenatal diagnosis to the earliest possible gestational age and with advancing technology, it is not difficult to see the 11–14-week scan as becoming the first anomaly scan with the aim of diagnosing the severest structural anomalies, thus giving the parents earlier reassurance about the well-being of their fetus.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References