First trimester ultrasonographic diagnosis of fetal structural abnormalities in a low risk population.

OBJECTIVES: Ultrasonographic screening between 12(+0) and 13(+6) weeks for fetal structural abnormalities using transabdominal sonography and, where necessary, transvaginal sonography in a low risk population. DESIGN: A prospective observational study. SETTING: London teaching hospital. METHODS: Pregnant women with a total of 1632 low risk viable fetuses between 12(+0) and 13(+6) weeks of gestation were scanned using transabdominal and, where necessary, transvaginal sonography (40%). If the anatomical survey was normal, the women underwent routine 18-20 week anomaly scans. Pregnancy outcomes were obtained from radiological and neonatal computerised databases, and postal or telephone patient enquiry. RESULTS: Seventeen (1.0%) major structural abnormalities were diagnosed in the study group. Of these, 11 (64.7%) were diagnosed at the 12-13 week scan, three diagnosed in the mid-trimester and three postnatally. Of the fetal abnormalities diagnosed antenatally, 78.6% were diagnosed in the first trimester. The sensitivity of abnormality detection by the combination of both first and second trimester scans was 82.3%. In addition, a significant number of missed abortions (n = 36) were also diagnosed by the first trimester scan. CONCLUSION: This study has demonstrated the potential of screening a low risk population for fetal abnormalities at 12-13 weeks of gestation using transabdominal sonography and, where necessary, transvaginal sonography. Larger studies are required to establish the clinical value of the first trimester scan.

Prenatal diagnosis of trisomy 21 in monozygotic twins with increased nuchal translucency and abnormal serum biochemistry.

We present a case of a monozygotic twin pregnancy who underwent routine screening for chromosomal abnormalities at 14 weeks of gestation by ultrasonographic measurement of nuchal translucency and biochemical analysis of maternal serum alpha fetoprotein and free beta human chorionic gonadotrophin levels. Both screening methods indicated the pregnancy to be at increased risk of Down syndrome, with the ultrasound findings suggesting both fetuses to be affected. An amniocentesis was performed, and karyotype analysis revealed trisomy 21 in both fetuses; the mother subsequently opted for a termination of pregnancy. This case illustrates that screening for trisomy 21 in twin pregnancies is possible by both nuchal translucency measurement and maternal serum markers.

Acceptability by patients of transvaginal sonography in the elective assessment of the first-trimester fetus.

The acceptability of transvaginal sonography (TVS) for visualization of first-trimester fetal anatomy was investigated in 160 women sequentially attending a routine dating scan clinic at 12-13 weeks' gestation. All women underwent transabdominal sonography (TAS) in the first instance to assess gestational age. Of these women, 88.1% agreed to undergo TVS. The main reasons for declining were fear of miscarriage (42.1%) and discomfort (36.8%). With TVS, 51.8% described no discomfort, 47.5% mild and 0.7% marked discomfort. Of the women who underwent TVS, 95% said that they would have no concerns about a further TVS in another pregnancy. Of those women who had previously had TVS (11.9%), all agreed to have TVS in this pregnancy and experienced significantly less concern about the procedure than did those who had never had TVS before. TAS was associated with discomfort and inconvenience only if women tried to fill their bladder prior to the scan. In conclusion, TVS is acceptable and well tolerated by an unselected pregnant population. Acceptability rates for TVS should improve as its use becomes more widespread.

Nuchal translucency measurements: frequency distribution and changes with gestation in a general population.

OBJECTIVE: To investigate nuchal translucency variation with crown-rump length (CRL) in the first trimester in normal fetuses. DESIGN: A prospective observational study. SETTING: Department of obstetrics in a London teaching hospital. PARTICIPANTS: One thousand seven hundred and seven pregnant women (1685 singleton and 22 twin pregnancies) with chromosomally normal fetuses between 9+zero and 14+6 weeks of gestation were recruited sequentially from a dating scan clinic. Nuchal translucency was measured in 94.9% by transabdominal sonography (TAS) and by transvaginal sonography (TVS) if difficulty was encountered with TAS (5.1%). Nuchal translucency measurement was repeated in 136 fetuses: the first scan between between 9+zero-11+6 weeks and the second over 12 weeks of gestation. RESULTS: Of this general population, 4.2% had a nuchal translucency (NT) measurement > or = 2.5 mm, but this proportion varied significantly between gestational age groups (P = 0.011). The repeatability coefficients for NT measurements were 0.44 mm and 0.23 mm for TAS and TVS, respectively. The cross-sectional data demonstrate an increase in nuchal translucency measurement between 9 and 12 weeks of gestation and then a decrease at 13-14 weeks. This relation is best modelled using the quadratic equation: log10 (NT) = -1.03 + (0.0314 x CRL) - (2.20 x 10(-4) x CRL2). Longitudinal data confirmed an increase of nuchal translucency measurements with increasing gestation. CONCLUSION: Nuchal translucency measurements increase significantly with increasing gestation. The use of a single threshold nuchal translucency measurement throughout the first trimester is inappropriate. We propose reference ranges of nuchal translucency measurements with gestation, aiming to improve the performance of nuchal translucency screening for chromosomal abnormalities.

Nuchal translucency measurement: training of potential examiners.

The aim of this study was to assess a training regimen for nuchal translucency measurement by transabdominal (TAS) and transvaginal sonography (TVS). After initial instruction regarding the criteria for correct nuchal translucency measurement, trainees (A and B) and an experienced examiner (C) performed nuchal translucency measurements on fetuses of 10-13 weeks' gestation, and the trainees' ability to obtain a measurement, repeatability and levels of agreement were assessed. In addition, a further experienced examiner (D) performed nuchal translucency measurements to validate the training regimen. Examiner C obtained nuchal translucency measurements in 94% by TAS, 93% by TVS and 100% by a combination of both scan modes. The repeatability coefficient was 0.40 mm and 0.24 mm for TAS and TVS, respectively. Trainees A and B were considered trained after 80 and 100 scans with TAS and TVS, respectively. They were considered trained when they could consistently obtain measurements that were of comparable repeatability and comparable levels of agreement with those of examiner C. The trainees' difficulties with TAS were in achieving satisfactory repeatability and levels of agreement, but with TVS it was ability in obtaining a measurement. We propose the training methods, standards and criteria used in this study as the basis for training sonographers in nuchal translucency measurements.

First-trimester diagnosis of Meckel-Gruber syndrome by transabdominal sonography in a low-risk case.

Meckel-Gruber syndrome is a rare autosomal recessive disorder often resulting in neonatal death within a few hours of life. The condition is usually diagnosed ultrasonographically in the second trimester and earlier diagnosis has been mainly confined to high recurrence risk pregnancies. We describe the earliest non-invasive diagnosis of this condition at 12+2 weeks' gestation in a patient with no previous history using transabdominal ultrasound. Pregnancy termination was declined. Subsequent development of anhydramnios in the mid-trimester resulted in poor fetal visualization. We propose that first-trimester diagnosis of this condition is not only possible but preferable, as normal liquor volume facilitates visualization of fetal anatomy.

The measurement of nuchal translucency with transabdominal and transvaginal sonography--success rates, repeatability and levels of agreement.

The objective of this prospective observational study was to assess the abilities of transabdominal sonography (TAS) and transvaginal sonography (TVS) to measure nuchal translucency (NT) and to establish the levels of agreement between the two scan mode measures. The study was carried out in the Fetal Medicine Unit and 242 pregnant women were recruited from a routine dating scan clinic. All patients underwent TAS and TVS, and two separately obtained measurements of the NT were recorded. The ability to measure NT and the repeatability and levels of agreement between the scan mode measures was assessed. A measurement of NT was obtained in 92% and 90% of fetuses using TAS and TVS, respectively, and in 100% of fetuses by combination of the scan modes. Failure to measure NT with TAS was due to inability to obtain mid-sagittal views because of unfavourable fetal lie or poor resolution, especially in patients with high body mass indexes. Although there was generally good correlation between the two scan mode measurements, a significant overmeasuring of NT was observed with TAS (mean difference +/- SD: 0.10 +/- 0.29 mm, p < 0.01). The repeatability coefficients were 0.40 mm and 0.22 mm for TAS and TVS, respectively. An examiner needs to have the ability and equipment to perform TAS and TVS to consistently measure NT. Considering the overmeasurement of NT with TAS and the improved repeatability with TVS, measurements of NT in a screening programme for chromosomal abnormalities should be by TVS, at least when a prior TAS reveals a value close to a threshold level.