ABSTRACT
OBJECTIVES: To investigate the feasibility and reproducibility of measurements of nasal bone length using a three-dimensional (3D) ultrasound in the first trimester. METHODS: In a prospective study, 118 consecutive pregnant women attending for Down syndrome screening at 11-13 + 6 weeks were recruited. They had successful fetal nasal bone measurement by two-dimensional (2D) ultrasound by four operators. Three-dimensional volumes were recorded in the mid-sagittal plane of fetal profile by the fifth operator and examined using multiplanar techniques. Another independent investigator randomly compared his measurements with one of the four operators. RESULTS: In the subsequent 3D examination, the nasal bone length could be examined in 94 cases (79.7%). The mean difference between the 2D and 3D measurements was 0.19 mm [95% confidence interval (CI) 0.08 to 0.31] (P < 0.05). Limits of agreement were -0.73 to 1.11. The mean differences between these two observers were 0.66 mm (95% CI -0.47 to 0.86) (P < 0.05). CONCLUSIONS: There was significant intermethod difference between the results obtained by 2D and 3D, as well as substantial interobserver variation in 3D measurement of fetal nasal bone length in the first trimester. Independent 3D measurement of nasal bone offers no additional advantages over 2D sonography.
Subject(s)
Imaging, Three-Dimensional/methods , Nasal Bone/embryology , Pregnancy Trimester, First , Ultrasonography, Prenatal/methods , Adult , Down Syndrome/diagnosis , Down Syndrome/diagnostic imaging , Female , Humans , Mass Screening/methods , Nasal Bone/diagnostic imaging , Nuchal Translucency Measurement , Observer Variation , Pregnancy , Prospective Studies , Reproducibility of Results , Young AdultABSTRACT
OBJECTIVE: To determine the performance of trained midwives in second trimester ultrasound screening for fetal structural abnormalities in a low-risk population. DESIGN: Retrospective study. SETTING: University Department of Obstetrics and Gynecology. POPULATION: About 13,882 women with singleton pregnancies. METHODS: The findings of routine second trimester anomaly scan performed by midwives were reviewed. Reasons for referral to maternal fetal medicine (MFM) specialists for further assessment were analyzed. MAIN OUTCOME MEASURES: The detection, false positive and false alarm rates for fetal anomalies. RESULTS: One hundred and eighty-nine pregnancies with unknown outcome were excluded from the final analysis. Overall, 617 (4.51%) women were referred to MFM specialists for further assessment, of which 470 (70.2%) were for soft markers alone and 147 (23.8%) for suspected fetal structural abnormalities. In these 13,693 fetuses with known outcome, malformed fetuses were present in 185, a prevalence of 1.35%. Of these, 115 were detected during the second trimester scan and two were detected in the third trimester. The remaining 68 malformed fetuses, most of which had minor anomalies, were identified after birth. The detection rate for a malformed fetus in second trimester scan was 62.2% (115/185) (95% CI 55.2-69.2). There were four cases of false positives and 33 cases of false alarm. CONCLUSIONS: Experienced midwives with proper training can detect the majority of major structural abnormalities. Continuous audit and quality control plays a significant role in optimizing the fetal structural examination.
