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Short fetal nasal bone predicts increased likelihood of Down syndrome
Monday, 29 November 1999 19:00 | 
| Specialties - Obstetrics and Gynaecology |
New study results confirm that documenting total absence of a nasal bone on a fetus during the second trimester can identify nearly half of all fetuses affected by Down syndrome.
New study results confirm that documenting total absence of a nasal bone on a fetus during the second trimester can identify nearly half of all fetuses affected by Down syndrome, investigators report in the February issue of Obstetrics and Gynecology. The research team also reports that hypoplasia of the nasal bone is also a predictor of trisomy 21.
Dr. Carolyn M. Zelop, at St. Francis Hospital in Hartford, Connecticut, and her associates first conducted a retrospective analysis to establish the expected normal distribution of fetal nasal bone length, using ultrasound records of 732 pregnancies during the second trimester. They excluded pregnancies affected with Down syndrome or other significant chromosome abnormalities.
Nasal bone lengths were converted to "multiples of the median" (MoM) with adjustment for maternal race and ethnicity and week of gestation. They then converted nasal bone length of the 10 fetuses with Down syndrome into race or ethnicity-adjusted MoM using the same method.
To confirm their analysis, they prospectively evaluated 1,794 women referred for second-trimester ultrasound, with nasal bone measurements converted to MoM based on the formula established in the first cohort. Results indicated that 11 fetuses had Down syndrome.
With the two cohorts combined, nasal bone absence had a sensitivity of 47.6 per cent and specificity of 100 per cent.
When they used a cutoff of 0.80 MoM, sensitivity and specificity were 95.2 and 92.7 per cent, respectively. Corresponding values when they used a cutoff of less than 0.75 MoM were 85.7 and 97.1 per cent.
Dr. Zelop and her colleagues do not advocate using nasal bone length to predict an individual patient's risk. "However, we do suggest that careful second-trimester scanning of the midsagittal plane of the fetal facial profile specifically looking for presence or absence of a nasal bone be carried out," they write.
Dr. Joshua A. Copel, an obstetrician at Yale School of Medicine in New Haven, Connecticut, and president-elect of the American Institute of Ultrasound in Medicine, told Reuters Health that "it is challenging to make sure that the 'right place' is found for measuring nasal bone length."
Still, he said, "It's a work in progress. We need to find ways of using ultrasound to perform a physical examination of the fetus and identify diagnostic characteristics."
Obstet Gynecol 2007;109:371-375.
Dr. Carolyn M. Zelop, at St. Francis Hospital in Hartford, Connecticut, and her associates first conducted a retrospective analysis to establish the expected normal distribution of fetal nasal bone length, using ultrasound records of 732 pregnancies during the second trimester. They excluded pregnancies affected with Down syndrome or other significant chromosome abnormalities.
Nasal bone lengths were converted to "multiples of the median" (MoM) with adjustment for maternal race and ethnicity and week of gestation. They then converted nasal bone length of the 10 fetuses with Down syndrome into race or ethnicity-adjusted MoM using the same method.
To confirm their analysis, they prospectively evaluated 1,794 women referred for second-trimester ultrasound, with nasal bone measurements converted to MoM based on the formula established in the first cohort. Results indicated that 11 fetuses had Down syndrome.
With the two cohorts combined, nasal bone absence had a sensitivity of 47.6 per cent and specificity of 100 per cent.
When they used a cutoff of 0.80 MoM, sensitivity and specificity were 95.2 and 92.7 per cent, respectively. Corresponding values when they used a cutoff of less than 0.75 MoM were 85.7 and 97.1 per cent.
Dr. Zelop and her colleagues do not advocate using nasal bone length to predict an individual patient's risk. "However, we do suggest that careful second-trimester scanning of the midsagittal plane of the fetal facial profile specifically looking for presence or absence of a nasal bone be carried out," they write.
Dr. Joshua A. Copel, an obstetrician at Yale School of Medicine in New Haven, Connecticut, and president-elect of the American Institute of Ultrasound in Medicine, told Reuters Health that "it is challenging to make sure that the 'right place' is found for measuring nasal bone length."
Still, he said, "It's a work in progress. We need to find ways of using ultrasound to perform a physical examination of the fetus and identify diagnostic characteristics."
Obstet Gynecol 2007;109:371-375.
