Faculty Bibliography

OBJECTIVE: To estimate the accuracy of evaluating nasal bone length, expressed as multiples of the median (MoM), for the detection of Down syndrome in second- trimester fetuses. METHODS: Expected normal median nasal bone measurements were established for an initial cohort of women receiving fetal ultrasound examinations at 15-24 weeks of gestation. Nasal bone lengths were converted to MoM with adjustment for maternal race and ethnicity using whites as the referent group. Nasal bone MoM were compared in euploid and Down syndrome fetuses. The sensitivity and specificity were evaluated in this initial cohort and in a second cohort in which all ultrasound measurements were carried out prospectively. RESULTS: For the combined data set, 10 of 21 affected pregnancies had an absence of the nasal bone (sensitivity 47.6%), but absence was noted in only 1 of 2,515 unaffected pregnancies (false-positive rate 0.04%). Using less than 0.80 MoM as a cutoff, the sensitivity was 20 of 21 (95.2%), and the false-positive rate was 185 of 2,515 (7.4%). Changing the cutoff to 0.75 MoM resulted in 18 of 21 (85.7%) sensitivity and 74 of 2,515 (2.9%) false-positive rate. Using medians derived from whites to calculate MoM for the entire population resulted in higher false-positive rates. CONCLUSION: Nasal bone length expressed as MoM seems to be an useful ultrasound marker for Down syndrome in second-trimester fetuses with a high sensitivity and a low false-positive rate. LEVEL OF EVIDENCE: III.

OBJECTIVE: The purpose of this study was to determine the influence of race and ethnicity on the expected nasal bone length (NBL) based on biparietal diameter (BPD) measured in second-trimester fetuses. METHODS: We searched our ultrasound, obstetric, and cytogenetic databases for all second-trimester fetuses with measured NBLs. Fetuses with Down syndrome were identified and excluded from the analysis. Linear regression curves were generated for NBL by BPD according to race and ethnicity. Categories used were African American, Hispanic, Asian, and white. Analysis of variance was used to compare mean variation of observed from expected NBL by BPD according to race and ethnicity. RESULTS: There were 717 fetuses with NBL-by-BPD pairs who were available for analysis in our population, including 139 African American, 58 Hispanic, 22 Asian, and 498 white fetuses. Nasal bone length was highly correlated with BPD for each race (P < .001). Mean variances of observed from expected NBL by BPD were statistically different according to race or ethnicity (P = .0092). CONCLUSIONS: Race and ethnicity significantly affect the mean regression line of expected NBL by BPD among fetuses in the second trimester. Genetic sonographic norms, therefore, appear to require race- and ethnicity-specific formulas for NBL.

OBJECTIVE: To determine the frequency of echogenic intracardiac focus (EIF) by race/ethnicity. METHODS: We performed a retrospective analysis from January 1996 through June 2003. We reviewed all initial sonograms from 14 to 23 weeks gestation in singleton pregnancies. Mothers on admission for delivery provided race/ethnicity. RESULTS: There were 8207 ultrasounds and deliveries that met study criteria. There were 4636 (56.5%) Caucasian, 2087 (25.4%) African-American, 1261 (15.4%) Hispanic and 223 (2.7 %) Asian subjects. There were 347 (4.2%) EIF detected. The frequency by race/ethnicity varied significantly (p < 0.0001). CONCLUSIONS: This large, population-based study showed that fetuses born to Asian mothers were significantly more likely to have an EIF. This racial difference should be taken into account when counseling patients about the potential for Down syndrome.

OBJECTIVE: The purpose of this study was to compare the mitral valve-tricuspid valve distance in second-trimester fetuses with normal cardiac anatomy versus those fetuses with endocardial cushion defects. STUDY DESIGN: We identified fetuses between 16 and 24 weeks of gestation. The distance between the insertions of the medial leaflets of the mitral and tricuspid valves were obtained. Linear regression curves were generated. RESULTS: The mean mitral valve-tricuspid valve distance for 86 fetuses with normal cardiac anatomy was 2.02 mm, compared with 0.37 mm in 13 fetuses with endocardial cushion defects ( P = .0001). Linear regression curve correlating mitral valve-tricuspid valve distance with gestational age showed a gradual slope (R 2 = 0.28; P < .0001). With a mitral valve-tricuspid valve distance < 5th percentile as a marker for the diagnosis of endocardial cushion defect gave a sensitivity of 69.2%, a specificity of 100%, a positive predictive value of 100%, a negative predictive value of 95.6%, and a false-positive rate of 0% ( P = .0001). CONCLUSION: The mitral valve-tricuspid valve distance is useful clinically in the detection of endocardial cushion defects in second-trimester fetuses.

OBJECTIVE: We investigated the observed and expected Down syndrome livebirths in the US from 1989 to 2001. STUDY DESIGN: Using birth certificate data, we recorded maternal age-specific live births from 1989 to 2001, and stratified them by women 15 to 34 and 35 to 49 years old. We estimated Down syndrome live births from 1989 to 2001, assuming no terminations. We recorded Down syndrome live births by year from 1989 to 2001. RESULTS: Despite an expected 1.32-fold increase in Down syndrome live birth rates from 1989 to 2001, Down syndrome live births actually declined. In 1989, the rate of Down syndrome cases was 15% lower than expected, decreasing to 51% by 1998. Women 15 to 34 had 45% fewer affected pregnancies in 2001, while women 35 to 49 had 53% fewer in 2001. We estimated that Down syndrome live births decreased from 3962 in 1989 to 3654 in 2001. CONCLUSION: Down syndrome live births declined in the US despite an expected increase caused by delayed or extended childbearing.

OBJECTIVE: The fetal mechanical PR interval obtained via pulsed Doppler has previously been demonstrated to correlate with electrocardiographic PR interval measured in the neonate. We sought to further analyze the influence of fetal heart rate and gestational age upon the fetal mechanical PR interval. METHODS: We searched our database for mechanical PR intervals, which were obtained during fetal echocardiography performed in our antenatal diagnostic unit. We included fetuses with a normal cardiac structural survey. The mechanical PR interval is measured from the A wave of the mitral valve to the beginning of ventricular systole corresponding to the opening of the aortic valve. Linear regression curves were generated to examine the correlation of mechanical PR interval with gestational age and fetal heart rate. Analysis of variance was used to compare the mean variation across three gestational age groups: 17-21.9 weeks (n = 24), 22-25.9 weeks (n = 52) and 26-38 weeks (n = 20). RESULTS: Mechanical PR intervals were measured in 96 fetuses with normal fetal echocardiography. The mechanical PR interval was 123.9 +/- 10.3 ms (mean +/- SD), with a range of 90-150 ms. Linear regression curves correlating mechanical PR interval with fetal heart rate and gestational age demonstrated a flat slope with R2 = 0.016, p = 0.22 and R2 = 0.0004, p = 0.85, respectively. The mechanical PR interval measured over the three gestational ages was as follows (mean +/- SD): 122.3 +/- 10.5 ms for 17-21.9 weeks; 125.0 +/- 9.6 ms for 22-25.9 weeks; and 123.1 +/- 11.9 ms for 26-38 weeks. Analysis of variance revealed no difference among the mechanical PR interval means measured over the three gestational age groups (p = 0.53). CONCLUSIONS: Fetal mechanical PR interval ranges from 90 to 150 ms in fetuses with sonographically normal fetal cardiac structure and rate. The mechanical PR interval appears to be independent of gestational age and fetal heart rate.

OBJECTIVE: To compare maternal and fetal outcomes after elective repeat Cesarean section versus a trial of labor in women after one prior uterine scar. STUDY DESIGN: All women with a previous single low transverse Cesarean section delivered at term with no contraindications to vaginal delivery were retrospectively identified in our database from January 1995 to October 1998. Outcomes were first analyzed by comparing mother-neonate dyads delivered by elective repeat Cesarean section to those undergoing a trial of labor. Secondarily, outcomes of mother-neonatal dyads who achieved a vaginal delivery or failed a trial of labor were compared to those who had elective repeat Cesarean delivery. RESULTS: Of 1408 deliveries, 749/927 (81%) had a successful vaginal birth after a prior Cesarean delivery. There were no differences in the rates of transfusion, infection, uterine rupture and operative injury when comparing trial of labor versus elective repeat Cesarean delivery. Neonates delivered by elective repeat Cesarean delivery were of earlier gestation and had higher rates of respiratory complications (p < 0.05). Mother-neonatal dyads with a failed trial of labor sustained the greatest risk of complications. CONCLUSION: Overall, neonatal and maternal outcomes compared favorably among women undergoing a trial of labor versus elective repeat Cesarean delivery. The majority of morbidity was associated with a failed trial of labor. Better selection of women likely to have a successful vaginal birth after a prior Cesarean delivery would be expected to decrease the risks of trial of labor.