Prefrontal space ratio in second- and third-trimester screening for trisomy 21

Second trimester soft markers: still worth to be mentioned?

Despite the widespread use of cell-free DNA in screening for trisomy 21, soft markers continue to be assessed in the second trimester, leading to confusion about how they affect the risk of trisomy 21, especially after an earlier screening test such as cell-free DNA screening. In this review, we provide an overview of commonly used second trimester soft markers, explain how they can be used to calculate the risk for trisomy 21, and discuss what other chromosomal or structural abnormalities might be associated with these markers. We especially focus on pathogenic copy number variants as these, in aggregate, are common and are very difficult to detect using cfDNA or even standard karyotyping.

Fetal Profile Markers for the Detection of Robin Sequence in Fetuses with Retrognathia

OBJECTIVE

To determine whether the prefrontal space ratio (PSFR), inferior facial (IFA) and maxilla-nasion-mandible angle (MNM), and the fetal profile line (FPL) are helpful in identifying fetuses with Robin sequence (RS) in cases with isolated retrognathia, and thus better predict the likelihood of immediate need for postnatal respiratory support.

METHODS

This was a retrospective matched case-control study of fetuses/infants with isolated retrognathia with or without RS receiving pre- and postnatal treatment at the University Hospital of Tübingen, Germany between 2008 and 2020. The PFSR, IFA, MNM, and FPL were measured in affected and normal fetuses according to standardized protocols. Cases were stratified into isolated retrognathia and RS.

RESULTS

21 (n=7 isolated retrognathia, n=14 RS) affected fetuses and 252 normal fetuses were included. Their median gestational age at ultrasound examination was 23.6 and 24.1 weeks, respectively. In fetuses with isolated retrognathia and RS, the PSFR, IFA, and FPL were significantly different from the normal population. At a false-positive rate of 5%, the detection rate was 76.2% for the PFSR, 85.7% for the IFA, and 90.5% for both parameters combined. However, all parameters failed to distinguish between isolated retrognathia and RS.

CONCLUSION

PSFR and IFA are simple markers for identifying retrognathia prenatally. However, they are not helpful for the detection of RS in fetuses with isolated retrognathia. Therefore, delivery should take place in a center experienced with RS and potentially life-threatening airway obstruction immediately after birth.

Development and Validation of a Deep Learning Model to Screen for Trisomy 21 During the First Trimester From Nuchal Ultrasonographic Images

IMPORTANCE

Accurate screening of trisomy 21 in the first trimester can provide an early opportunity for decision-making regarding reproductive choices.

OBJECTIVE

To develop and validate a deep learning model for screening fetuses with trisomy 21 based on ultrasonographic images.

DESIGN, SETTING, AND PARTICIPANTS

This diagnostic study used data from all available cases and controls enrolled at 2 hospitals in China between January 2009 and September 2020. Two-dimensional images of the midsagittal plane of the fetal face in singleton pregnancies with gestational age more than 11 weeks and less than 14 weeks were examined. Observers were blinded to subjective fetus nuchal translucency (NT) marker measurements. A convolutional neural network was developed to construct a deep learning model. Data augmentation was applied to generate more data. Different groups were randomly selected as training and validation sets to assess the robustness of the deep learning model. The fetal NT was shown and measured. Each detection of trisomy 21 was confirmed by chorionic villus sampling or amniocentesis. Data were analyzed from March 1, 2021, to January 3, 2022.

MAIN OUTCOMES AND MEASURES

The primary outcome was detection of fetuses with trisomy 21. The receiver operating characteristic curve, metrics of accuracy, area under the curve (AUC), sensitivity, and specificity were used for model performance evaluation.

RESULTS

A total of 822 case and control participants (mean [SD] age, 31.9 [4.6] years) were enrolled in the study, including 550 participants (mean [SD] age, 31.7 [4.7] years) in the training set and 272 participants (mean [SD] age, 32.3 [4.7] years) in the validation set. The deep learning model showed good performance for trisomy 21 screening in the training (AUC, 0.98; 95% CI, 0.97-0.99) and validation (AUC, 0.95; 95% CI, 0.93-0.98) sets. The deep learning model had better detective performance for fetuses with trisomy 21 than the model with NT marker and maternal age (training: AUC, 0.82; 95% CI, 0.77-0.86; validation: AUC, 0.73; 95% CI, 0.66-0.80).

CONCLUSIONS AND RELEVANCE

These findings suggest that this deep learning model accurately screened fetuses with trisomy 21, which indicates that the model is a potential tool to facilitate universal primary screening for trisomy 21.

Reference standards for facial measurements in early third trimester South African fetuses, and the effect of maternal and fetal characteristics

Fetal alcohol spectrum disorder (FASD) is a major problem worldwide and dysmorphic facial features may be a prenatal biomarker for FASD. Deviations from normal facial development cannot be explored before establishing the normal variation in a specific population, since ethnic differences may exist.Objectives: Main objective: to establish reference standards for 23 facial measurements on 3D ultrasound volumes obtained between days 196 and 224 of gestation in healthy unexposed South African fetuses from an area with historically high alcohol consumption prevalence and a population group with no existing normative values. Secondary objective: to assess the confounding effect of maternal and fetal characteristics.Design: This study involves 97 women (including 43 smokers) who had been enrolled in the Safe Passage Study (SPS), a large prospective multinational cohort study assessing the effects of prenatal alcohol exposure. They had adequate 3 D ultrasound volumes of the fetal face acquired at 28⁺⁰-31⁺⁶weeks in singleton pregnancies without comorbidities, congenital abnormalities or exposure to alcohol, marijuana, or methamphetamines from 4 weeks before conception.Participants, materials, setting, methods: The participants were recruited from two residential areas of low socioeconomic status in Cape Town. Meticulous information was collected on maternal and pregnancy characteristics, including alcohol use at different time points. Gestational age (GA) was based on ultrasound biometry before 24 weeks, and 3D ultrasound volumes were acquired trans-abdominally from a sagittal and axial plane of the fetal face. Volumes were independently assessed offline by two observers and the image with the best landmark definition was used for 23 facial measurements, representing features previously described in children with FASD. The relation to the exact GA was assessed by regression analysis, the expected mean value and standard error of the estimate (SEE) was determined to transform all raw measurements into z-scores, and the effect of possible confounders on z-scores was assessed by ANOVA.Results: Ten variables changed significantly with advancing GA (extraocular diameter, anteroposterior, medio-lateral and supero-inferior ocular diameter, ocular volume, interlens distance, prenasal thickness, nasal bone length, nose length and nose protrusion) and thirteen did not (interocular distance; interocular: extraocular diameter ratio, prenasal thickness: nasal bone length ratio, pronasal-subnasal distance, subnasal-mouth distance, philtrum length, upper vermillion thickness, nose-philtrum angle, maxillary angle, facial height, facial protrusion, frontomaxillary facial angle and maxilla-nasion-mandible angle). Reference values (expected mean and SEE) for the 23 measurements were established for each day.The z-scores of all facial measurements were not independently affected by maternal age, parity, gravidity, smoking or body mass index, but infant sex and birthweight z-score significantly influenced several z-scores (infant sex for extraocular, medio-lateral, and supero-inferior ocular diameter, ocular volume, prenasal thickness and nose protrusion; birthweight z-score for extraocular diameter, interocular and interlens distance, nose protrusion and maxillary angle).Limitations: GA was not always confirmed by first trimester ultrasound and some measurements could not be obtained in all cases due to suboptimal image quality. The cohort included few heavy smokers so an effect of heavy or continued smoking cannot be ruled out, and the effect of ethnicity was not assessed.Conclusions: These are the first local reference standards for fetal facial measurements and, to our knowledge, the first reference standards for the supero-inferior ocular diameter, face protrusion, upper vermillion thickness, maxillary angle, and nose-philtrum angle. They were broadly in keeping with published references, with small discrepancies explained by minor differences in technique. Even in this narrow GA window, the distribution of many variables changed over time and normal variation was significantly influenced by fetal sex and birthweight z-score. The possible confounding effect of these factors needs to be considered when assessing the impact of harmful exposures like alcohol on facial development.

Ultrasonographic study of fetal facial profile markers during the first trimester

Background

To establish reference ranges of fetal facial profile markers and study their correlations with crown-rump length (CRL) during the first trimester (11 ~ 13+ 6 weeks’ gestation) in a Chinese population.

Methods

Ultrasonographic images of measuring fetal nuchal translucency (NT) were retrospectively selected randomly in normal fetuses whose parents were both Chinese. The facial markers included inferior facial angle (IFA), maxilla-nasion-mandible (MNM) angle, facial maxillary angle (FMA) and profile line (PL) distance. These markers were measured through ViewPoint 6 software by two experienced sonographers.

Results

Three hundred and eighty fetuses were selected. The ICCs (95 % CI) of intra-operator 1 reproducibility of IFA, MNM angle, FMA, PL distance were 0.944 (0.886 ~ 0.973), 0.804 (0.629 ~ 0.902), 0.834 (0.68 ~ 0.918) and 0.935 (0.868 ~ 0.969), respectively. The ICCs (95 % CI) of intra-operator 2 reproducibility of IFA, MNM angle, FMA, PL distance were 0.931 (0.857 ~ 0.967), 0.809 (0.637 ~ 0.904), 0.786 (0.600 ~ 0.892) and 0.906 (0.813 ~ 0.954), respectively. The ICCs (95 % CI) of inter-operator reproducibility of IFA, MNM angle, FMA, PL distance were 0.885 (0.663 ~ 0.953), 0.829 (0.672 ~ 0.915), 0.77 (0.511 ~ 0.891) and 0.844 (0.68 ~ 0.925), respectively. The average ± SD of IFA, MNM angle, FMA and PL distance were 80.2°±7.25°, 4.17°±1.19°, 75.36°±5.31°, 2.78 ± 0.54 mm, respectively. IFA and PL distance significantly decreased with CRL, while MNM angle and FMA significantly increased with CRL.

Conclusions

It was feasible to measure fetal facial markers during the first trimester. In Chinese population, the reference ranges of IFA, MNM angle, FMA and PL distance were 80.2°±7.25°, 4.17°±1.19°, 75.36°±5.31°, 2.78 ± 0.54 mm, respectively, and the measurements were found to correlate with CRL.

Fetal profile in fetuses with open spina bifida

OBJECTIVE

To determine whether the frontomaxillary facial (FMF) angle and the prefrontal space ratio (PFSR) are helpful in screening for open spinal defects by ultrasound in the second and third trimesters of pregnancy.

METHODS

The FMF angle and the PFSR were measured in fetuses with spina bifida according to standardized protocols. The normal range of the PFSR was previously published by our group. To determine the normal values for the FMF angle in the second and third trimesters of pregnancy, we used the same stored images from the above-mentioned study.

RESULTS

71 affected and 279 normal fetuses were included in this study. Median gestational ages in the two groups were 21.1 weeks and 21.6 weeks, respectively. In fetuses with spina bifida, the FMF angle was significantly smaller than in the normal population (72.9° versus 79.6°). However, the measurement was below the fifth centile in only 22.5% of the affected fetuses. The PFSR was similar in both groups.

CONCLUSIONS

The FMF angle is smaller in second and third trimester fetuses with open spina bifida. However, the difference is not large enough to implement this marker in current screening programs.

Measurement of inferior facial angle and prefrontal space ratio in first trimester fetuses with aneuploidies: a retrospective study

Objective To determine whether the measurement of inferior facial angle (IFA) and prefrontal space ratio (PFSR) in two-dimensional (2D) ultrasound images in the first trimester of pregnancy is reliable and to describe these markers in normal and aneuploid fetuses. Methods IFA and PFSR were measured in stored 2D midsagittal images of 200 normal and 140 aneuploid fetal profiles between 11 + 0 and 13 + 6 weeks of gestation. Limits of agreement (LOAs) and intraclass correlation coefficients (ICCs) for inter- and intraobserver differences were calculated. Results The mean IFA in normal fetuses was 76.5° ± 6.3. Between the two measurement rounds of the same observer, the LOAs were -5.4 to 7.1 (obs. 1) and 7.4 to 8.4 (obs. 2). For IFA measurements by the same observer the ICC was 0.88 (obs. 1) and for measurements by two different observers the ICC was 0.74. The mean PFSR was 0.76 ± 0.40 and the intraobserver LOAs were -0.372 to 0.395 (obs. 1) and -0.555 to 0.667 (obs. 2). For PFSR measurements by the same observer the ICC was 0.89 (obs. 1) and for measurements by two different observers the ICC was 0.65. Among aneuploid fetuses, IFA was below the normal range in one third of the cases with trisomy 18. PFSR was below the 95% prediction limit in 16.2% of fetuses with trisomy 21% and 17.9% of fetuses with trisomy 18. Conclusion IFA can be reliably measured in 2D ultrasound images in the first trimester of pregnancy with a high interobserver agreement and may provide information about retrognathia associated with various syndromes and aneuploidies at early stages of pregnancy.

Sphenofrontal distance in euploid and aneuploid fetuses

OBJECTIVE

To examine the sphenofrontal distance (SFD) in a large series of aneuploid fetuses in the second and third trimesters and compare findings with those of a euploid population.

METHODS

The database at our unit was searched to identify pregnancies with a diagnosis of trisomy 21, 18 or 13, triploidy or Turner syndrome after 15 weeks' gestation. Stored ultrasound images obtained between 19 and 22 weeks were reviewed. For the normal population, two euploid fetuses matched for gestational age were selected randomly for each aneuploid case. The SFD was measured from the anterior edge of the sphenoid bone to the lowest posterior edge of the frontal bone using on-screen calipers. The SFD measurement was parallel to the long axis of the maxilla. If the sphenoid bone did not extend superiorly enough for direct measurement of the SFD, a tangential line was drawn at the anterior wall of the sphenoid bone and extended cranially. In these cases, the distance between the extended line and the frontal bone was measured. One operator measured the SFD twice and was blinded to the results and karyotype.

RESULTS

The study population consisted of 591 pregnancies: 394 euploid fetuses, 122 fetuses with trisomy 21, 45 with trisomy 18, 16 with trisomy 13, eight with Turner syndrome and six with triploidy. For both euploid and aneuploid groups, mean gestational age at examination was 22.8 (range: euploid, 15.0-40.7; aneuploid, 15.0-40.3) weeks. For euploid fetuses, mean SFD was 1.27 cm and measurements ranged from 0.53 cm to 2.56 cm. SFD was significantly dependent on gestational age (SFD = 0.138 + 0.005 × gestational age, P < 0.001, r = 0.802). Mean SFD was significantly smaller in each aneuploid group compared with the euploid population (trisomies 21, 18 and 13: all P < 0.001; triploidy: P = 0.026; Turner syndrome: P = 0.047). For 32 (26.2%), nine (20.0%) and six (37.5%) fetuses with trisomy 21, 18 and 13, respectively, SFD was < 5^th percentile. Only one (12.5%) fetus with Turner syndrome and none with triploidy had SFD < 5^th percentile.

CONCLUSION

In aneuploid fetuses, the SFD is smaller than in their euploid counterparts. However, for a false-positive rate of 5%, the detection rate of trisomy 21 is only 26%. Therefore, using the method we have proposed, it is unlikely that this marker will play a major role in second- and third-trimester screening for aneuploidy. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Prefrontal Space Ratio—A Novel Ultrasound Marker in the Second Trimester Screening for Trisomy 21: Systematic Review and Meta-Analysis

To determine the value of prefrontal space ratio (PFSR) as a novel soft marker in the second-trimester screening for trisomy 21, PubMed and two other databases were searched electronically for the relevant materials published between January 2000 and December 2015. Four studies were included in the mini meta-analysis. All of the studies were retrospective and of high quality. Overall sample size was 293 trisomy 21 and 609 euploid fetuses. The pooled mean PFSR was 0.322 (95% confidence interval [CI], 0.256-0.388) and 1.205 (95% CI, 0.997-1.413) in trisomy 21 and euploid fetuses, respectively. This ratio was found to be significantly lower in trisomy 21 fetuses compared to euploid ones ( P < .0001). The pooled detection rate was 87.2% at a false-positive rate of 5%. Pooled positive and negative likelihood ratios measured 17.2 and 0.146, respectively. In conclusion, PFSR is an efficient marker that may be investigated in the second-trimester ultrasound screening for trisomy 21.

Assessment of Midfacial Hypoplasia in Down Syndrome Fetuses - Validity of a Two-Line Approach and Introduction of a Novel Angle (Maxilla-Mandible-Nasion Angle)

PURPOSE

To scrutinize the validity of a novel angle (maxilla-mandible-nasion angle, MMN) as objective proof of midfacial hypoplasia in trisomy 21 fetuses.

MATERIALS AND METHODS

Volume data sets of 2(nd) trimester fetuses were reviewed in this retrospective study. After achievement of the correct midsagittal position, the fetal profile line (FP line) and the mandibulo-maxillary line (MML) were applied and the resulting angle was calculated. Additionally, the prefrontal space ratio (PFSR) was assessed. Both measurements were obtained from 401 euploid fetuses and 42 fetuses with trisomy 21. Values for MMN and PFSR<5(th) percentile were considered abnormal.

RESULTS

The study included 443 fetuses with a mean gestational age of 21.3 weeks (range: 14.0-26.3). The MMN angle sufficiently identified hypoplasia of the midface in trisomy 21 fetuses (mean: 14.6°; range: 10.1°- 22.0°) compared to controls (mean: 20.5°; range: 17.3°-23.7°; p<0.0001). Concomitantly, the PFSR of Down syndrome fetuses was significantly lower (mean: 0.53; range: 0.21-1.22) than in euploid individuals (1.38; range: 0.54-2.23; p<0.0001).

CONCLUSION

Calculation of the novel MMN angle in 2(nd) trimester fetuses reliably allows rapid assessment of craniofacial anatomy in order to rule out the midfacial hypoplasia frequently found in trisomy 21.

Fetal facial profile markers of Down syndrome in the second and third trimesters of pregnancy

OBJECTIVES

To investigate the use of the maxilla-nasion-mandible (MNM) angle and fetal profile (FP) line to assess the degree of midfacial hypoplasia in Down-syndrome fetuses in the second and third trimesters of pregnancy.

METHODS

The MNM angle and FP line were measured retrospectively in stored two-dimensional images or three-dimensional volumes of fetuses with Down syndrome. Data collected from January 2006 to July 2013 were retrieved from the digital databases of participating units. The MNM angle was expressed as a continuous variable (degrees) and the FP line as positive, negative or zero. Measurements were obtained from stored images in the midsagittal plane by two experienced examiners and compared with our previously reported normal ranges for euploid fetuses. A MNM angle below the 5(th) centile of the reference range and a positive or negative FP line were considered as abnormal.

RESULTS

A total of 133 fetuses with Down syndrome were available for analysis, eight of which were subsequently excluded because of inadequate images. The MNM angle was not influenced by gestational age (P = 0.48) and was significantly smaller in Down-syndrome fetuses than in euploid fetuses (mean, 12.90° vs 13.53°, respectively; P = 0.015). The MNM angle was below the 5th centile for euploid fetuses in 16.8% of fetuses with Down syndrome (P < 0.01). In the cohort of Down-syndrome fetuses, a positive FP line was present in 41.6% of cases (with a false-positive rate (FPR) of 6.3%) and was positively correlated with Down syndrome and gestational age (P < 0.01). There was no case with a negative FP line. In cases of Down syndrome, a positive FP line was correlated with a small MNM angle (P < 0.01).

CONCLUSIONS

A small MNM angle and a positive FP line can be regarded as novel markers for Down syndrome. The FP line is an easy marker to measure, has a low FPR, does not require knowledge of normal reference values and has the potential to differentiate between Down syndrome and trisomy 18, as, in the latter, the FP line is often negative.

Facial profile markers in second- and third-trimester fetuses with trisomy 18

OBJECTIVES

To evaluate nasal bone length (NBL), maxilla-nasion-mandible (MNM) angle, fetal profile (FP) line, prenasal thickness (PT), prenasal thickness to nasal bone length (PT:NBL) ratio and prefrontal space ratio (PFSR) as markers of trisomy 18 in the second and third trimesters of pregnancy.

METHODS

The NBL, MNM angle, FP line, PT, PT:NBL ratio and PFSR were measured retrospectively from stored two-dimensional images or three-dimensional volumes of trisomy-18 fetuses, and were compared with our previously reported normal ranges for euploid fetuses. Additional ultrasound findings were noted at initial routine second-trimester scan and at subsequent advanced ultrasound examination performed after referral for karyotyping.

RESULTS

A total of 43 trisomy-18 fetuses were included in the analysis. At initial examination, median gestational age was 21 + 2 weeks. NBL and PT were correlated with gestational age (P < 0.001), but the other markers were not. Mean NBL, MNM angle, PT, PT:NBL ratio and PFSR were 3.76 mm, 16.67°, 4.25 mm, 1.39 and 0.87, respectively. The FP line was zero (normal) in 53.7% of cases and negative (abnormal) in 46.3%. All markers were significantly associated with trisomy 18, with the PT:NBL ratio yielding the highest detection rate (88.4%) followed by NBL (83.7%), MNM angle (56.4%), FP line (46.3%), PT (27.9%) and the PFSR (20.5%) (for a 5% false-positive rate for the continuous variables). Various combinations of the four best markers (NBL, FP line, MNM angle and PT:NBL ratio) yielded detection rates of between 72% and 95%. Structural anomalies were not detected in 22% of fetuses at the initial scan and in 2% at the advanced scan.

CONCLUSIONS

The PT:NBL ratio and NBL are robust second- and third-trimester markers for trisomy 18. A negative FP line has a 0% false-positive rate and the potential to differentiate between trisomy 18 and Down syndrome, as in the latter the FP line is often positive. No major anomaly was observed at the initial scan in about a quarter of trisomy-18 fetuses, underlining the role of second-trimester facial marker evaluation.

Facial markers in second- and third-trimester fetuses with trisomy 18 or 13, triploidy or Turner syndrome

OBJECTIVE

To examine the effectiveness of nasal bone (NB) evaluation (including NB length (NBL)), prenasal thickness (PT) measurement, the PT:NBL ratio and the prefrontal space ratio (PFSR) in the identification of fetuses with trisomy 18 or 13, triploidy or Turner syndrome.

METHODS

This was a retrospective study using stored midsagittal two-dimensional images of the facial profile of fetuses with trisomy 18 or 13, triploidy or Turner syndrome in the second and third trimesters. For images of acceptable quality, measurements were obtained of NBL (where NB was present), PT, the PT:NBL ratio and PFSR, and these measurements were compared with previously published normal ranges.

RESULTS

The search of databases identified 189 fetuses that met the study criteria: 132 (69.8%) with trisomy 18, 40 (21.2%) with trisomy 13, 10 (5.3%) with triploidy and seven (3.7%) with Turner syndrome. The NB was either absent or its measurement was below the 5(th) centile in 67 (50.8%), 20 (50.0%), five (50.0%) and two (28.6%) of the fetuses with trisomy 18, trisomy 13, triploidy and Turner syndrome, respectively. The PT measurement was above the 95(th) centile in 24 (18.2%), six (15.0%), one (10.0%) and one (14.3%) of the affected fetuses, respectively. The PFSR was abnormal in 72 (54.5%), 29 (72.5%), seven (70%) and four (57.1%) of the cases and the PT:NBL ratio was above the 95(th) centile or the nasal bone was absent in 72 (54.5%), 20 (50.0%), six (60.0%) and four (57.1%) cases, respectively.

CONCLUSION

Although each of the facial markers considered provides some useful information in screening for trisomy 18, trisomy 13, triploidy and Turner syndrome, the performance of none of the markers appears to be as good as that in screening for trisomy 21.

Nasal bone length, prenasal thickness, prenasal thickness-to-nasal bone length ratio and prefrontal space ratio in second- and third-trimester fetuses with Down syndrome

OBJECTIVES

To evaluate nasal bone length (NBL), prenasal thickness (PT), prenasal thickness-to-nasal bone length (PT-NBL) ratio and prefrontal space ratio (PFSR) as markers for Down syndrome in the second and third trimesters.

METHODS

NBL, PT, PT-NBL ratio and PFSR were measured retrospectively in stored two-dimensional images or three-dimensional volumes (corrected to the mid-sagittal plane) of fetuses with Down syndrome, which were retrieved from the digital databases of participating units. Measurements were performed on the stored images and volumes by two experienced operators, and the values obtained were compared to our previously reported normal ranges for euploid fetuses in order to assess the detection rates for Down syndrome.

RESULTS

A total of 159 fetuses with Down syndrome were included in the analysis, six of which were excluded because of inadequate available images. Median maternal age was 36.0 years and median gestational age was 23 + 1 weeks. NBL and PT were correlated with gestational age (P < 0.001), but the PT-NBL ratio and PFSR were not. Mean NBL, PT, PT-NBL ratio and PFSR were 4.42 mm, 5.56 mm, 1.26 and 0.34, respectively. The nasal bone was absent in 23 (15.4%) cases. As a marker for Down syndrome, the PT-NBL ratio yielded the highest detection rate (86.2%), followed by PFSR (79.7%), PT (63.4%) and NBL (61.9%). All markers were abnormal in 33.6% of cases, whilst all were normal in 4.7%. At least one of the four markers was abnormal in 95.3%, and either the PT-NBL ratio or PFSR was abnormal in 93.8%. Detection rates were not related to gestational age.

CONCLUSIONS

The PT-NBL ratio and PFSR are robust second- and third-trimester markers for Down syndrome. Both provide high detection rates and are easy to use, as the cut-off for normality is constant throughout gestation. Ltd.

Trends in Serial Measurements of Ultrasound Markers in Second and Third Trimester Down Syndrome Fetuses

OBJECTIVES

To evaluate trends of nasal bone length (NBL), prenasal thickness (PT), nuchal fold (NF), prenasal thickness to nasal bone length (PT-NBL) ratio, and prefrontal space ratio (PFSR), measured serially in second- and third-trimester Down syndrome (DS) fetuses.

METHODS

Prenatal databases were searched for cases of continuing DS pregnancies with serial measurements, taken at least two weeks apart. Trends were plotted on previously reported normal ranges.

RESULTS

Serial measurements were available in 25 Down syndrome fetuses. Median gestational age (GA) was 25 weeks; average number of visits per case was 2.44, with a median interval of 39 days between investigations. In DS fetuses, NBL and PT showed fairly stable trends with gestation. PFSR, but especially NF, had a more unpredictable trend. The PT-NBL ratio was the most stable marker, remaining unchanged in 95% of cases. NBL, PT, and NF showed more deviance from the normal range with advancing gestation, but MoM values remained stable. All but two fetuses had ultrasound markers or structural anomalies, especially heart defects.

CONCLUSIONS

The PT-NBL ratio is the most constant DS marker throughout gestation, following a predictable trend.

The cavum septi pellucidi in euploid and aneuploid fetuses

OBJECTIVE

To examine whether the cavum septi pellucidi (CSP) is larger in second- and third-trimester fetuses with chromosomal abnormalities than in euploid fetuses.

METHODS

This was a retrospective study utilizing stored two-dimensional images of second- and third-trimester fetuses between 18 and 40 weeks' gestation from three centers in Germany. The width of the CSP was measured by placing the calipers on the inner portion of its lateral borders. Two operators, both of whom were blinded to the fetal karyotype and to the measurements obtained by the other, measured the CSP width. The normal range in euploid fetuses was computed based on the biparietal diameter (BPD) by applying univariate regression analysis. The CSP width in euploid and aneuploid fetuses was transformed into Z-scores and compared using Student's t-test. Univariate regression analysis was used to determine the dependency of Z-score on head biometry.

RESULTS

The study population consisted of 406 singleton pregnancies, 267 with euploid fetuses, 81 with trisomy 21, 50 with trisomy 18 and eight with trisomy 13. In the euploid group, the mean CSP width was 4.5 (range, 1.8-7.4) mm. Regression analysis showed a significant dependency of CSP width on BPD (CSP width = 0.658 + (0.064 × BPD), r = 0.781, P < 0.0001; both parameters in mm). The mean CSP width increased from 3.2 to 7.1 mm for BPD values of 40 to 100 mm, respectively. In the groups of fetuses with trisomy 21, 18 and 13, mean CSP width was 5.7 (range, 2.8-10.5), 7.9 (range, 3.5-12.8) and 5.8 (range, 4.0-9.0) mm, respectively. In 42.0% of the fetuses with trisomy 21, CSP width was above the 95(th) centile. In trisomy 18 and 13, CSP width was above the 95(th) centile in 92.0% and 37.5% of cases, respectively.

CONCLUSION

A large CSP width should prompt a detailed ultrasound examination to further assess the risk for chromosomal abnormalities.