Disappearance of enlarged nuchal translucency before 14 weeks gestation: relationship with chromosomal abnormalities and pregnancy outcome

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1 Ultrasound Obstet Gynecol 2004; 24: Published online in Wiley InterScience ( DOI: /uog.1103 Disappearance of enlarged nuchal translucency before 14 weeks gestation: relationship with chromosomal abnormalities and pregnancy outcome M. A. MÜLLER*, E. PAJKRT, O. P. BLEKER*, G. J. BONSEL and C. M. BILARDO* Departments of *Obstetrics and Gynaecology and Social Medicine, Academic Medical Centre, Amsterdam, The Netherlands and Department of Obstetrics and Gynaecology, University College Hospital, London, UK KEYWORDS: Down syndrome; first trimester; NT; nuchal translucency measurement; prenatal; serial; transient; ultrasound ABSTRACT Objective The aim of this study was to investigate the natural course of enlarged nuchal translucency (NT) and to determine if its disappearance before 14 weeks gestation is a favorable prognostic sign in relation to fetal karyotype and pregnancy outcome. Methods A total of 147 women with increased NT (> 95th centile) at first measurement were included in this study. A second measurement was performed in all cases, at an interval of at least 2 days. Both measurements were taken between and weeks. All women underwent chorionic villus sampling or amniocentesis for subsequent karyotyping. In those women with a normal karyotype, a fetal anomaly scan was performed at 20 weeks gestation. Pregnancy outcome was recorded in all cases. The finding of persistent or disappearing NT enlargement was analyzed in relation to fetal karyotype and pregnancy outcome. Results Of the 147 paired measurements, NT remained enlarged at the second measurement in 121 (82%) cases. An abnormal karyotype was found in 35% of these cases. In 26 (18%) fetuses the NT measurement was found to be below the 95th percentile at the second measurement and in only two of them an abnormal karyotype was found (8%). In the 103 chromosomally normal fetuses an adverse outcome (i.e. fetal loss or structural defects) was recorded in 22 fetuses with persistent enlargement (28%) and in four fetuses with disappearing enlargement (17%). Conclusions Disappearance of an enlarged NT before 14 weeks gestation is not a rare phenomenon and seems to be a favorable prognostic sign with respect to fetal karyotype. Overall, no significant difference in pregnancy outcome was found between chromosomally normal fetuses with persisting or disappearing NT enlargement. Copyright 2004 ISUOG. Published by John Wiley & Sons, Ltd. INTRODUCTION Since the introduction of nuchal translucency (NT) measurement in , screening using this sonographic marker has proven to be effective in the detection of Down syndrome and other chromosomal abnormalities 2. Adequate training of sonographers and the development of technical guidelines have led to improvement and uniformity of results in centers performing NT screening. Studies have shown that in normal fetuses the fluid collection known as NT increases with gestational age until about 13 weeks gestation 3 and usually disappears after 14 weeks 3,4. In the case of an enlarged NT the fluid collection also tends to disappear after this period 5, although sometimes it persists or even progresses into generalized hydrops or enlarged nuchal fold 6 8. Because of its transient nature NT measurement must be performed between 11 and 14 weeks gestation. Since the widespread introduction of NT screening an increasing number of pregnancies with enlarged NT are referred to specialized centers for fetal karyotyping. In our center we witnessed several cases of enlarged NT normalizing at subsequent scanning, within the period of weeks gestation. This may lead to conflicting risk assessments and complicate parental counseling, especially in young women in whom the initial NT enlargement was the only risk factor. The phenomenon of disappearing enlargement before 14 weeks has been reported by Maymon et al. 9 and more Correspondence to: Dr M. A. Müller, Department of Obstetrics and Gynaecology, Academic Medical Centre, PO Box 22660, 1100 DD, Amsterdam, The Netherlands ( m.a.muller@amc.uva.nl) Accepted: 3 May 2004 Copyright 2004 ISUOG. Published by John Wiley & Sons, Ltd. ORIGINAL PAPER

2 170 Müller et al. recently by Celentano et al. 10, but to our knowledge no prospective studies on the natural course of an enlarged NT within the week period have been published. The aim of this study was to investigate the natural course of enlarged NT at weeks of gestation and to determine if disappearance of an enlarged NT before 14 weeks is a favorable prognostic sign with respect to fetal karyotype and pregnancy outcome. METHODS The study population comprised pregnant women presenting with a viable singleton pregnancy and increased NT. Women attended our department for counseling because of advanced maternal age, for routine antenatal care or they were referred because of an increased NT found at another hospital. Experienced ultrasonographers, all trained and acknowledged by The Fetal Medicine Foundation, performed the scans. A transabdominal approach was used. Only if the NT could not be visualized or if fetal anatomy could not be adequately assessed was the examination carried out transvaginally. Women with confirmed enlarged NT at the first scan (NT1) and a gestational age of to14+ 0 weeks (crown rump length (CRL) between 38 and 84 mm) were included. The NT was considered enlarged if the measurement was above the 95th percentile for the given gestational age 12. Because in current clinical practice in NT screening the 95th percentile has been replaced by a risk assessment taking into account maternal age, this assessment was made for all measurements using the software developed by The Fetal Medicine Foundation. All women had a risk of more than 1 : 200 after the first scan, which is the risk cut-off for karyotyping used in our center. All women were counseled based on the results of the initial scan and were offered karyotyping by chorionic villus sampling (CVS) or amniocentesis. Women were asked to consent to a subsequent scan to monitor the course of the enlarged NT. A second NT measurement and risk assessment were performed in all cases (NT2), with an interval of at least 2 days from the first measurement. Both measurements were performed within the period of and weeks gestation. If the second measurement was above the 95th percentile it was classified as persistent NT enlargement, whereas if it was below the 95th percentile it was classified as disappearing NT enlargement. All fetuses were karyotyped. The majority of second scans were performed before karyotyping, but if karyotyping had already been performed the results were not available by the time of the second scan. In all chromosomally normal fetuses a fetal anomaly scan was performed at 20 weeks gestation. Pregnancy outcomes were obtained from our maternity unit and from outcome forms returned by participating women. Pregnancy outcome was defined as adverse (miscarriage, intrauterine death, termination of pregnancy) or live birth with no defects. RESULTS A total of 147 fetuses with a NT measurement above the 95th percentile had a repeat NT measurement. Mean maternal age at the time of the first scan was 34 (range, 19 42) years. Median gestational age at the time of the first scan was (range, to13+ 4) weeks, and median CRL was 52 (range, 38 77) mm. The NT measurement was repeated at a median interval of 6 (range, 2 24) days. The median gestational age at second measurement was (range, 11 14) weeks and the median CRL was 65 (range, 43 84) mm. Table 1 shows the data on the second NT measurement (NT2). Twentysix (18%) cases had disappearing NT while in 82% of cases the enlargement persisted. The tendency to disappear was more pronounced in those women in whom the second measurement was taken at an interval of more than 7 days (32% and 11%, respectively). The shift in risk assessment showed the same trend: in 33 (22%) women the calculated risk after the second measurement fell to less than 1 : 200. Chromosomal abnormalities In 44 (30%) fetuses an abnormal karyotype was diagnosed (Table 2). Data on the second NT measurement in relation to karyotype are shown in Table 3. In the group with persisting enlargement 42 cases had an abnormal karyotype (35%). In the group with disappearing enlargement two chromosomal abnormalities were found (8%). The calculated odds ratio (OR) for a persisting enlargement was 6.38 (95% CI, ). The same distribution of normal vs. abnormal karyotype was found when the risk assessment at the second measurement fell below 1 : 200. Pregnancy outcome in chromosomally normal fetuses In the 103 chromosomally normal pregnancies an adverse outcome was recorded in 25% of cases. Data on the second NT measurement in relation to pregnancy outcome are shown in Table 4. Table 1 Relationship between the second nuchal translucency (NT) measurement and the 95th percentile and the time interval between the two NT measurements Interval NT1 NT2 NT2 > P95 ( persisting NT ) (n, %) Relation to P95 NT2 P95 ( disappearing NT ) (n, %) Total (n) 7 days 89 (89) 11 (11) 100 > 7 days 32 (68) 15 (32) 47 Total 121 (82) 26 (18) 147 NT, nuchal translucency; NT1, first NT measurement; NT2, second NT measurement; P95, 95th percentile.

3 Enlarged NT disappearance and karyotype 171 Table 2 Fetal karyotype in 147 cases of enlarged nuchal translucency Karyotype n (%) Pregnancy outcome Normal 103 (70) Abnormal 44 (30) Trisomy TOP Trisomy TOP, 1 IUD Trisomy 13 5 TOP Trisomy 9 1 Miscarriage 45XO 6 TOP 47XXY 2 1 TOP, 1 alive and well 45XO, 46XX, 47XXX 1 Alive and well mosaicism Trisomy 20 mosaicism 1 TOP Unbalanced translocation 1 TOP Marker chromosome 1 TOP Total 147 IUD, intrauterine death; TOP, termination of pregnancy. Table 3 Relation between persisting or disappearing nuchal enlargement at second measurement and fetal karyotype Karyotype (n, %) Parameter Total Normal Abnormal Trisomy 21 Other NT2-P95 NT2 > P (65) 42 (35) 17 (14) 25 (21) NT2 P (92) 2 (8) 1 (4) 1* (4) Risk after NT2 > 1 : (63) 42 (37) 17 (15) 25 (22) 1 : (94) 2 (6) 1 (3) 1* (3) Total (70) 44 (30) 18 (12) 26 (18) *Trisomy 13: NT2 was 1.9 mm and the calculated risk 1 : 284. Additional anomalies at the second scan were facial cleft and abnormal extremities. NT2, second nuchal translucency measurement; P95, 95th percentile. In the group with disappearing enlargement at the second scan (n = 24) an adverse pregnancy outcome occurred in four (17%) cases. In 79 cases the NT remained above the 95th percentile at the second measurement (77%). In this group with persistent enlargement there were nine cases of spontaneous fetal loss (11%), six terminations of pregnancy (8%) because of severe hydrops or structural defects and seven live births with structural or genetic defects (9%). The overall incidence of adverse Adverse outcome (%) > 5.5 NT1 (mm) Figure 1 Incidence of adverse pregnancy outcome in fetuses with increased nuchal translucency (NT). NT1, first NT measurement. pregnancy outcome was thus 28% (OR 1.93; 95% CI, ). Table 5 shows details of the 26 cases with an adverse pregnancy outcome. Data on the first and second NT measurement are presented for each case. The incidence of adverse pregnancy outcome increased proportionally to the degree of initial enlargement, with incidences ranging from 16% in case of NT1 3.5 mm to 60% for NT1 > 5.5 mm(figure1). Subgroup analysis The difference in means of the NT measurement in the groups with persisting or disappearing enlargement was 0.9 mm (Mann Whitney U-test, P = 0.009) and therefore subgroup analysis was performed on fetuses showing an initial enlargement of 3.5 mm (99th centile) or > 3.5 mm. The results are presented in Table 6. The effect of nuchal fluid persistence at second measurement in relation to fetal outcome (adverse outcome including abnormal karyotype) was similar in both groups, irrespective of the degree of initial enlargement (OR 3.81 and 3.18, respectively). DISCUSSION The transient nature of nuchal fluid accumulation and its pathological enlargement have been described Table 4 Outcome of 103 chromosomally normal pregnancies in relation to persistence or disappearance of increased nuchal translucency before 14 weeks gestation NT2-P95 Miscarriage /IUD (%) TOP (%) Live birth with defects (%) Adverse pregnancy outcome (%) Live birth no defects (%) NT2 > P95 9 (11) 6 (8) 7 (9) 22 (28) 57 (72) NT2 P95 1 (4) 0 (0) 3 (13) 4 (17) 20 (83) Total 10 (10) 6 (6) 10 (10) 26 (25) 77 (75) IUD, intrauterine death; NT2, second nuchal translucency measurement; P95, 95th percentile; TOP, termination of pregnancy because of fetal defects or severe hydrops.

4 172 Müller et al. Table 5 Anomalies and adverse pregnancy outcome in 26 fetuses with enlarged nuchal translucency and normal karyotype Anomalies Total NT1 (mm) NT2 (mm) Time of diagnosis Pregnancy outcome NT2 P95 Noonan s syndrome Postnatal Alive Unspecified genetic syndrome* Postnatal Alive Esophageal atresia with fistula Postnatal Surgery after birth IUD 1 NT2 > P95 Transposition of great arteries and DORV Prenatal Surgery after birth DORV, pulmonary stenosis, VSD Postnatal Surgery after birth Ureter stenosis with hydronephrosis Prenatal Surgery after birth Unspecified genetic syndrome Postnatal Alive 22q11 deletion Prenatal Alive Cleft palate Postnatal Surgery after birth Diaphragmatic hernia Prenatal NND Adult polycystic kidney disease Prenatal TOP Achondrogenesis type Prenatal TOP Skeletal dysplasia Prenatal TOP Hydrothorax, hydrops Prenatal IUD at 20 weeks Fetal akinesia deformation sequence Prenatal TOP Severe hydrops, hygroma 5 Prenatal 2 TOP, 3 IUD Miscarriages/IUD 5 The symbols refer to the specification of abnormalities: *facial dysmorphism, developmental delay, transient hypertrophic cardiomyopathy, epileptic activity; 22q11 deletion diagnosed after birth; facial dysmorphism, small VSD and minimal pulmonary valve stenosis, macrocephaly, developmental delay, retinal coloboma. DORV, double outlet right ventricle; IUD, intrauterine death; NND, neonatal death; NT, nuchal translucency; NT1, first NT measurement; NT2, second NT measurement; P95, 95th percentile; TOP, termination of pregnancy; VSD, ventricular septal defect. Table 6 Subgroup analysis of NT1 3.5 and > 3.5 mm. Relation between persisting or disappearing nuchal enlargement at second measurement and pregnancy outcome* Parameter Abnormal outcome (%) Normal outcome (%) Total (n) OR (95% CI) NT1 3.5 mm NT2 > P95 16 (41) 23 (59) ( ) NT2 P95 2 (15) 11 (85) 13 NT1 > 3.5 mm NT2 > P95 48 (59) 34 (41) ( ) NT2 P95 4 (31) 9 (69) 13 Total *Abnormal outcome = abnormal karyotype or overall adverse pregnancy outcome. Normal outcome = normal karyotype and successful pregnancy outcome. OR, odds ratio; P95, 95th percentile. previously 9,12. The present study demonstrated that disappearance of an enlarged NT before 14 weeks gestation is not a rare phenomenon, occurring in about 1 : 5 (18%) fetuses. Normalization of NT after initial enlargement may lead to different risk assessments making genetic counseling of patients difficult, especially in younger women in whom excessive nuchal fluid accumulation is the only risk factor. Disappearing enlargement and chromosomal abnormalities Persistence of nuchal enlargement appears to be associated with a higher incidence of an abnormal karyotype as compared to when the enlargement disappears (35% vs. 8%; OR 6.38). In the case of nuchal enlargement it may be possible to identify more accurately those fetuses that are indeed at risk for chromosomal abnormalities by repeating the measurement. Repeat screening may lower the number of false-positives possibly at the cost of a slight decrease in sensitivity. In the present study one of the two chromosomal abnormalities in the group with disappearing NT that would have been missed was a trisomy 13. This pregnancy presented with a NT of 1.9 mm at the second scan ( weeks) and a calculated risk of 1 : 284. Additional abnormalities (facial cleft and deformities of the hands and feet) were observed at the second scan. These findings would have warranted karyotyping even in the presence of a reassuring second NT measurement. Obviously larger series are needed to confirm the observed trends in enlarged NT. This may enable the construction of an algorithm that combines the two risk assessments and may thereby improve selection of fetuses at increased risk and reduce the false-positive rate. Pregnancy outcome in chromosomally normal fetuses An enlarged NT is found in about 5% of chromosomally normal fetuses 2. These fetuses are known to have an increased risk of structural anomalies, intrauterine death and genetic syndromes In the group of karyotypically normal fetuses with enlarged NT, an adverse pregnancy outcome occurred in 25% of the cases. The chance of a live birth is known to decrease as NT thickness increases 15. In the present study the incidence of

5 Enlarged NT disappearance and karyotype 173 an adverse pregnancy outcome shows a similar trend, increasing proportionally to the degree of initial NT enlargement (Figure 1). Moreover, the present study indicates that fetuses with persisting excessive nuchal fluid collection may be twice as likely to have an adverse pregnancy outcome than those with NT normalization before 14 weeks gestation. However, this trend was not statistically significant, most likely because of the limited number of observations. These results suggest that when NT normalizes the frequency of adverse outcome still remains relatively high (17%). Interpretation of these data suggest that even in the presence of an underlying structural defect, excessive fluid collection is a temporary event that may resolve even before 14 weeks gestation. Subgroup analysis In the critical evaluation of our data we considered the possibility that the difference in prognosis between the groups with persistent or disappearing enlargement may be a consequence of difference in degree of enlargement at first measurement. A modest degree of enlargement is known to have a better prognosis 14 and is probably more likely to fall below the 95th percentile at second measurement. We therefore divided the study population into two subgroups with modest and more severe NT enlargement (Table 6). Although reduction of the sample size affected statistical significance, the trend towards a positive prognostic effect on fetal karyotype or pregnancy outcome of a vanishing enlargement was demonstrated in both groups. Pathophysiological considerations Due to the still unclear pathophysiology of an increased NT measurement interpretation of these data is difficult. For some chromosomal anomalies the pathophysiological background of excessive nuchal edema has been partly clarified: for instance, in trisomy 21 fetuses, both hyaluronic acid and collagen type IV are increased 16. The genes encoding the majority of these polypeptide chains are located on chromosome 21. Excess of these polypeptides results in a hydrophilic property of the dermis leading to nuchal fluid accumulation. However, why this should no longer happen after 14 weeks gestation is not known. Hyett et al. described the finding that in trisomy 21 fetuses a narrowing of the aortic isthmus below the 5th percentile is found in 49% of fetuses and that the degree of narrowing is greater in fetuses with high NT 17. Possibly narrowing of the aortic isthmus and widening of the ascending aorta lead to overperfusion of the head and neck region and to subcutaneous edema. The fact that with increasing gestation the diameter of the aortic isthmus increases more rapidly than the diameters of the aortic valve and distal ductus might explain the spontaneous resolution of NT at 14 weeks. In Turner syndrome, lymphatic dysplasia may account for the lymph accumulation in enlarged lymphatic sacs 18. However, increased NT is also associated with a variety of other fetal structural defects and genetic syndromes 15,19,20. A recent study suggests that the observed ultrasound feature of subcutaneous nuchal fluid collection may involve mesenchymal edema in the posterior part of the neck and distended jugular lymphatic sacs anterolaterally 21. A disturbed or delayed endothelial development of these enlarged lymphatic sacs may provide the link between increased nuchal fluid accumulation and cardiac dysfunction or maldevelopment as suggested by the frequent association of enlarged NT with abnormal ductus venosus flow and of cardiac defects Nuchal fluid accumulation has been observed in a variety of fetal defects suggesting different mechanisms ending in a common pathway. Assuming that in genetic, chromosomal or structural defects excessive nuchal fluid accumulation is the result of abnormal fetal development, one would expect persistence throughout the week period when all fetuses have some nuchal fluid 3. Normalization of the excessive fluid accumulation before 14 weeks gestation suggests a different underlying mechanism such as a developmental delay leading to a temporary cardiac dysfunction that is promptly overcome. If this were to be the case then it would not be surprising that fetuses in which normalization is documented at second measurement have a lower incidence of chromosomal abnormalities. Another possibility is that the observed phenomenon of disappearing enlargement in some fetuses reflects a fetus-specific pattern of nuchal enlargement. As described by Pajkrt et al. 3, most normal fetuses show a progressive increase and subsequent decrease in NT with advancing gestation, but the timing of the peak thickening seemed to be fetus-specific. In 6% of fetuses the first measurement was higher than at subsequent scanning, suggesting that the normal waxing phase had already passed. If similar fetus-specific patterns apply to fetuses with increased enlargement we could even speculate that the falsenegative cases, i.e. Down syndrome fetuses with normal NTs, may in fact have already had their moment of maximal nuchal enlargement at an earlier gestation. Clinical implications When screening for Down syndrome by NT repeat screening may lower the number of false-positives possibly at the cost of a slight decrease in sensitivity. However, several aspects of this concept of repeat screening have to be addressed. An ideal screening program should not only be able to detect as many affected individuals with minimal risk exposure, but also take into account aspects such us time span, efficiency, costs and acceptability when it comes to the global evaluation of its performance. Introduction of a repeat screening program in cases of an enlarged NT may diminish the advantage of early screening, as karyotyping would have to be postponed until after the second measurement.

6 174 Müller et al. Another problem lies in the fact that offering women with an abnormal NT a repeat scan might be confusing. It seems unlikely that women first receiving bad news would be adequately reassured if the second scan turned out to be normal. Withholding the first results until after the second scan as proposed in non-disclosure screening 26 is not an option because women would be selectively invited for a repeat scan only in the case of an abnormal result. Moreover, the residual percentage of chromosomal abnormalities in the present study in fetuses with disappearing enlargement was still 8%, which is higher than in a normal population and still warrants karyotyping. Furthermore, the risk of detecting additional developmental disorders in case of normal karyotype remains increased and therefore careful surveillance of these pregnancies is mandatory. Improvement of NT screening is more likely to come from simultaneous combination of NT with other markers, such as first-trimester serum screening 27 or, as has been proposed more recently, examination of the fetal nasal bone 28. Nevertheless, the phenomenon of the disappearing NT enlargement deserves attention not only for its clinical implications, but also as additional studies focused on this event may help in understanding the complex pathophysiological background of an excessive fluid accumulation in the fetal neck at weeks of gestation. REFERENCES 1. Nicolaides KH, Azar G, Byrne D, Mansur C, Marks K. Fetal nuchal translucency: ultrasound screening for chromosomal defects in first trimester of pregnancy. BMJ 1992; 304(6831): Snijders RJ, Noble P, Sebire N, Souka A, Nicolaides KH. UK multicentre project on assessment of risk of trisomy 21 by maternal age and fetal nuchal translucency thickness at weeks of gestation. Fetal Medicine Foundation First Trimester Screening Group. 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