Normal Nuchal Translucency Thickness Research Articles

The significance of rare chromosomal abnormalities and fetoplacental mosaicism in prenatal diagnosis in the non-invasive prenatal testing era

To determine the prevalence of microscopically visible de novo atypical chromosomal aberrations and fetoplacental mosaicism in a prenatal tertial referral center, and to investigate the maternal and fetal characteristics in connection with genomewide non-invasive prenatal screening. Retrospective cohort study from 2014 to 2019 of pregnancies with invasive genetic analysis. In the cohort of 2504 cases, the proportion of CVS was 53.3%. We diagnosed 200 chromosomal aberrations (8%), including 13.5% of de novo rare chromosomal aberrations (14 rare autosomal trisomies, 6 polyploidies, 5 structural aberrations and 2 small supernumerary marker chromosomes). The rate of fetoplacental mosaicism was 12.4%/77.8% in common/atypical chromosomal aberrations (p = 0.001) and confined to placenta in 17/40 cases. Associated ultrasound abnormalities were abnormal nuchal translucency and major malformations in 58% and 35% with common trisomies and 11% (p = 0.006) and 67% (p = 0.047) with true mosaic cases of rare abnormalities, respectively. Major ultrasound malformation was facial dysmorphism with rare aberrations. Potential application of genomewide non-invasive prenatal test in atypical chromosomal aberrations presumably would have been false-positive in 12 cases (44%), false-negative in 1 case (3.7%), and would have early detected 2 cases of rare autosomal trisomies (7.4%) without ultrasound anomalies. Structural ultrasound malformations with normal nuchal translucency thickness may be indicative of rare chromosomal aberrations. Application of genomewide non-invasive prenatal test is an alternative of early diagnostic methods with a potential of discordant results due to mosaicism. Knowledge about the presence of fetoplacental mosaicism influences risk estimation and genetic counseling, detailed cytogenetic characterization is of utmost importance. Orv Hetil. 2021; 162(29): 1156-1165.

Trials and tribulations of meta-analyzing procedure-related risks of amniocentesis and chorionic villus sampling.

Trials and tribulations of meta-analyzing procedure-related risks of amniocentesis and chorionic villus sampling.

Cardiac function in trisomy 21 fetuses

Trisomy 21 is associated with an increased nuchal translucency thickness (NT), abnormal ductus venosus (DV) flow at 11-14 weeks' gestation and congenital heart defects (CHD), and cardiac dysfunction has been hypothesized as the link between them. We therefore aimed to investigate whether cardiac function is altered in trisomy 21 fetuses. Between December 2003 and June 2009, we performed echocardiography on 46 trisomy 21 fetuses (28 with structurally normal heart and 18 with CHD) and on 191 chromosomally/phenotypically normal fetuses with a confirmed normal heart (87 with normal NT and 104 with NT ≥ 95(th) percentile), between 11 and 35 weeks' gestation. Measurements included: E- and A-wave peak velocity, E/A velocity ratio and E/time velocity integral (TVI) ratio over atrioventricular valves; myocardial performance index (MPI); semilunar valve peak velocity and acceleration time; stroke volume (SV); cardiac output; and DV pulsatility index for veins (PIV) at 11-14 weeks' gestation. Data were categorized into three different age groups for analysis (11 to 13 + 6, 14 to 21 + 6 and 22 to 35 weeks' gestation). The tricuspid valve (TV) A-wave velocity and aortic valve peak velocity were significantly reduced in trisomy 21 compared with normal fetuses. Other highly significant differences found in trisomy 21 fetuses at 11-14 weeks' were increased TV-E/A ratio and DV-PIV, and decreased pulmonary valve peak velocity. We also observed evidence of left ventricular (LV) systolic dysfunction, reduced SV and increased MPI. After 14 weeks' gestation, the mitral valve A-wave peak velocity and E/TVI ratio were significantly reduced in the trisomy 21 fetuses with normal hearts compared with the controls with increased NT. In comparison with controls with normal or increased NT, cardiac function in trisomy 21 fetuses is abnormal irrespective of the presence of CHD. Evidence for cardiac loading (increased preload and afterload) and LV systolic (in the first trimester) and later diastolic dysfunction was observed.

Distribution of Normal Nuchal Translucency Thickness: A Multicenter Study in Thailand

Aims: To establish the normative data distribution of nuchal translucency (NT) thickness in Thai fetuses. Methods: A cross-sectional multicenter study was conducted among 6,455 women with singleton pregnancies and gestational age between 10 and 14 weeks. For each case, the fetal crown-rump length (CRL) and NT were measured by transabdominal ultrasound. Transvaginal ultrasounds were used in poorly visualized cases. The distribution values of the NT thicknesses and their corresponding 10-mm CRL intervals between 45 and 84 mm were examined to obtain the median and 95th percentiles. Quantile regression modeling across the CRLs was performed to obtain the reference values. Results: Transabdominal ultrasound measurements were successfully done on 6,347 fetuses with 39 cases by the transvaginal route. Fetuses with CRL between 45 and 84 mm and normal outcomes made up a total of 4,352 cases. The mean (SD) gestational age, CRL and NT thickness were 12.5 (0.7) weeks, 60.2 (9.7) mm, and 1.15 (0.38) mm, respectively. The mean normal NT increased linearly with CRL. The quantile regression equation to predict the 95th percentile of the NT thickness (mm) was 0.727 + [0.017 × CRL (mm)]. Conclusions: The NT thickness in normal Thai fetuses was found to be thinner than in both Caucasian and other Asian populations.

Umbilical vein anomaly in fetuses with Down syndrome

To describe the prevalence of abnormal umbilical vein (UV) anatomy in fetuses with Down syndrome. This was a retrospective survey covering a 24-month period of fetuses with a genetic diagnosis of Down syndrome following a routine early second-trimester (12-16-week) detailed fetal anomaly scan at a single academic tertiary referral center. In our unit this exam includes fetal umbilicoportal venous system evaluation. During the study period, 37 fetuses were diagnosed with Down syndrome and had a detailed early anatomy scan. In four (11%) the detailed early anomaly scan revealed that the UV was connected to the hepatic portion of the inferior vena cava (IVC) at a position lower than its usual site. Their average gestational age at diagnosis was 13 + 6 (range, 11 + 6 to 15 + 2) weeks. Three of the four fetuses had a nuchal translucency thickness of 3-4 mm. In one fetus there was an additional finding of significant tricuspid regurgitation and the one with normal nuchal translucency thickness had an atrioventricular septal defect (atrioventricular canal) and umbilical cord hernia. During the same period three of 2500 (0.12%) fetuses with normal karyotype demonstrated similar anomalous insertion of the UV into the IVC, creating a portocaval shunt which had normal ductus venosus-like Doppler flow in all three cases. The odds ratio for abnormal umbilicoportal venous system in fetuses with Down syndrome compared with the normal population was 107.4 (95% CI, 19.2-637.1). Fetuses with Down syndrome demonstrate an increased prevalence of abnormal connection of the UV to the IVC.

Abnormal first‐trimester ductus venosus blood flow: a marker of cardiac defects in fetuses with normal karyotype and nuchal translucency

To evaluate the independent contribution of ductus venosus (DV) blood flow assessment at 11-14 weeks' gestation to the prediction of congenital heart defects (CHD) in chromosomally normal fetuses, irrespective of the value of the nuchal translucency thickness (NT). During a 4-year period, all singleton pregnancies from 11 + 0 to 13 + 6 weeks' gestation were scanned for NT and DV blood flow in a tertiary center. Abnormal DV blood flow was defined as either absent or reversed flow during atrial contraction (AR-DV). Fetal echocardiography was performed in all cases with either NT > 99(th) percentile or AR-DV. Follow-up was assessed by postnatal examination or autopsy in cases of termination of pregnancy or perinatal death. A total of 6120 pregnancies were scanned at a median gestational age of 12 weeks, and 45 cases of CHD were detected. AR-DV was found in 206 fetuses, of which 145 (70.4%) had a normal karyotype. Among fetuses with AR-DV and normal karyotype, 11 cases of CHD were diagnosed, giving a sensitivity of 24.4%, a positive predictive value of 7.6% and an odds ratio of 9.8. Increased NT (> 99(th) centile) was present in 55 of the 145 (37.9%) cases with AR-DV and normal karyotype, and in 6/11 (54.5%) of those with CHD. Thus, the group of 90 fetuses with abnormal DV blood flow and normal NT contained five cases of CHD, for a sensitivity of 11.1%, a positive predictive value of 5.5% and an odds ratio of 8.5. Right-heart anomalies were predominant in those cases with isolated AR-DV (4/5), but no specific CHD pattern was found in those with increased NT. The detection rate of CHD by the combined use of increased NT and/or AR-DV in the first trimester improved from 28.9% (13/45) to 40.0% (18/45). In experienced hands, abnormal DV blood flow in the first trimester is an independent predictor of CHD and should constitute an indication for early echocardiography. In this study, the use of DV blood flow assessment increased early detection of CHD by 11% with respect to the use of NT measurement alone.

Jugular lymphatic sacs in first‐trimester fetuses with normal nuchal translucency

To assess the ultrasonographic appearance of the jugular lymphatic sacs (JLS) in first-trimester fetuses with a normal nuchal translucency (NT). Seventy-five fetuses with a normal NT thickness (< 95(th) percentile) were examined weekly between 11 and 17 weeks of gestation. After measurement of the NT thickness, the neck region was examined using both transvaginal and transabdominal ultrasonography for the presence of JLS. If present, their dimensions were measured in three directions and the volume was calculated using the formula for a spheroid. Data were analyzed using multilevel analysis. Seventy-five fetuses were evaluated and a total of 243 ultrasound examinations of the neck region were performed. In 25 (33%) of the 75 fetuses, the JLS could be observed once or more than once. In 19 fetuses JLS were visualized once, in five fetuses twice and in one fetus three times. In total, the JLS were visualized 32 times (n = 15 bilaterally, n = 15 only the left JLS and n = 2 only the right JLS). Relatively greater NT thickness was associated with a higher probability of the presence of JLS, although this was not statistically significant (NT < 1 mm, probability 0.07; NT 1-2 mm, probability 0.15, P = 0.10; NT > 2 mm, probability 0.20, P = 0.08). Gestational age was predictive for the presence of JLS, with the highest probability between 13 and 15 weeks of gestation (P < 0.01). No relationship was found between gestational age and the volumes of the left and right JLS. The JLS can be visualized on ultrasound examination in a significant proportion of fetuses with normal NT, most often between 13 and 15 weeks of gestation, and this does not seem to be associated with any abnormality in these fetuses.

Perinatal Imaging in Bronchopulmonary Sequestration

Received September 2, 2008, from the Fetal Medicine Center, Department of Obstetrics and Gynecology, Clinica Las Condes, Santiago, Chile. Revision requested September 8, 2008. Revised manuscript accepted for publication October 7, 2008. I thank Ximena Ortega, MD, for evaluating the prenatal magnetic resonance imaging; Jose M. Cortes, MT, and Juan A. Escaffi, MD, for performing and evaluating the angiographic computed tomography; and Angel Blanco, MD, Jose L. Martinez, MD, and Hernan Villalon, MD, for their substantial contribution to the postnatal care of the infant reported here. This work was supported by the Sociedad Profesional de Medicina Fetal “Fetalmed” Limitada, Chile. Address correspondence to Waldo Sepulveda, MD, Fetal Medicine Center, Clinica Las Condes, Casilla 208, Santiago 20, Chile. E-mail fetalmed@yahoo.com Abbreviations CCAM, cystic congenital adenomatoid malformation; CT, computed tomography; MRI, magnetic resonance imaging 30-year-old woman, gravida 2, para 1, was referred to our center at 21 weeks’ gestation after the prenatal detection of an echogenic mass in the right lung during a second-trimester anatomy scan. Her medical and obstetric histories were unremarkable; the current pregnancy had been otherwise uncomplicated; and the first-trimester scan at 11 weeks confirmed the dates and a normal nuchal translucency thickness measurement. Sonographic examination at referral showed adequate fetal growth and a normal amniotic fluid volume. Detailed examination of the fetal anatomy revealed a predominantly solid echogenic lesion with several small cysts, the largest measuring 3 mm, occupying the lower two-thirds of the right lung (Figure 1, A and B). There were no signs of a mediastinal shift, cardiac compression, abnormal venous return, or additional fetal structural anomalies. Color Doppler sonography depicted a large arterial vessel feeding the mass, which originated from the abdominal aorta (Figure 1C). The diagnosis of pulmonary sequestration was entertained, but the presence of small cysts within the mass also suggested a hybrid lesion associated with cystic congenital adenomatoid malformation (CCAM) of the lung. The pregnancy was followed with serial scans, which showed a slight reduction of the size of the mass, a normal amniotic fluid volume, and no signs of fetal hydrops. Fetal magnetic resonance imaging (MRI), performed at 31 weeks, confirmed the presence of a predominantly solid mass with small cysts in the fetal right lung and a feeding vessel arising from the abdominal aorta and crossing the diaphragm (Figure 2). At 38 weeks, a male neonate was delivered vaginally, weighing 3200 g and with Apgar scores of 9 and 10 at 1 and 5 minutes, respectively. There were no neonatal respiratory complications and the infant remained asymptomatic. Angiographic computed tomography (CT) was per-

Congenital diaphragmatic hernia in a first‐trimester ultrasound aneuploidy screening program

To review our experience with the prenatal detection of congenital diaphragmatic hernia (CDH) in fetuses presenting for ultrasound screening of chromosomal abnormalities in the first trimester. As part of our first-trimester ultrasound protocol, fetuses with a crown-rump length between 45 and 84 mm underwent a limited anatomical assessment in conjunction with nuchal translucency thickness measurement and nasal bone assessment. Cases of CDH diagnosed prenatally or after delivery in this population were identified. Among the six cases of CDH detected (prevalence of 1 in 927), the first-trimester ultrasound findings were abnormal in five fetuses (83%), including three with increased nuchal translucency only; one with increased nuchal translucency, an intrathoracic stomach, dextrocardia and a cephalocele; and one with normal nuchal translucency thickness and a small, complex intrathoracic mass later confirmed as the fetal stomach. The diagnosis of CDH was confidently made in the first trimester in one case, in the second trimester in three cases, and after birth in the remaining two cases. The diagnosis of CDH in the first trimester is difficult, especially in those cases in which the defect is small or late migration of the abdominal viscera occurs. Therefore, screening for CDH in the first trimester is unlikely to be effective.

P31.09: Absent nasal bone with normal nuchal translucency thickness at 11–14 weeks in trisomy 21

P31.09: Absent nasal bone with normal nuchal translucency thickness at 11–14 weeks in trisomy 21

Abnormal first‐trimester ductus venosus blood flow: a risk factor for adverse outcome in fetuses with normal nuchal translucency

First-trimester nuchal translucency thickness (NT) is a potent tool for assessment of fetal risks of aneuploidy and other adverse outcomes. When NT is increased, Doppler assessment of the ductus venosus (DV) enhances the prediction specificity for Down syndrome. This study assessed abnormal Doppler DV waveform as a predictor of adverse outcome when the NT is normal. This was a case-control study of 2,505 consecutive patients undergoing NT screening in our certified first-trimester screening program. First-trimester Doppler assessment of DV was performed and atrial systolic velocity was rated as antegrade (normal) or absent/reversed (DV-RAV; abnormal). Each case with normal NT (< 95(th) percentile) and DV-RAV was matched with two controls with respect to maternal age within 1 year, NT within 0.2 mm, crown-rump length within 3 mm, and closest calculated aneuploidy risk. Outcomes for paired variables were compared using t-test and Chi-square test. Forty-seven (1.9%) patients had normal NT and DV-RAV. After exclusion of three cases with obvious first-trimester anomalies and two with incomplete outcome data, 42 remained for analysis. Adverse outcome included cardiovascular defects (n = 6), fetal growth restriction (n = 3), renal anomaly (n = 2), aneuploidy (n = 3) and multiple defects (n = 3), in a total of 11/42 cases (26.2%). Cardiac abnormalities, renal abnormalities and perinatal death were all significantly more common in the study group (all P < 0.05). Abnormal first-trimester DV Doppler findings appear to predict adverse outcome independently of a normal NT. These patients need detailed mid-trimester assessment of fetal anatomy with formal echocardiography, and subsequent follow-up.

P01.40: Prenatal diagnosis of trisomy 21 in a fetus with normal nuchal translucency thickness and reversed end‐diastolic ductus venosus flow

P01.40: Prenatal diagnosis of trisomy 21 in a fetus with normal nuchal translucency thickness and reversed end‐diastolic ductus venosus flow

Increased nuchal translucency and distended jugular lymphatic sacs on first‐trimester ultrasound

To investigate the presence and volume of jugular lymphatic sacs (JLS) in first-trimester fetuses with normal nuchal translucency thickness (NT) and in those with increased NT. This was a prospective study of 26 fetuses with NT > 95(th) percentile, which were compared with 137 fetuses with normal NT. Following crown-rump length (CRL) and NT measurement the neck region of the fetus was studied by transvaginal ultrasound. The JLS presented as spheroidal translusencies in the anterolateral region of the neck. The prevalence of JLS differed significantly between fetuses with enlarged NT and the control group (P < 0.0001). In the group of 26 fetuses with increased NT, 22 had clearly visible JLS. Chorionic villus sampling revealed aneuploidy in 10 and euploidy in 16 fetuses. In the control group two fetuses, with NT values of 2.8 mm and 2.9 mm, had JLS; pregnancy outcome was normal in both cases. Logistic regression analysis in the total study group showed that an increase in NT was associated with a greater probability of JLS being present (for NT = 3-3.5 mm, probability = 0.67; for NT > 3.5 mm, probability = 0.93). In fetuses with JLS, an increase in CRL was associated with a significant increase in right JLS volume (r = 0.51; P-value = 0.01) and a non-significant increase in left sac volume (r = 0.40; P-value = 0.09). Increase in NT was not associated with a significant increase in JLS volume. There is a significant association between increased NT and the presence of JLS on first-trimester ultrasound. In our opinion, the pathophysiological explanation for increased NT lies in a disturbance in lymphangiogenesis.

First‐trimester fetuses with increased nuchal translucency do not show altered intracardiac flow velocities

To study intracardiac flow velocities in first-trimester fetuses with normal nuchal translucency thickness (NT) and those with increased NT. Ultrasound examinations were performed in 85 normal fetuses and 45 fetuses with NT > 95(th) percentile. Follow-up was complete and postmortem examination was performed on terminated pregnancies. Flow velocities during the early (e-wave) and late (a-wave) peaks across the tricuspid and mitral valves were measured and compared, using multilevel analysis, between the fetuses with normal and those with increased NT. In the group with increased NT, fetuses with and without a heart defect irrespective of the karyotype were compared, and in this group, euploid and aneuploid fetuses were compared, irrespective of the presence of a heart defect. No difference in intracardiac flow velocities was found between fetuses with normal and those with increased NT. Within the group of fetuses with increased NT, there was no difference between the fetuses with and without a cardiac defect. However, comparison of aneuploid with euploid fetuses within the group with increased NT showed that both the e-wave and a-wave peaks were decreased significantly by 3.03 cm/s and 5.95 cm/s, respectively, across the tricuspid valve, and by 3.47 cm/s and 5.92 cm/s, respectively, across the mitral valve (P < 0.05). The most common cardiac malformations were septal defects. There is no difference in intracardiac blood flow velocities between normal fetuses and those with increased NT. This contradicts the theory that NT is caused by impaired atrial contraction or cardiac failure. In fetuses with increased NT, those with aneuploidy show a decreased e-wave and a-wave compared with euploid fetuses. This cannot, however, be explained by the presence of cardiac defects, because there is no difference between fetuses with and without a cardiac defect. Therefore, we hypothesize that the relationship between enlarged NT and cardiac defects can only be explained by a developmental process that coexists at this period of gestation and is linked to cardiovascular development.

Ductus venosus blood flow assessment at 11 to 14 weeks of gestation and fetal outcome.

To evaluate the association between abnormal ductus venosus (DV) at 11-14 weeks' gestation and chromosomal abnormalities, structural defects and fetal outcome. DV flow-velocity waveform (DV-FVW) and nuchal translucency thickness (NT) were prospectively evaluated in 1217 singleton pregnancies. The DV-FVW was abnormal in 84 fetuses, NT was above the 95th centile in 160 fetuses and both markers were observed in 41 fetuses. Chromosomal defects were diagnosed in 22 fetuses. The sensitivity, specificity and positive and negative predictive values for an abnormal karyotype were 86.4%, 86.9%, 11.9% and 99.7%, respectively, for an increased NT. These values were 68.2%, 96.9%, 31.3% and 99.3%, respectively, for DV-FVW abnormalities and 68.2%, 97.6%, 36.6% and 99.3%, respectively, when both markers were found simultaneously. Regarding structural defects, these values were 43.8%, 92.9%, 8.3% and 99.1% for an abnormal NT, 25.0%, 92.6%, 4.8% and 98.8% for DV-FVW abnormalities and 25.0%, 97.9%, 15.4% and 98.9% for both together. Considering those cases of unexplained fetal demise, the values were 44.4%, 85.9%, 5.0% and 98.9% for NT abnormalities, 22.2%, 92.6%, 4.8% and 98.6% for an abnormal DV-FVW and 22.2%, 98%, 15.4% and 98.7% for both. In cases with increased NT, the percentage of live births with normal karyotype and no major fetal structural defects decreased from 93.8% in normal DV-FVW fetuses to 77.3% in abnormal ones. DV assessment at 11-14 weeks' gestation is useful in screening for fetal chromosomal abnormalities and may help to reduce the false-positive rate when combined with NT measurement. Abnormal DV-FVW is also associated with an increase in adverse perinatal outcome in fetuses with enlarged NT. However, the value of DV-FVW assessment in cases with normal NT is unclear.

Nuchal translucency thickness and outcome in chromosome translocation diagnosed in the first trimester

In order to determine the significance of nuchal translucency thickness on the subsequent natural history of first-trimester fetuses with a chromosome translocation, seven consecutive cases diagnosed between 11 and 13 weeks of gestation were reviewed. Nuchal translucency measurements were successfully obtained before chorionic villus sampling (CVS) in all cases. Three fetuses had an unbalanced translocation and all were associated with increased nuchal translucency and multiple anomalies at the detailed second-trimester scan. There were no survivors in this group. The remaining four fetuses had a balanced translocation; all had normal nuchal translucency thickness and no structural anomalies were detected in the second trimester. Three of these fetuses were born at ≥35 weeks of gestation and were phenotypically normal. However, an unexpected single fetal demise occurred in a dichorionic twin pregnancy at 28 weeks of gestation. It is concluded that nuchal translucency measurements provide important prognostic information on pregnancy outcome in first-trimester fetuses with a chromosome translocation. In parents with a known balanced translocation, the detection of increased nuchal translucency at 11–14 weeks of gestation is associated with unbalanced translocations, structural anomalies and poor pregnancy outcome. Copyright © 2001 John Wiley & Sons, Ltd.

Nuchal translucency thickness and outcome in chromosome translocation diagnosed in the first trimester

In order to determine the significance of nuchal translucency thickness on the subsequent natural history of first-trimester fetuses with a chromosome translocation, seven consecutive cases diagnosed between 11 and 13 weeks of gestation were reviewed. Nuchal translucency measurements were successfully obtained before chorionic villus sampling (CVS) in all cases. Three fetuses had an unbalanced translocation and all were associated with increased nuchal translucency and multiple anomalies at the detailed second-trimester scan. There were no survivors in this group. The remaining four fetuses had a balanced translocation; all had normal nuchal translucency thickness and no structural anomalies were detected in the second trimester. Three of these fetuses were born at > or =35 weeks of gestation and were phenotypically normal. However, an unexpected single fetal demise occurred in a dichorionic twin pregnancy at 28 weeks of gestation. It is concluded that nuchal translucency measurements provide important prognostic information on pregnancy outcome in first-trimester fetuses with a chromosome translocation. In parents with a known balanced translocation, the detection of increased nuchal translucency at 11-14 weeks of gestation is associated with unbalanced translocations, structural anomalies and poor pregnancy outcome.

Prenatal diagnosis of mosaic trisomy 8 in a fetus with normal nuchal translucency thickness and reversed end‐diastolic ductus venosus flow

We report a case of the prenatal diagnosis of trisomy 8 in a fetus presenting with normal nuchal translucency of 0.8 mm and reversed end-diastolic ductus venosus blood flow at a routine first-trimester scan at 11 weeks of gestation. No structural abnormalities were detected by the ultrasound scan. Karyotyping by chorionic villus sampling led to the diagnosis of mosaic trisomy 8, which was confirmed by fluorescent in-situ hybridization on fetal tissue samples.

First trimester diagnosis of monoamniotic twin pregnancies.

This study reports the ultrasound findings and pregnancy outcome for a series of monoamniotic twin pregnancies diagnosed at 11-14 weeks' gestation. Of 315 monochorionic twin pregnancies examined, there were 12 (3.8%) monoamniotic, including four sets of conjoined twins (1.3%). The parents opted for termination of pregnancy in all cases of conjoined twins. In four other cases, there was discordancy for major structural fetal abnormality (kyphoscoliosis, anencephaly, body stalk defect, diaphragmatic hernia), and the cotwin was structurally normal. In the four cases in which both twins were structurally normal, ultrasound examination demonstrated normal nuchal translucency thickness in all cases but cord entanglement was demonstrated from the first trimester. Two cases were managed expectantly; one resulted in livebirth of both twins at 31 weeks' gestation and the second in intrauterine death of both fetuses at 21 weeks. Two pregnancies were treated with Sulindac; one resulted in a single intrauterine death at 30 weeks and delivery of a normal cotwin, the other, in intrauterine death of both fetuses at 31 weeks'. Monoamniotic twin pregnancies are associated with a high risk of fetal abnormalities and perinatal death and the mortality rate is higher than previously reported from series with recruitment later in gestation.