All five digits of the hands of fetuses with Down syndrome are short.

OBJECTIVE: To compare mid-gestation sonographic measurements of all five digits of the hands of fetuses with Down syndrome with those of normal controls. METHODS: Twenty-nine fetuses between 17 and 26 weeks' gestation which had been confirmed by karyotyping to have Down syndrome were included in this prospective study. Each fetus was scanned once and the digits of only one hand were measured. Measurements were compared with those of 302 previously reported normal controls matched for gestational age. All measurements were expressed in multiples of the gestation-specific normal median (MoM) for each digit. RESULTS: Compared to 1 MoM for the length of Digits 1 to 5 from the normal population, the respective values in the Down syndrome digits were: 0.94, 0.85, 0.92, 0.88 and 0.85 MoM, representing values significantly lower than normal (P < 0.05; t-test). CONCLUSIONS: All five digits of the hands of fetuses with Down syndrome are shorter than are those of euploid fetuses. Integration of fetal digit measurement into the antenatal assessment of selected high-risk cases may be of value although confirmation of our findings should be obtained before this measurement is incorporated into Down syndrome screening in the general population.

Comparison of pregnancy outcome of euploid fetuses with increased nuchal translucency (NT) expressed in NT MoM or delta-NT.

OBJECTIVE: To evaluate the outcome of euploid fetuses with increased nuchal translucency thickness (NT) expressed in multiples of the median (MoM) or delta-NT. METHODS: Included in the study were euploid fetuses with increased NT >or= 95(th) centile, for which information about pregnancy outcome was available. The following parameters were defined as an adverse outcome: miscarriage, structural anomalies justifying termination of pregnancy, and structural anomalies, genetic syndromes and neurodevelopmental problems diagnosed postnatally. Fetal outcome according to NT MoM and delta-NT was calculated using different cut-off values. Calculations of the odds ratio for adverse outcome were performed using either NT MoM or delta-NT as a predictor in logistic regression models. RESULTS: The study comprised 168 euploid fetuses. Of these, 38 (23%) had an adverse outcome: 11 (6%) had miscarriages, 14 (8%) were terminated because of fetal abnormalities detected on the prenatal scan and 13 (7%) were found postnatally to have abnormalities. The incidence of cases exhibiting an adverse outcome was 5.3%, 19.2% and 58.5% for NT values of 1.6-1.9, 2.0-3.0 and >3.0 MoM, respectively (P < 0.0001, chi(2) test), and 3.9%, 16.7% and 62.8% for delta-NT values of 1.0-1.4, 1.5-2.5 and >2.5 mm, respectively (P < 0.0001, chi(2) test). Using cut-offs of 2.0 MoM and delta-NT of 1.5 mm, the odds ratios for adverse outcome were 10.2 (95% CI, 3.4-30.4) and 15.4 (95% CI, 4.2-43.6), respectively. CONCLUSION: Both the NT MoM and delta-NT approaches may be used to determine cases which require additional antenatal investigation as well as fetal karyotyping. For this purpose we suggest using a cut-off of either 2.0 MoM or a delta-NT of 1.5 mm.

A model for disclosing the first trimester part of an integrated Down's syndrome screening test.

This study was designed to evaluate a model for disclosing the first part of an integrated Down's syndrome (DS) test without affecting its low false-positive results. Parturient women underwent sequential DS-screening tests. They included nuchal translucency (NT) and biochemistry assessments in the first trimester and a mid-gestation triple test. Although screening tests results were given following each test, fetal karyotyping was performed by means of mid-gestation amniocentesis. The proposed approach for disclosure refers to either (a) cases picked by a statistical model (this is based on a logistic regression analysis and a receiver-operated curve that was set to a specificity of 100% of first-trimester markers pointing on at very high probability of aneuploidy) or (b) cases demonstrating a first trimester DS risk > or = 1 : 40 (a threshold level at which the integrated test results will always be screen positive). The results of the sequential screening and pregnancy outcome were available for 372 normal and 22 chromosomal affected singletons. NT and pregnancy-associated placental protein A emerged as the most sensitive marker combination. The statistical model picked up seven of 22 abnormal cases (32%), and a first-trimester DS risk > or = 1 : 40 was detected in 11 (50%) (there was an overlap of five cases). The combined strategy yields a 60% detection rate (13/22) of the affected pregnancies and without any increase in the false-positive results. This can be achieved immediately following the first part of the integrated DS test. This model obviates the ethical, clinical, and financial implications of further assessing about 60% of the affected pregnancies.

Bedside estimation of Down syndrome risk during first-trimester ultrasound screening.

OBJECTIVE: To construct tables for 'bedside' estimation of Down syndrome risk based on maternal age and nuchal translucency measurements. METHODS: Likelihood ratios were calculated using the log multiple of median Gaussian model. The parameters for the model (mean and standard deviation) were derived from 5560 normal and 51 Down syndrome-affected pregnancies scanned during the first trimester in three different centers. Equations for calculating maternal background risk and median values were obtained from previous reports. The results were compared to two modalities using the log Gaussian model and software that uses the delta-value model. RESULTS: The distribution fitted the data well, and the parameters obtained in the study group for the log multiple of median model were a mean of 0 and a standard deviation of 0.12356 among normal pregnancies and a mean of 0.305312 and a standard deviation of 0.240337 among Down syndrome-affected ones. The likelihood ratios obtained for the various combinations of fetal crown-rump lengths and nuchal translucency measurements were comparable to other modalities reported earlier. CONCLUSIONS: The results of the current study provide useful tables for simple and accurate 'bedside' estimation of Down syndrome risk without the need for computerized software or complicated calculations.

Nuchal translucency measurements in consecutive normal pregnancies. Is there a predisposition to increased levels?

OBJECTIVE: The current study aims to assess the relative risk of isolated increased nuchal translucency (NT) in consecutive normal pregnancies. METHODS: A retrospective search of the fetal medicine unit database in which NT assessment was conducted. Only singleton fetuses with an unremarkable pregnancy outcome were included in this study. The repeated NT either at a threshold of >2.5 mm or > or =95th centile of the normal range for various CRLs (2 mm at a CRL < or =44 mm to 2.85 mm at CRLs 83-84 mm) was assessed. Pearson's correlation was applied to investigate any correlation between a log(10) NT obtained in two consecutive pregnancies. The chance of an increased NT in the first pregnancy followed by similar results in the subsequent one was assessed using Fisher's exact test. RESULTS: Ninety-two pregnant women with two consecutive normal pregnancies were identified. There was a highly significant correlation between the log(10) NT values measured in the consecutive pregnancies (r = 0.38; p < 0.001). The relative risk of an isolated NT > or =2.5 mm in the first pregnancy to be followed by a similar finding in the subsequent one was 18.21 (95% confidence interval [CI]: 3.62-91.55). The relative risk of an isolated NT > or =95th centile in the first pregnancy to be followed by a similar result in the subsequent one was 21 (95% CI: 4.53-97.44). CONCLUSION: The current results indicate a significant correlation of NT values in consecutive unaffected pregnancies. There also was a predisposition for a repeated isolated increased NT in subsequent pregnancies. Additional series and more information are needed before firm conclusions can be made.

Prenatal age-specific reference intervals for measuring all five digits of the fetal hand.

OBJECTIVE: To construct prenatal age-specific reference intervals for measurement of five digits in normal fetuses. PATIENTS AND METHODS: Prospective cross-sectional study of fetuses assessed at an antenatal ultrasound unit in a university-affiliated general hospital. The study cohort comprised 302 pregnant women attending our clinic for routine fetal biometry or anomaly scan between December 1997 and June 2000. They all fulfilled the study inclusion criteria: singleton fetuses with normal anatomy, accurate gestational age and no medical complications of pregnancy. Each fetus was scanned once only and the finger measurements of one hand were obtained. Electronic calipers were placed on the outer margin of the proximal phalanx to the outer margin of the distal phalanx level. Those measurements and the relevant gestational age were registered in a computerized database. RESULTS: The linear increase of size of each of the five fingers was plotted across the evaluated range of gestation (P < 0.001; r2 between 0.85 and 0.86 for fingers I to V). Tables showing the 5th, 50th and 95th centiles of finger lengths between 14 and 27 weeks' gestation were created based on the reference interval charts. CONCLUSIONS: Second-trimester measurement of all five digits of the fetal hand is feasible. This may assist in the evaluation of fetuses that are primarily suspected of having genetic abnormalities that might be expressed by deviation in finger length.

Nuchal translucency measurement and pregnancy outcome after assisted conception versus spontaneously conceived twins.

BACKGROUND: Nuchal translucency (NT) measurement for Down's syndrome screening or detecting various fetal anomalies is a reliable sonographic marker. This study evaluates the contribution of NT screening in spontaneously conceived and assisted conception twin pregnancies. METHODS AND RESULTS: Maternal age at measurement, chorionicity, ultrasound features, karyotype results and pregnancy outcome were recorded prospectively and compared in 83 assisted reproduction treatment and 91 spontaneously conceived twins. Pregnancy outcome was evaluated according to maternal age, method of conception, NT data and chorionicity. NT measurements (> or =95 centiles of the normal range) were considered screen-positive and mid-pregnancy fetal karyotyping was advised. Complicated pregnancy outcome, which could be signalled by increased NT, was defined as either chromosomal abnormalities, severe structural defects or fetal demise. Based on NT measurements, 16 fetuses (4.6%) were found to be screen-positive. Five of them had chromosomal aneuploidy and selective termination was performed. The parents also opted for this procedure in another five fetuses because of major structural abnormality diagnosed during NT assessment. No other chromosomal or major fetal abnormality were found post-natally. Although no difference was found in NT, crown-rump length and maternal age between spontaneous and assisted reproduction technology twin pregnancies, the former group had a significantly higher rate of screen-positive results (7 versus 2%, P = 0.047), amniocentesis uptake (33 versus 22%, P = 0.014), monochorionic twining (32 versus 4%, P = 0.001) and complicated pregnancy outcome (11 versus 5%, P = 0.02). CONCLUSION: The present study confirms that first trimester target scanning can improve outcome by early detection and management of cases with an anomalous co-twin. It also identifies some differences between spontaneously and artificially conceived twin pregnancies in relation to this area of testing.

[Prenatal Down's syndrome screening at 10-14 weeks gestation using the combined nuchal translucency and maternal serum biochemistry: preliminary results of the first 358 cases].

We report our preliminary experience of prenatal screening for Down's syndrome (DS) using nuchal translucency (NT) measurement combined with the serum biochemistry analysis of Free beta-human chorionic gonadotropin (F beta hCG) and pregnancy associated plasma protein A (PAPP-A) all measurement at 10-14 weeks of gestation. Of the 358 parturient women which enrolled in the study, 9 cases were not included because of fetal anomalies or miscarriages. Thus the study group included 349 singleton pregnancies in which complete prenatal and infant follow-up was available. Forty-four pregnant women were found to be screen positive (12.6%) and in 13 cases (27%) of them fetal chromosomal aneuploidies were diagnosed. Looking into the markers profile we found that the NT was a sensitive marker which was abnormally increased in all the fetal aneuploidies. Serum F beta hCG was found to be a promising marker as well, being significantly elevated (2.26 +/- 0.86 multiple of the medians, MoM) in DS cases, and decreased (< 0.5 MoM) in two cases of Edward's syndrome. On the contrary, PAPP-A was found less sensitive, and its mean MoM values were not significantly different between DS versus euploid fetuses. Our preliminary results support the promising success of DS screening using NT and F beta hCG.

Does a 'notched' nuchal translucency indicate Down syndrome fetuses or other adverse pregnancy outcome?

The aim of the present study was to assess the sonographic contour of the increased nuchal translucency (NT) and to correlate this with pregnancy outcome. Fifty sonographic images of fetuses with increased NT [> 95th centile thickness of the normal range for crown-rump length (CRL) between 38 and 84 mm] were retrospectively assessed. In all the cases a complete pregnancy and even infancy follow-up (< 36 months) was available. The NT appearances were subdivided into two forms: a 'notched' or 'uniform' appearance. The images were correlated with karyotype results [trisomy 21 (DS) vs euploid cases] and pregnancy outcome. Complicated outcomes were classified as being either DS fetuses, miscarriage or termination of pregnancy because of structural anomaly. Thus 30/35 (86%) of the euploid fetuses had a 'uniformly' increased NT, whereas 8/13 DS cases (62%) had a 'notched' appearance (Fisher's exact test, p = 0.004). Additionally, 27/29 fetuses (93%) which had an uneventful pregnancy outcome had a 'uniform' increased NT, whereas 12/26 (57%) of the fetuses which had adverse pregnancy outcome had a 'notched' appearance of their NT (Fisher's exact test, p < 0.001). Although it was not possible to correlate the sonographic data with post-evacuation microdissection findings, it is possible that a uniformly shaped, increased NT may be more representative of a developmental delay in a normal fetus. Conversely, a 'notched' nuchal surface may represent abnormal lymphatic or cardiovascular development more commonly seen in DS fetuses.

Reconstructed measurements produced from ultrasound images using a computerized system.

OBJECTIVE: The aim of this study was to evaluate the feasibility and accuracy of reconstructed measurements produced from video-printed ultrasound images. DESIGN: Reproduction of reconstructed measurements using designated software and comparison of the results with regular measurements derived from the same images. SUBJECTS: Seventy regular sonographic examinations of biparietal diameter (BPD) and nuchal translucency (NT) thickness. METHODS: The study included 35 conventional-size (BPD) and 35 small-size (NT) measurements. Each image was measured twice during a dynamic ultrasound examination (regular measurements) and twice using a computerized system (reconstructed measurements). The latter comprised three steps: (i) computerization (computer-generated images by scanning); (ii) calibration (using the scale located alongside the image); (iii) measurement (placing the calipers at the desired points). RESULTS: All images were successfully scanned, and the computer-generated images were of sufficient quality for proper measurement. There was no difference between mean values of regular and reconstructed BPD measurements, 63.9 mm (3.7 mm, SE) and 63.6 mm (3.8 mm, SE), respectively. Similarly, mean values of regular NT measurements were similar to the reconstructed ones, 1.48 mm (0.09 mm, SE) and 1.49 mm (0.09 mm, SE), respectively. Repeated regular BPD and NT measurements exhibited repeatability coefficients of 1.6 mm and 0.4 mm, respectively. These values were smaller than those obtained by repeated reconstructed measurements of 2.1 mm and 0.52 mm, respectively. CONCLUSIONS: Reconstructed measurements of ultrasound video-printed images are feasible, require modest facilities and exhibit more than reasonable accuracy. This option may contribute to medical research, audit, quality control and training, as well as to medico-legal issues.

Three-dimensional vaginal sonography in obstetrics and gynaecology.

Great strides have recently been made in obstetrics and gynaecology secondary to the development of high-performance transvaginal ultrasound (TVS) instruments. However, even this advanced technology can provide only two-dimensional (2D) views of three-dimensional (3D) structures. Although an experienced examiner can easily piece together sequential 2D planes for creating a mental 3D image, individual sectional planes cannot be achieved in a 2D image because of various difficulties. Today, 3D TVS can portray not only individual image planes, it can also store complex tissue volumes which can be digitally manipulated to display a multiplanar view, allowing a systematic tomographic survey of any particular field of interest. The same technology can also display surface rendering and transparency views to provide a more realistic 3D portrayal of various structures and anomalies. The current review provides examples and discussions of the various applications in obstetrics, gynaecology and assisted reproduction in which 3D TVS is a useful supplement to image modality.

Combined first trimester nuchal translucency and second trimester biochemical screening tests among normal pregnancies.

We prospectively examined whether first trimester nuchal translucency (NT) and second trimester triple test (TT) results are correlated, and determined overlapping and mutual screen-positive rates. Results of NT, TT, amniocentesis and pregnancy outcome were obtained in 508 normal pregnancies. Inter-test correlation was performed by comparing the likelihood ratios (LR). Overlapping of screen-positive cases, of NT and TT, was determined by comparing mutual risks for Down syndrome (DS) livebirth of > or = 1:380. Combined screen-positive rates were evaluated by using summation risk (NT and/or TT exhibiting a risk > or = 1:380) and calculated risk (new risk > or / =1:380, based on multiplication of LR(NT) and LR(TT)). Screen-positive rates between NT and TT differed significantly and when either test showed an increased risk for DS, the probability of the other to predict the same was negligible (p<0.001). Overall screen-positive rates, at a risk > or = 1:380, were 2% and 5.7% for NT and TT, respectively. Summation and calculated combining methods were associated with 7.5% and 2.0% screen-positive rates, respectively. Amniocentesis was performed on 20.7% of the cases, mostly screen-negative ones. Our results showed that, in normal pregnancies, NT and TT do not correlate and that their combined calculated risk in normal pregnancies is associated with a low screen-positive rate of 2.0%.

Pregnancy outcome and infant follow-up of fetuses with abnormally increased first trimester nuchal translucency.

The numbers of fetuses with an abnormal increased first trimester nuchal translucency (NT) but a confirmed normal anatomy and karyotyping is relatively small and therefore a challenge for prenatal counselling. The aim of the current study was to assess the long-term pregnancy outcome and infancy prognosis of 78 fetuses with NT > 95th centile of the normal range for crown-rump length (CRL). The most common abnormalities in this group were aneuploidy, which affected 32 of the fetuses followed by four and three cases which were miscarried or had cardiac defects respectively. The remaining euploid fetuses with normal detailed scans were followed throughout their infancy (mean 24 months; range 12-36 months). Post-natally, except for a correctable case of ventricular septal defect and a case of posterior urethral valve, no other abnormalities were detected. After excluding all aneuploid cases and using the maternal age as a second variable, an uncomplicated pregnancy outcome could be anticipated in 17 cases (100%) when the maternal age was <30 years and NT between 95th centile and 5 mm. However, the chance of a normal outcome dropped to 50% in four cases with maternal age > or =30 years and NT > or =5 mm (Fisher's exact test; P: = 0.02). These findings suggest that the long-term prognosis of the euploid fetuses with large NT (<5 mm) is reassuring in younger women.

On-to-on versus on-to-out nuchal translucency measurements.

OBJECTIVE: To analyze variables affecting the differences between on-to-on and on-to-out methods of nuchal translucency measurement. DESIGN: Prospective comparison of two methods of caliper placement. SUBJECTS: A total of 245 women undergoing transabdominal and 37 women undergoing transvaginal nuchal translucency scanning. METHODS: Nuchal translucency was measured using both on-to-on and on-to-out methods of caliper placement on the same frozen images. Differences between the methods were evaluated according to fetal size, nuchal thickness and mode of examination. Regression analysis was performed for the calculation of the expected difference between the methods at various combinations. Results among 1254 singleton pregnancies were used to set 50th, 95th and 97.5th centiles for the on-to-on method. The calculated differences were used to set 50th, 95th and 97.5th centiles for the on-to-out method. RESULTS: The mean difference between on-to-out and on-to-on nuchal translucency, using transabdominal scanning, was 0.95 +/- 0.14 mm. The differences were shown to correlate directly with fetal size and with nuchal thickness. In addition, scans performed transvaginally exhibited a smaller difference between the methods (0.90 mm vs. 0.94 mm; P < 0.05). CONCLUSION: The difference between on-to-on and on-to-out nuchal translucency measurements may have a considerable effect on the calculated risk for aneuploidy.

Conservative management of adnexal torsion in premenarchal girls.

STUDY OBJECTIVE: To evaluate treatment of premenarchal girls with torsion of the adnexa. DESIGN: Retrospective review of medical records (Canadian Task Force classification II-2). SETTING: Tertiary care, university-affiliated hospital. PATIENTS: Eight premenarchal girls (age range 3-12 yrs) with twisted adnexa. INTERVENTION: Laparoscopic detorsion and follow-up with B scan and Doppler ultrasound imaging. MEASUREMENTS AND MAIN RESULTS: Duration of complaints ranged from 8 to 72 hours (mean 34.6 hrs) and the interval from admission to surgery ranged from 6 to 24 hours (mean 18.7 hrs). Four patients had torsion of normal-appearing adnexa. The other four had ovarian neoplasms. Two had cystic mature teratomas (dermoid cysts) and one a serous cystadenoma that required additional operation. The fourth girl had a simple ovarian cyst that was aspirated laparoscopically. Seven girls (87%) had normal-appearing ovaries on follow-up ultrasound. In one patient, a small ovary was seen, with no intraovarian blood flow on color Doppler. CONCLUSION: Although the diagnosis of torsion of the adnexa in premenarchal girls is difficult and usually delayed, laparoscopic detorsion seems to be an effective adnexa-sparing approach. We suggest that laparoscopy should be the treatment of choice and that detorsion, rather than adnexectomy, be performed more often in these patients.

Comparison of nuchal translucency measurement and mid-gestation serum screening in assisted reproduction versus naturally conceived singleton pregnancies.

It has been reported that second-trimester serum markers may be affected by assisted reproduction leading to a higher false-positive rate. The current study compares 10-14 week nuchal translucency (NT) measurement and early mid-trimester serum screening in pregnancies resulting from assisted reproduction versus naturally conceived pregnancies. 75 pregnant women with a singleton pregnancy achieved by assisted reproduction underwent both 10-14 weeks NT measurement and second-trimester triple test and were followed throughout gestation. They were compared with matched controls for gestation and maternal ages. A risk of 1:380 or higher or having a fetus with Down syndrome was considered as screen-positive in both tests. The mean maternal age (30+/-3 years) and crown-rump length (61+/-9 mm) were similar, and there was no difference in NT thickness distribution between the groups. Based on NT measurement, 4 (5 per cent) women in the study and 2 (3 per cent) in the control groups, were defined as screen positive (p=NS). However, 11 (15 per cent) women in the study group and 4 (5 per cent) in the control group were found screen-positive by the triple test (p<0.05). A significantly higher amniocentesis rate of 20 per cent was noted in the study group compared with 8 per cent in the controls (p<0.05). All karyotypes were normal and no miscarriages or structural malformation were diagnosed in either group. We confirm the observation that assisted reproduction may adversely affect second-trimester screening results, which did not affect the NT screening test. Since these series are relatively small, larger series may be needed to clarify the most beneficial screening policy for this highly selected group of pregnant women.

Antenatal screening for Down's syndrome in assisted reproductive pregnancies.

The wide use of assisted conception methods has risen dramatically. The greater proportion of singletons, twins and high order of multiplicity conceived by those methods have already focused the medical community to various obstetric complications. Recently, there have been suggestions that the levels of mid-gestation serum markers, particularly human chorionic gonadotrophin (HCG), might be affected by assisted conception, leading to higher false-positive results. Furthermore, women who conceived after assisted reproduction methods are on average older, and in many cases their current pregnancy was achieved after long-standing infertility and might even be their last one. This is why they are extremely wary of any invasive fetal karyotyping. Therefore, every effort should be made to provide them with the most accurate screening of Down's syndrome (DS) risk. In this respect, nuchal translucency (NT) measurement, which has been reported to be another effective screening method, might be a more reliable marker in these pregnancies. This review explores the problematic issue of antenatal DS screening in assisted conception pregnancies. For the singletons and twins, a sequential NT and second-trimester serum marker screening can be offered, thus producing a single risk estimation which seems to be more accurate. For the high order of multiplicity, the NT offers additional important data, which can be taken in consideration both as a screening tool for DS and if fetal reduction is planned.

The feasibility of nuchal translucency measurement in higher order multiple gestations achieved by assisted reproduction.

Nuchal translucency (NT) measurement for screening chromosomal abnormalities and detecting fetal anomalies is an effective ultrasonographic marker, originally developed for singleton pregnancies. This study sought to evaluate the feasibility of NT measurements in higher order multiple gestations. Pregnant patients who conceived following assisted reproduction and were carrying three or more fetuses were enrolled in the study. Each fetus was ultrasonographically assessed, a NT measurement was obtained, and the findings were used for counselling prior to any invasive procedure. In all, 24 pregnant patients, initially carrying 79 fetuses aged 10-14 weeks of gestation, were compared with 79 consecutively matched, singleton controls, naturally conceived, having similar crown-rump lengths (+/- 3 mm). NT measurements were feasible for both study and control fetuses, which exhibited similar NT measurements for 5th, 50th and 95th centiles. Also, mean NT thicknesses [measurements in mm or multiple of the medians (MOM)] were similar for both groups (1.41 +/- 0.41 and 1.35 +/- 0.39 mm respectively and 0.87 +/- 0.23 and 0.83 +/- 0.25 MOM respectively). Prenatally no chromosomal abnormalities were detected in either group, and, of those infants who had no karyotyping, no traits were observed that warranted chromosomal analysis. NT measurements are feasible in higher order multiple gestations. Since there is no other effective screening modality for these pregnancies, it seems reasonable to recommend NT measurement for antenatal screening services for higher order multiple gestations.

Comparison of nuchal translucency measurement and second-trimester triple serum screening in twin versus singleton pregnancies.

Maternal serum screening for Down syndrome (DS) in twin pregnancies poses difficulties due to a lack of precise biochemical information about each co-twin. The current study attempts, for the first time, to compare two screening methods: nuchal translucency (NT) measurement and serum screening for DS, in twin pregnancies. 60 women with twin pregnancies (study group) underwent both first-trimester NT scanning and mid-trimester triple-marker serum screening, and were followed throughout their gestation. Nuchal translucency measurements were compared with a matched control of 120 singleton pregnancies with a similar (+/-2 years) maternal age and fetal crown-rump length (CRL) (+/-3 mm). In both analyses, a risk of 1:380, or higher, of having a DS newborn was considered screen positive. Both mean maternal age (31+/-3 years) and CRL (62+/-11 mm) were similar in the study and control groups. The median NT measurement expressed as multiples of the median (MOM) for CRL was similar in the study and control groups (0.85 and 0.88, respectively). Based on NT measurements, 5 per cent of the pregnancies in the study group and 2.5 per cent in the control group were defined as screen positive (p =N. S). Mid-gestation serum screening was associated with 15 per cent and 6 per cent screen-positive rate in study and control groups, respectively (p<0. 05). There was a ratio of 1:3 screen-positive rate between first and second-trimester screening tests within the study group. This high false-positive rate results led to 18.3 per cent amniocentesis rate in the study group compared with 7.5 per cent of the control group (p<0.03). Only one co-twin which was picked up by the NT screen was further diagnosed as trisomy 21, and one co-twin with cardiac and neural tube defect was missed by the two screening tests and was later picked up in an anomaly scan. Although the current series is too small to provoke any changes in screening practice, when twin pregnancies are diagnosed, it seems very reasonable to offer them NT measurement. A larger group may be needed to clarify which approach is the most beneficial screening policy for this highly selected group of pregnant women.