Fetal gastric size in normal and abnormal pregnancies.

OBJECTIVE: The aim of this observational study was to construct an ultrasound index of fetal gastric size for the prenatal detection of congenital digestive tract obstruction. SUBJECTS: A total of 386 fetal measurements were performed in routine ultrasonographic examinations of women with normal singleton pregnancies between 18 and 39 weeks of gestation. Gastric measurements were also performed in 13 fetuses with digestive tract obstruction. METHODS: The ultrasound plane which included the pylorus and which provided the largest stomach area was used for definition and measurement of gastric area and maximal longitudinal dimension. The transverse section at the center of the gastric corpus was used for transverse and anteroposterior dimensions. Gastric volumes were calculated as a prolate ellipsoid. The gastric area ratio was defined as the gastric area divided by the transverse abdominal area. Biparietal diameter (BPD) and abdominal transverse area were also measured. RESULTS: The fetal gastric area was significantly correlated with fetal gastric volume (r = 0.91) and gestational age (r = 0.74). However, the correlation coefficient for gastric area with gestational age was smaller than those of the BPD (r = 0.97) with gestational age and abdominal transverse area with gestational age (r = 0.97). Gastric area ratio decreased slightly towards term. The gastric area ratio was below the 95% confidence intervals for the predicted values in all five fetuses with esophageal atresia, and exceeded the 95% confidence intervals in seven of the eight fetuses with duodenal atresia or intestinal tract obstruction. CONCLUSION: Fetal gastric area correlates with ultrasound-determined gastric volume measurements and appears to be useful in the assessment of digestive tract anomalies.     

Sonographic identification and measurement of the epiphyseal ossification centers as markers of fetal gestational age

PURPOSE: This study was conducted to verify the predictive value of epiphyseal ossification center measurements in estimating gestational age. METHODS: Women with singleton pregnancies of 30-40 weeks gestation (n = 377) were enrolled in this prospective study. The distal femoral, proximal tibial, and proximal humeral ossification centers were identified and measured. A nomogram of fetal bone development was created using the sum of the three diameters. RESULTS: Gestational age correlated well with the diameters of the distal femoral and the proximal tibial epiphyseal ossification centers but even better with the sum of the three ossification centers. Positive predictive values of the fetus having gestational age of at least 37 weeks when the sum of the three centers was 7, 11, and 13 mm were 82%, 94%, and 100%, respectively. A nomogram was created using the sum of the ossification centers for 30-40 weeks' gestational age. CONCLUSIONS: Ultrasonographic visualization of the epiphyses ossification centers may be a useful marker of fetal gestational age.     

11~14周正常胎儿心脏超声检查

目的对妊娠11^＋0～14^＋6周正常胎儿心脏结构进行观察，获得该孕周内正常胎儿心脏的生理参数。方法对100位孕妇在妊娠11^＋0～14^＋6周进行常规经腹超声检查，同时观察胎儿心脏各切面结构并进行测量。结果胎儿心脏各切面显示率不同，四腔心显示率最高，其次是动脉交叉，而动脉导管的显示率最低。妊娠13周以后胎儿心脏结构超声可清晰显示。胎儿心脏周长、面积及各心室内径的增加与孕周有相关性，而心脏周长与胸廓周长比值，心脏面积与胸廓面积比值，左右心房比值以及房室率均相对衡定，与孕周之间无明显相关性。结论由于在妊娠13周以后胎儿心脏结构能够清晰显示，因此，可以将胎儿超声心动图检查时间提前至妊娠中期的早期。主要筛查与四腔心切面相关的严重的胎儿先天性心脏畸形，有利于胎儿严重先天性心脏畸形的早期诊断。     

Hemostatic changes associated with normal and abnormal pregnancies.

Routine hemostatic laboratory tests lack sensitivity and are of little value in the detection of the pregnancy associated hypercoagulable conditions. Assays for F 1 + 2, AT levels, TAT complex, APC activity, FPA, D-Dimers, tPA, plasminogen, PAI 1, and PAI 2 are more specific for fibrin formation and lysis. Monitoring these tests along with fibrinogen and platelet counts provides important information for the early detection of hemostatic activation and for monitoring the severity of the condition. Early detection and therapy is essential for limiting the deleterious complications of pregnancy. Advances in research, the development of new tests such as the TM assay and gene analysis, as well as highly skilled personnel, are required for the providing of quality pre and postnatal healthcare.     

Fetal myocardial performance in pregnancies complicated by gestational impaired glucose tolerance.

OBJECTIVE: To determine fetal myocardial performance in pregnancies complicated by mild gestational impaired glucose tolerance (GIGT). METHODS: Ultrasound examinations were performed in 37 pregnant women with mild GIGT (36 did not require insulin) and in 44 controls at 18-24, 26-30 and 34-37 weeks of gestation. The thickness of the fetal ventricular walls and interventricular septum were measured by M-mode echocardiography. Using conventional Doppler echocardiography, the mitral and tricuspid early (E) and late (A) diastolic velocities and the ventricular myocardial performance index (MPI) were determined. RESULTS: The fetuses of women with GIGT had a greater abdominal circumference (P = 0.02), a larger amniotic fluid index (P = 0.03), and a tendency to be heavier (P = 0.058) at the third scan. There were no significant differences in myocardial thickness, mitral and tricuspid E and A velocities, and E/A ratios between study and control groups. The left and right ventricular MPIs, while similar between the two groups in the first and second scans, had decreased significantly by late gestation in the GIGT fetuses (P for trend = 0.018 and 0.014, respectively) and were significantly lower than those of the control group (P = 0.002 and 0.0008, respectively). CONCLUSIONS: Fetuses of women with mild GIGT lack the ventricular hypertrophy and diastolic dysfunction that is common in fetuses of diabetic mothers, and they have a decreased MPI late in gestation. Published by John Wiley & Sons, Ltd.     

Fetal subcutaneous tissue thickness (SCTT) in healthy and gestational diabetic pregnancies.

OBJECTIVE: To determine reference values of fetal subcutaneous tissue thickness (SCTT) throughout gestation in a healthy population and to compare them with those from a population of pregnant women with gestational diabetes under standard therapy. METHODS: Three hundred and three women recruited from a high-risk pregnancy clinic were classified as being healthy (n = 218) or as having gestational diabetes (n = 85) on the basis of a negative or positive oral glucose tolerance test, respectively. They were enrolled into the cross-sectional study at 20 weeks' gestation. Ultrasound examinations were performed approximately every 3 weeks until delivery at term. The mid-arm fat mass and lean mass (MAFM, MALM), the mid-thigh fat mass and lean mass (MTFM, MTLM), the abdominal fat mass (AFM) and the subscapular fat mass (SSFM) were evaluated. Time-specific reference ranges were constructed from the 218 healthy women and a conventional Student's t-test was performed to compare SCTT values between the two study groups throughout gestation. RESULTS: Normal ranges, including 5th, 50th and 95th centiles of the distribution, were generated for each SCTT parameter obtained in each of the two groups of women. Significant differences were found between the two study groups at 37-40 weeks' gestation for MTFM, at 20-22 and 26-28 weeks for MTLM, at 31-34 and 35-37 weeks for MAFM, at 26-28 and 38-40 weeks for SSFM, and at 39-40 weeks for AFM, the mean residual values always being greater in gestational diabetic women than they were in the group of healthy pregnant women. CONCLUSIONS: We provide gestational age-specific reference values for fetal SCTT. Fetal fat mass values, particularly in late gestation, are greater in women with gestational diabetes compared with healthy women. The reference values may have a role in assessing the influence of maternal metabolic control on fetal state.     

Fetal scapular length in the ultrasonographic assessment of gestational age.

A prospective cross-sectional study of 515 singleton fetuses of ages between 15 and 42 weeks' gestation was performed. At gestational ages greater than 26 weeks, only fetuses with a sonographic estimated fetal weight between the 10th and 90th percentiles for growth were included. Scapular length (cm) as a function of gestational age (weeks) was expressed by the regression equation: SL = 0.3289 + 0.9553 (GA) with a Pearson correlation coefficient of R2 = 0.942. This study defines the normal limits of scapular length, demonstrates a high correlation between scapular length, gestational age, and other standard measurements of fetal growth, and indicates that scapular length can predict gestational age in fetuses with normal growth.     

Prostate-specific antigen in amniotic fluid of normal and abnormal pregnancies

Objective: To examine if prostate-specific antigen (PSA) is present in amniotic fluid or maternal serum during pregnancy and if its presence is associated with fetal abnormalities.

Methods: Samples tested included amniotic fluids from 853 pregnant women for whom amniocentesis was performed; 312 nonpregnant women who donated blood; 259 pregnant women who donated blood at various gestational ages. Amniotic fluid or serum PSA was measured with an ultrasensitive time-resolved immunofluorometric procedure. 372 pregnancies were studied for the presence of genotypic or phenotypic fetal abnormalities.

Results: PSA was present in most amniotic fluids; the median PSA concentration increased from gestational week 11 to 22 and stabilized thereafter until delivery. The most prominent PSA concentration change occurred during gestational weeks 13–14. Pregnant women had significantly higher serum PSA concentrations than nonpregnant women; the pattern of serum fSA concentration change during pregnancy was similar to that of amniotic fluid; however, serum PSA concentrations were lower by a factor of 20–40. No association existed between amniotic fluid F'SA and maternal age, gender of fetus, or length of abstinence of mother from sexual intercourse. After gestational week 15, fetuses with trisomy 21 or 18, anencephaly, or renal disorders were associated with low amniotic fluid PSA levels.

Conclusion: Our data suggest that PSA may play a role in fetal development, especially at gestational ages between 13–20 weeks. The diagnostic usefulness of PSA in identifying fetal abnormalities remains to be determined.     

Independent component analysis of normal and abnormal rhythm in twin pregnancies

We investigated the utility of ICA for evaluation of fetal rhythm in five uncomplicated twin pregnancies and in five twin pregnancies complicated by fetal arrhythmia. Using objective and subjective criteria, we sought to determine how the signal-to-noise ratio, signal fidelity and interference rejection are affected when synthesizing the fetal signal using all the signal-containing ICA components (rank-p ICA) versus using the single dominant component (rank-1 ICA). The signal of each fetus was most commonly distributed over 1 or 2 ICA components, as previously observed in studies of singleton pregnancies; however, in 8 of 26 (31%) cases the signal of each fetus was distributed over 3, 4 or even 5 ICA components. Rank-1 ICA provided the highest SNR and interference rejection, but at the cost of reduced signal fidelity. Our results corroborate that in twin pregnancies, including twin pregnancies complicated by fetal arrhythmia, rank-1 ICA is very effective in isolating the QRS complexes of each fetus; however, it has some limitations when used for fetal rhythm evaluation due to signal distortion. Occasionally, rank-1 ICA completely separates the P-wave and the T-wave from the QRS complex, thus requiring the mixing of several ICA components to achieve acceptable signal fidelity.     

Fetal middle cerebral to uterine artery pulsatility index ratios in normal and pre-eclamptic pregnancies.

OBJECTIVES: To calculate the normal range for the fetal middle cerebral artery (MCA)/uterine artery pulsatility index (PI) ratio in the third trimester of pregnancy and to assess its value, compared with that of the MCA/umbilical artery PI ratio, in predicting an unfavorable outcome of pregnancies complicated by pre-eclampsia. METHODS: Doppler blood flow velocimetry of the uterine and umbilical arteries and fetal MCA was performed. We calculated the ratios between 1) the PI of the MCA and the mean PI value of both uterine arteries and 2) the PI of the MCA and the PI of the umbilical artery. All women were examined at or beyond 26 weeks of gestation. A cross-sectional study of 231 normal pregnancies was conducted to construct the reference range. Values below the 5th percentile or an MCA/umbilical artery PI ratio lower than 1.08 were defined as brain-sparing. A further 115 pregnancies with pre-eclampsia (50 mild and 65 severe) were assessed prospectively and the results were related to perinatal outcome. The accuracy of MCA/uterine artery and MCA/umbilical artery PI ratios for prediction of unfavorable pregnancy outcome was compared. RESULTS: Normal MCA/uterine artery PI ratios decreased with advancing gestational age. Redistribution of the fetal circulation indicated by a low MCA/uterine artery PI ratio was seen in 30% of the mild (n=15) and 46% of the severe (n=30) pre-eclamptic cases. There was a significant difference between those without and those with signs of brain-sparing, respectively, in mean birth weight (2456.0 vs. 1424.5 g), gestational age at delivery (35.6 vs. 31.3 weeks) and gestational age at the time of examination (34.9 vs. 30.9 weeks). Furthermore, there was a significantly higher rate of small-for-gestational-age (SGA) neonates (57.8% vs. 25.7%), preterm delivery (100% vs. 81.8%) and Cesarean section (90.7% vs. 66.7%) in cases with an MCA/uterine artery PI ratio below the 5th percentile. However, there was no difference between the groups in the rate of low 5-min Apgar scores, admission to the neonatal intensive care unit, or deliveries before 34 weeks. The MCA/uterine artery and MCA/umbilical artery PI ratios were similar in the prediction of adverse perinatal outcome. Both ratios were better at predicting the outcome of pregnancy than were signs of increased vascular impedance in either the umbilical or uterine arteries. CONCLUSIONS: Normal MCA/uterine artery PI ratio decreases with gestational age. Abnormally low MCA/ uterine artery PI ratios are related to unfavorable pregnancy outcome. The predictive value of the MCA/uterine artery PI ratio is similar to that of the MCA/umbilical artery PI ratio.     

Fetal blood sampling in twin pregnancies.

OBJECTIVE: To evaluate the role of fetal blood sampling for prenatal diagnosis in twin pregnancies. METHODS: This was a retrospective study of 84 twin pregnancies that had undergone fetal blood sampling between the years 1977 and 2000. These results were compared with those from a similar study on amniocentesis and chorionic villus sampling. RESULTS: Miscarriage occurred in 3.6% of cases after fetal blood sampling. The total fetal loss rate was 13.6% and the fetal loss that could be attributed to the procedure was 8.2%. The procedure-related fetal loss rate was dependent on the indication for fetal blood sampling. The rates of preterm delivery at 28 weeks and neonatal mortality were 16.9%, 28.3%, 10.9%, 3.1% and 7.7%, respectively. CONCLUSION: Fetal blood sampling in twin pregnancies carries higher risks for the fetus than do amniocentesis and chorionic villus sampling. However, it remains useful in evaluating the fetal condition in special circumstances such as hydrops and infection.     

Distinguishing normal from abnormal gestational sac growth in early pregnancy

In order to evaluate normal and abnormal gestational sac development, serial sonograms were performed in 83 women whose initial sonogram demonstrated a gestational sac lacking a detectable embryo. Of 53 normal gestations, the mean sac growth was 1.13 mm/day (range, 0.71-1.75). In comparison, of 30 abnormal gestations, 24 demonstrated sac growth, and of these, the mean growth was 0.70 mm/day (range, 0.14-1.71). Based on these observations, we suggest that gestational sac growth of less than or equal to 0.6 mm/day is evidence for abnormal development. Analysis of the initial and follow-up scans for the 53 normal gestations showed that a living embryo was always detected when the mean gestational sac was greater than 25 mm in average diameter, and a yolk sac was always seen when the mean sac diameter was greater than 20 mm. In comparison, of 30 abnormal gestations, six were greater than 25 mm without a detectable embryo, and four were greater than 20 mm without a yolk sac. Recommendations for the optimal time of a follow-up sonogram are presented based on the initial sac size.     

Fetal aneuploidy and umbilical cord thickness measured between 14 and 23 weeks' gestational age.

OBJECTIVE: To evaluate and compare umbilical cord thickness of aneuploid fetuses with umbilical cord diameter nomograms generated from euploid fetuses between 14 and 23 weeks' gestational age. METHODS: A retrospective study was conducted in which 56 fetuses and neonates had diagnoses of abnormal karyotypes, of which 46 fetuses had numerical chromosomal abnormalities. Among these cases, 26 subjects with adequate umbilical cord sonographic images were included in the study. The umbilical cord thickness was measured and plotted against the umbilical cord diameter nomogram that was generated from previously published data. RESULTS: From 26 evaluated fetuses and neonates, in 14 subjects (53.8%), the umbilical cord thickness was greater than the 95th percentile for gestational age. A thick umbilical cord was observed in 57.8% of fetuses with trisomy 21 and 50% of subjects with trisomy 18 and monosomy 45,XO. One fetus with trisomy 2 had umbilical cord thickness within the normal range. The largest number of aneuploid fetuses with thick umbilical cords (87.5%) was observed between 16 and 17 gestational weeks. CONCLUSION: Aneuploid fetuses have thicker umbilical cords than euploid fetuses. The umbilical cord thickness can be related to an increased amount of Wharton jelly. Because of the smaller number of thick umbilical cords in aneuploid subjects at later gestational ages, we speculate that abnormal cord thickness has a natural tendency toward its own resolution with the advancement of gestational age.     

Fetal peripheral bronchial fluid flow during breathing movement in normal pregnancies: a preliminary study.

OBJECTIVE: To determine the fluid flow velocity waveforms in the fetal peripheral bronchus during fetal breathing movement by means of pulsed Doppler ultrasonography. DESIGN: A preliminary cross-sectional study. SUBJECTS: Twenty-eight normal pregnant women between 32 and 38 weeks of gestation. METHODS: Velocity waveforms from fetal peripheral respiratory fluid flow were acquired from the segmental bronchus (B6 or B8) which runs along the segmental artery (A6 or A8). The maximum velocity of the intrabronchial fluid flow and duration of inspiratory and expiratory phases were quantified. RESULTS: The flow velocity signal from the fluid in the fetal segmental bronchus of 17 of the 28 fetuses was detected. We observed two types of fetal breathing movement. CONCLUSION: During fetal breathing movement, the fluid in the fetal respiratory tract moves in the fetal segmental bronchus. This movement can be detected by pulsed Doppler velocimetry aided by power Doppler ultrasonography.     

Fetal transcerebellar diameter measurement for prediction of gestational age at the extremes of fetal growth.

OBJECTIVE: The purpose of this study was to determine the accuracy of our previously published and prospectively validated transcerebellar diameter (TCD) nomogram in the prediction of gestational age (GA) in intrauterine growth-restricted (IUGR) and large fetuses. METHODS: We established a cross-sectional nomogram of TCD in 24,026 well-dated singleton fetuses and prospectively validated the nomogram using 2597 fetuses from a separate population. This nomogram was validated in both IUGR (n = 55) and large (n = 16) fetuses (estimated fetal weight, <10th and >90th percentiles, respectively). The actual GA was subtracted from the TCD-predicted GA in IUGR and large fetuses, and the concordance between the actual and predicted GAs was assessed using the Pearson correlation coefficient. RESULTS: Concordance between the actual and predicted GA based on our previously published singleton TCD nomogram was high for both IUGR and large fetuses (Pearson correlation, r = 0.98 and 0.95, respectively; P < .001). The means (SDs) of actual and predicted GA based on TCD in IUGR fetuses were 24.9 (6.5) and 25.1 (6.3) weeks, respectively. The predicted GA based on TCD in IUGR fetuses was within 3 days in 97.5% in the second trimester and 93.3% in the third trimester. In large fetuses, the difference between the actual and predicted GA based on TCD within 3 days was 100% in both the second and third trimesters. CONCLUSIONS: This study shows that our institution-specific TCD nomogram is reliable and accurate in predicting GA even at extremes of fetal growth.     

Fetal overnutrition in polynesian pregnancies and in gestational diabetes may lead to dysregulation of the adipoinsular axis in offspring

OBJECTIVE: To compare umbilical cord leptin concentrations in different ethnic groups and between pregnancies with and without gestational diabetes mellitus (GDM) in Auckland, New Zealand. RESEARCH DESIGN AND METHODS: A cross-sectional study of 116 European, Polynesian, and South Asian women and their infants with and without GDM. Maternal metabolic measures were recorded at 36 weeks' gestation, umbilical cord samples were collected at birth, and neonatal anthropometric measures were recorded 24 h after delivery. RESULTS: Compared with Europeans and South Asians, samples of Polynesian umbilical cords had higher leptin concentrations (8.7 and 9.5 vs. 14.9 ng/ml, respectively; P = 0.026). Umbilical cord samples from pregnancies complicated by GDM had higher leptin concentrations than those from normal pregnancies (22.3 vs. 13.8 ng/ml, respectively; P = 0.022). Maternal leptin concentrations at 36 weeks were similar across ethnic groups and with and without GDM. Cord leptin correlated with birth weight, measures of fetal size, and cord insulin in normal pregnancies and those complicated by GDM. In multivariate analyses, cord leptin was related to birth weight (P < 0.001), gestation at delivery (P = 0.038), and ethnic group (P = 0.017) in normal pregnancies and to birth weight (P < 0.001), gestation at delivery (P < 0.001), and sex (P = 0.003) but not maternal diabetes status (P = 0.909) in pregnancies complicated by GDM. CONCLUSIONS: Offspring of Polynesian women are relatively hyperleptinemic, independent of birth size. Offspring of women with GDM are also relatively hyperleptinemic at birth, but this was associated with their increased birth weight. We speculate that this GDM-associated relative hyperleptinemia may be due to fuel-mediated teratogenesis affecting the adipoinsular axis, which in turn could also lead to leptin resistance and obesity in adult life. The reason for the ethnic difference in hyperleptinemia is unclear.     

Fetal heart rate in chromosomally abnormal fetuses.

OBJECTIVES: To determine the effects of chromosomal defects on fetal heart rate at 10-14 weeks of gestation. METHODS: Fetal heart rate at 10-14 weeks of gestation in 1061 chromosomally abnormal fetuses was compared to that from 25,000 normal pregnancies. The chromosomally abnormal group included 554 cases of trisomy 21, 219 cases of trisomy 18, 95 of trisomy 13, 50 of triploidy, 115 of Turner syndrome and 28 of sex chromosome abnormalities other than Turner syndrome. RESULTS: In the normal group, fetal heart rate decreased from a mean value of 170 beats per minute (bpm) at 35 mm of crown-rump length to 155 bpm at 84 mm crown-rump length. In trisomy 21, trisomy 13 and Turner syndrome fetal heart rate was significantly higher, in trisomy 18 and triploidy the heart rate was lower and in other sex chromosome defects it was not significantly different from normal. Fetal heart rate was above the 95th centile of the normal range in 10%, 67% and 52% of fetuses with trisomy 21, trisomy 13 and Turner syndrome, respectively. The fetal heart rate was below the 5th centile in 30% of fetuses with triploidy and 19% of those with trisomy 18. CONCLUSIONS: Trisomy 21, trisomy 13 and Turner syndrome are associated with fetal tachycardia, whereas in trisomy 18 and triploidy there is fetal bradycardia. Inclusion of fetal heart rate in a first-trimester screening program for trisomy 21 by a combination of maternal age and fetal nuchal translucency thickness is unlikely to provide useful improvement in sensitivity.     

Relationship between normal oral glucose tolerance test in women at risk for gestational diabetes and large for gestational age infants.

OBJECTIVE: To determine whether the glycemic status of pregnant women with a normal 3-h 100-g oral glucose tolerance test (OGTT) is related to outcome with respect to large for gestational age (LGA) infants. RESEARCH DESIGN AND METHODS: A prospective study of 2631 women was conducted. One hundred seventy-six women had an OGTT based either on a 1-h 50-g OGTT (n = 105) or clinical risk factors (n = 71). Thirty-three women were diagnosed as having gestational diabetes mellitus. RESULTS: Negligible discriminatory capacity for the variables with respect to prediction of LGA infants was indicated by the areas under the receiver operating characteristic (ROC) curves for fasting blood glucose, 2-h OGTT blood glucose, and the OGTT response curve area for women with a normal OGTT (n = 143). However, a statistically significant increased incidence of LGA infants was established for both the OGTT-positive and normal OGTT groups (P less than 0.0001). Multiparity, a maternal weight greater than or equal to 70 kg, and birth of a male infant were other factors associated with a significantly increased frequency of LGA infants. CONCLUSIONS: The results may be interpreted as either indicating a role for confounding variables, i.e., maternal weight, multiparity, and birth of a male infant, or the imprecision of the OGTT in assessing physiologically important changes in maternal hyperglycemia.     

Assessment of weight and gestational age.

Many established nursery routines are in conflict with the physician's responsibility to the infant and the needs of the mother. While the first hour after birth is a crucial time for the mother and the infant to be together, it is also a time when neonatal problems can be identified and often prevented. Unless a problem is suspected immediately, this first hour of life is not the time for a thorough examination. The assessment of gestational age may be carried out later, in the nursery, when the infant's condition has stabilized and the parents have had an opportunity to view their infant.     

Fetal nuchal translucency screening in 12495 pregnancies in Sardinia.

OBJECTIVE: To examine the distribution of fetal nuchal translucency thickness in normal and chromosomally abnormal fetuses in Sardinia and to determine the effectiveness of screening by a combination of fetal nuchal translucency and maternal age. METHODS: Fetal nuchal translucency thickness and crown-rump length were measured at 10-14 weeks of gestation in 12 495 pregnancies. A reference range of fetal nuchal translucency thickness for crown-rump length was determined from the 10 001 singleton pregnancies with known normal pregnancy outcome. The median nuchal translucency thickness for crown-rump length was determined by regression analysis of the calculated median values of nuchal translucency thickness for each 0.1 mm interval in crown-rump length. The proportions of unaffected fetuses and those with trisomy 21 or other chromosomal defects with nuchal translucency thickness > 1.5 and 2.0 multiples of the regressed normal median for crown-rump length were calculated. The distribution of estimated risks based on maternal age and fetal nuchal translucency thickness according to The Fetal Medicine Foundation software were also determined and the sensitivity and false-positive rates were calculated. RESULTS: In the 10 001 normal pregnancies, the median fetal nuchal translucency thickness increased with crown-rump length (median nuchal translucency thickness = 0.3496 + 0.018 x crown-rump length) (r2 = 0.4411). In the singleton pregnancies, there were 64 fetuses with trisomy 21 and 46 with other chromosomal defects. The fetal nuchal translucency thickness was > 1.5 multiples of the median in 510 (5%) of the normal fetuses, in 52 (81%) of the trisomy 21 fetuses and in 33 (72%) of those with other chromosomal defects. The respective values for nuchal translucency thickness > 2.0 multiples of the median were 195 (2%), 41 (64%) and 32 (70%). In 184 multiple pregnancies, there were four fetuses with chromosomal abnormalities and in three of these the nuchal translucency thickness was > 1.5 multiples of the median. Screening by a combination of maternal age and fetal nuchal translucency thickness with a risk cut-off of 1 in 300 identified 90% of trisomy 21 pregnancies and 85% of all other chromosomal defects for a false-positive rate of 9%. CONCLUSION: Screening for chromosomal defects by measurement of nuchal translucency thickness identifies 80% of fetuses with trisomy 21 for a false-positive rate of 5%. In our population with a median maternal age of 33 years, screening by a combination of maternal age and fetal nuchal translucency thickness with a risk cut-off of 1 in 300 identified 90% of trisomy 21 pregnancies for a false-positive rate of 9%.