First trimester umbilical artery pulsatility index in fetuses presenting enlarged nuchal translucency

The aim of this prospective study was to evaluate an umbilical artery pulsatility index (UAPI) in first trimester fetuses who present enlarged nuchal translucency (NT) measurements. UAPI was measured in 121 single fetuses with NT > or =95th centile, from 10+3 to 13+6 weeks (crown-rump length (CRL) > or =38 mm - < or =84 mm). In these fetuses there were 20 trisomy 21, and six other chromosomal abnormalities (three trisomy 18 and three monosomy X). Eighty-nine cases had normal karyotype and delivered a baby without evidence of congenital malformations. Five fetuses with normal karyotype assessed antenatally were excluded from the comparison, because of evidence of congenital malformation. A fetus with normal karyotype that was spontaneously miscarried at 14 weeks' after chorionic villus sampling was also excluded. UAPI of fetuses with enlarged NT was compared with those of 65 singleton fetuses with normal NT and normal karyotype, which were used to establish our terms of reference (5th centile, median and 95th centile). UAPI of 7/20 (35%) Down syndrome and 42/89 (47%) normal karyotype fetuses presenting enlarged NT were above the median, and respectively 2/20 (10%) and 14/89 (15.7%) were above 95th centile of normal NT and normal karyotype fetuses. No significant differences were demonstrated in the UAPI values amongst normal karyotype fetuses with normal NT or normal karyotype fetuses with an enlarged NT or trisomy 21 fetuses with an enlarged NT.     

Increased nuchal translucency with normal karyotype

Increased fetal NT thickness is a common phenotypic expression of trisomy 21 and other chromosomal abnormalities, but it is also associated with fetal death and a wide range of fetal malformations, deformations, dysgenesis, and genetic syndromes. This paper reviews the outcome of chromosomally normal fetuses with increased NT On the basis of these data it is possible to estimate, for each NT group, the chances of intrauterine survival and delivery of a healthy baby with no major abnormalities. These data are useful in counselling parents of pregnancies with increased fetal NT and in planning the appropriate follow-up investigations. In normal fetuses NT thickness increases with fetal crown-rump length (CRL). The median and 95th centile of NT at a CRL of 45 mm are 1.2, and 2.1mm and the respective values at CRL of 84mm are 1.9 and 2.7 mm. The 99th centile does not change significantly with CRL and it is about 3.5 mm. Increased NT, refers to a measurement above the 95th centile and the term is used irrespective of whether the collection of fluid is septated or not and whether it is confined to the neck or envelopes the whole fetus. After 14 weeks, increased NT usually resolves but in some cases it evolves into nuchal edema or cystic hygromas.     

Estimation of ultrasonographic markers of chromosomal abnormalities in verification of second trimester maternal serum biochemistry

In the case of positive triple test results the presence or absence of sonographic markers is associated not only with fetal abnormalities, but also with a variety of adverse outcomes of pregnancy. OBJECTIVE: Evaluation of sonographic markers of chromosomal abnormalities in verification of positive results of triple tests. MATERIAL AND METHODS: In consecutive series of 780 pregnant women we performed triple tests at 14-19 weeks. We reviewed the presence or absence of sonographic markers for fetal abnormalities including nuchal thickening (NT), nasal bones (NB), extermities (HL, FL), umbilical cord diameter (UCD), bowel echogenity (BE), renal pyelectasis (DPR) and chorioid plexus cyst (CPC). RESULTS: There were 47 (6.02%) positive results of triple tests including 36 (4.6%) cases with false positive result. In the group of affected fetuses we observed at least two sonographic markers. In the group with false-positive results 15 (41.6%) fetuses had adverse pregnancy outcome with only one ultrasound marker. CONCLUSION: Positive result of the triple test and the presence of two or more markers of fetal abnormalities increase the risk of fetal abnormalities, whereas absence or presence of only one marker and normal karyotype should classify pregnancy to high risk of adverse perinatal outcome.     

The value of sonography in early pregnancy for the detection of fetal abnormalities in an unselected population.

OBJECTIVE: To determine the value of early pregnancy sonography in detecting fetal abnormalities in an unselected obstetric population. DESIGN Prospective cross-sectional study. All women initially underwent transabdominal sonography and when the anatomical survey was considered to be incomplete, transvaginal sonography was also performed (20.1%). Nuchal translucency was measured and karyotyping was performed as appropriate. SETTING: University Department of Obstetrics and Gynaecology. PARTICIPANTS: 6634 sequential unselected women (mean maternal age 29.9 years, range 13-50; mean gestational age 12+4 weeks, range 11+0-14+6), carrying 6443 live fetuses participated in this study. MAIN OUTCOME MEASURE: Detection rate of fetal anomalies and the associated cost per case detected in early pregnancy. RESULTS: The incidence of anomalous fetuses was 1.4% (92/6443) including 43 chromosomal abnormalities. The detection rate for structural abnormalities was 59.0% (37/63, 95% CI 46.5-72.4) and the specificity was 99.9% in early pregnancy. When the first and second trimester scans were combined, the detection for structural abnormalities was 81.0% (51/63, 95% CI 67.7-89.2). Seventy-eight percent (31/40) of chromosomal abnormalities (excluding three cases of XXY) were diagnosed at 11-14 weeks, either because of a nuchal translucency greater than or equal to the 99th centile for gestational age (43%; 17/40, 95% CI 27.4-60.4), or due to the presence of structural abnormalities (35%; 14/40, 95% CI 21.2-52.8). Sixty-five percent (15/23) of cases of trisomy 21 were also diagnosed either because of having a nuchal translucency greater than or equal to the 99th centile (57.0%; 13/23) or due to the presence of a structural abnormality (9.0%; 2/23). Overall, the detection rate of structurally abnormal fetuses was 59% (37/63) in early pregnancy and 81% in combination with the second trimester scan. The cost per abnormality diagnosed in early pregnancy is estimated to be pound sterling 6258 per structurally abnormal fetus, pound sterling 7470 per chromosomal abnormality and pound sterling 4453 per anomalous fetus. CONCLUSION: The majority of fetal structural and chromosomal abnormalities can be detected by sonographic screening at 11-14 weeks, but the second trimester scan should not be abandoned.     

Chromosomal abnormalities in fetuses with ultrasonographically detected neural tube defects

We analyzed the karyotype of fetuses with ultrasonographically detected neural tube defects (NTDs). In our study, we included a total of 194 fetuses with NTDs. We analyzed the type of NTD, the karyotype, maternal age, fetal gestational age at diagnosis, and fetal sex. Of the 194 fetuses with NTDs, 87 were anencephalic and 107 had other, nonanencephalic, NTDs. A total of 12 fetuses were shown to have chromosomal abnormalities. Three of 87 anencephalic fetuses (3.45%) had chromosomal abnormalities. The sex ratio for anencephalic fetuses was 65.5% : 34.5% for female and male fetuses. Nine of 107 fetuses with other NTDs (8.41%) had chromosomal abnormalities. Seven fetuses had isolated NTDs and a further seven fetuses had additional ultrasonographic anomalies. Two of the latter had abnormal karyotypes. The sex ratio of all other NTD cases was 67.3% : 32.7% for female and male fetuses. The high number of chromosomal abnormalities justifies prenatal karyotyping in all fetuses with ultrasonographically diagnosed NTDs.     

Rapid karyotyping in fetuses with abnormal sonogram

Prenatal karyotyping of fetuses having an abnormal sonogram was undertaken in 27 pregnancies between 17 and 39 weeks, using fetal blood obtained by percutaneous umbilical cord blood sampling under ultrasound guidance. Eight chromosomal abnormalities (29.7%) were detected, including 45, X (2 cases), trisomy 21(1 case), 46, XY,-13,+t(13,13) (1 case), 47, XX,+18(3 cases), 47, XXY (1 case). Nineteen fetuses had a normal karyotype (46,XX:9 cases, 46,XY:10 cases). The fetal karyotype was available within 72 h and fetal management was planned accordingly. We concluded that in fetuses with an abnormal sonogram, rapid karyotyping using fetal blood obtained under ultrasound guidance had important implications in obstetric and neonatal management and would facilitate genetic counselling.     

Increased nuchal translucency and congenital heart defects in a low-risk population

OBJECTIVE: Increased first-trimester nuchal translucency (NT) is a possible marker for congenital heart defects in euploid fetuses. In this study, we wanted to determine the sensitivity for congenital heart defects using the 95th centile of the NT as a cut-off point. METHODS: All women who booked for delivery in our hospital in the first trimester underwent NT measurement at a crown-rump length (CRL) of between 35 and 75 mm. In all euploid fetuses and newborns with isolated or associated CHD, NT was examined retrospectively and classified as normal (<95th centile according to CRL-dependent centiles in our own data) or increased (> or =95th centile). RESULTS: From a total of 12,978 euploid fetuses screened, 27 had CHD (22 isolated and 5 cases associated with additional malformations). Moreover, 7 of the 27 fetuses also had increased NT (26%). Increased NT was significantly more frequent in fetuses with associated CHD (4/5) than in those with isolated CHD (3/22, Yates corrected chi2 p=0.012). In fact, the relative risk for CHD was 6.6 times higher in fetuses with increased NT compared to those with normal NT. CONCLUSION: Increased NT for the detection of CHD performed less well than in other studies. Nevertheless, it can be used as an indication for fetal echocardiography.     

First trimester sonographic detection of chromosomal abnormalities in an unselected population

Objective To investigate the role of first trimester sonography in detecting chromosomal abnormalities in an unselected obstetric population.
Methods 2281 women (mean maternal age 30 years [range 16-47]; mean gestational age 12⁺³ weeks [range 11-14]) underwent transabdominal scanning to assess fetal structure and, if anatomical survey was considered to be incomplete (31% of cases), transvaginal sonography was also performed. Measurement of nuchal translucency was included and karyotyping performed as considered appropriate.
Results There were 16 chromosomal abnormalities; 13 (81%) were diagnosed at 11-14 weeks either because of a nuchal translucency greater than or equal to the 99th centile for gestational age (7/16; 44% [95% CI 25-63]) or due to the presence of structural abnormalities (6/16; 38% [95%CI 14.2–61.81). Seventy-five percent of cases of trisomy 21 were also diagnosed either because of having a nuchal translucency greater than or equal to the 99th centile (5/8; 63%) or due to the presence of a structural abnormality (1/8; 13%).
Conclusions A significant proportion of fetal chromosomal abnormalities can be detected by first trimester sonographic screening to assess fetal structural appearance. The sensitivity of detection can be improved by combining measurement of nuchal translucency with detailed examination of fetal anatomy.     

Relation between increased fetal nuchal translucency thickness and chromosomal defects

OBJECTIVE: To examine the prevalence and distribution of all chromosomal defects in fetuses with increased nuchal translucency thickness. METHODS: Assessment of risk for trisomy 21 was carried out by a combination of maternal age and fetal nuchal translucency thickness at 11-13 + 6 weeks. A search of the database was made to identify, first, all singleton pregnancies in which fetal karyotyping was carried out and, second, the cases where the fetal nuchal translucency was equal to or above the 95th centile for fetal crown-rump length. The prevalence and distribution of chromosomal defects were determined for each nuchal translucency category: between the 95th centile for crown-rump length and 3.4 mm, 3.5-4.4 mm, 4.5-5.4 mm, 5.5-6.4 mm, 6.5-7.4 mm, 7.5-8.4 mm, 8.5-9.4 mm, 9.5-10.4 mm, 10.5-11.4 mm, and 11.5 mm or more. RESULTS: The search identified 11,315 pregnancies. The median maternal age was 34.5 (range 15-50) years, and the median fetal crown-rump length was 64 (range 45-84) mm. The fetal karyotype was abnormal in 2,168 (19.2%) pregnancies, and the incidence of chromosomal defects increased with nuchal translucency thickness from approximately 7% for those with nuchal translucency between the 95th centile for crown-rump length and 3.4 mm to 75% for nuchal translucency of 8.5 mm or more. In the majority of fetuses with trisomy 21, the nuchal translucency thickness was less then 4.5 mm, whereas in the majority of fetuses with trisomies 13 or 18 it was 4.5-8.4 mm, and in those with Turner syndrome it was 8.5 mm or more. CONCLUSION: In fetuses with increased nuchal translucency, approximately one half of the chromosomally abnormal group is affected by defects other than trisomy 21. The distribution of nuchal translucency is different for each type of chromosomal defect. LEVEL OF EVIDENCE: II-3.     

First-trimester ductus venosus velocimetry in relation to nuchal translucency thickness and fetal karyotype.

AIM: To evaluate first-trimester ductus venosus flow in relation to nuchal translucency (NT) and fetal karyotype. METHODS: Ductus venosus flow was measured in fetuses with NT greater than or equal to the 95th centile (group A) and in fetuses with NT less than the 95th centile (group B). The waveforms were classified as normal if the lowest forward velocity during atrial contraction (ACV) was positive and abnormal if it was absent or negative. The results were compared with the fetal karyotype. RESULTS: Ductus venosus measurement was carried out in 330 fetuses. In group A, there were 156 fetuses: in 4 cases, it was not possible to obtain the measurement, and in the other 152 cases, 93 (61%) had a normal ACV and 59 (39%) an abnormal ACV. NT thickness was significantly greater in fetuses with abnormal ACV. In 34 out of 156 cases (22%), chromosomal abnormalities were found. Twenty-three chromosomopathies out of 33 (70%) had an abnormal ACV, and 10 (30%) had a normal ACV. A significant association between abnormal karyotype and abnormal ACV was found. Ductus venosus measurement was carried out in 174 fetuses of group B. In 1 case, it was not possible to obtain the measurement. One hundred and seventy-one (99%) cases had a normal ACV, and in 2 (1%) cases the ACV was abnormal. No chromosomal abnormalities were found in group B. Considering group A and group B, a significant association between the finding of an enlarged NT and abnormal ACV was detected (p < 0.05). CONCLUSIONS: An abnormal ACV is more frequent in fetuses presenting enlarged NT than in those having normal NTs and in fetuses having the larger nuchal thickness. The probability of having a chromosomal abnormality in fetuses with enlarged NT is greater when an abnormal ACV is found.     

Nuchal translucency as a predictor of adverse pregnancy outcome.

BACKGROUND: Thickened nuchal translucency (NT) has been related to fetal genetic syndromes, structural abnormalities, and other diseases. The aim of this research was to evaluate the association of NT with adverse pregnancy outcomes. STUDY DESIGN: In the period 2002-2004 in 2104 pregnant women between 10+6 and 13+5 weeks' gestation, NT was evaluated as a parameter for aneuploidy screening: out of these, 734 singleton pregnant women that underwent 2nd trimester amniocentesis and whose pregnancy outcome were known were selected. NT was statistically correlated to pregnancy and neonatal outcome. RESULTS: Median gestational age (GA) at NT evaluation was 11+2 weeks' gestation. NT median was 1.1 mm (0.9-1.4 mm, 25th-75th centile, range 0.5-4.0 mm). After multiple logistic regressions, the variables significantly associated to NT values were: threatened preterm labor (p<0.008) and preterm labor (p<0.02). The best diagnostic accuracy point was NT>95th centile and >1.5 MoM for the prediction of threatened preterm labor. CONCLUSION: In this series, increased NT values were associated to threatened preterm labor and preterm labor in euploid fetuses: this finding may have clinical consequences in the management of such pregnancies.     

Spine length measurement in the first trimester of pregnancy

OBJECTIVES: The aim of the study was to evaluate spine length as an indicator of skeletal growth in the first trimester of pregnancy and to provide a nomogram of spine length at the end of the first trimester of pregnancy. METHODS: The study was carried out on 420 single pregnancies, at gestational ages ranging from 11 to 14 weeks, using high-resolution transabdominal echography. Biparietal diameter and crown-rump length (CRL) were measured to date the pregnancy. Using the same scanning plane used to measure CRL, the whole spine length in antero-dorsal position can be visualized as a double hyperechoic line from 10 weeks of gestation onwards. Spine length was measured three times by one observer and the mean of the three measurements was considered as definitive. Forty fetuses had multiple measurements for interobserver and intraobserver error analysis. RESULTS: Linear relationship between spine length, and gestational age, biparietal diameter and CRL were demonstrated. Spine length (millimetres) as a function of gestational age (days) was expressed by the regression equation: spine length = 1.09 x (gestational age in days) -60.56, with a determination coefficient of R(2) = 0.744. Spine length ranged from 21.5 mm at 11 weeks to 41.9 mm at 14 weeks. CONCLUSION: The data obtained showed that spine length increased progressively from the end of the first trimester to the beginning of the second. A high correlation between spine length, gestational age, biparietal diameter, and CRL was observed. Spine length measurement could therefore be considered a good indicator of fetal growth.     

First trimester fetal ultrasound parameters associated with PAPP-A and fβ-hCG

Objective: To study the association of fβ-hCG and PAPP-A measured at 11–14 weeks of gestation with delta crown-rump-length (dCRL), delta fetal heart rate (dFHR) and delta nuchal translucency (dNT). To calculate adjusted MoM taking into consideration these associations. Methods: Retrospective cross-sectional study on 5,536 singleton euploid pregnancies participating in a first trimester screening program for chromosomal abnormalities by nuchal translucency and maternal serum biochemistry. Adjusted MoM were calculated for fβ-hCG and PAPP-A and compared to the observed MoM (calculated by the Fetal Medicine Foundation screening algorithm). Results: fβ-hCG correlates positively with dCRL and negatively with dNT, whereas PAPP-A shows a positive correlation with dNT and a negative one with dCRL and dFHR. After adjustment for the ultrasound parameters, the median MoM values for fβ-hCG and PAPP-A changed from 1.02 and 0.92 observed MoM to 0.98 and 0.99 adjusted MoM respectively. The difference between the observed and adjusted MoM was statistically significant (p?<?0.001). Delta CRL increases with gestation and this effect manifests mainly after CRL of 62?mm. Conclusions: Adjustment for dCRL, dFHR and dNT improves the calculation of MoM for fβ-hCG and PAPP-A. CRL measurement overestimates fetal size at the end of the screening period 11–14 weeks.     

Screening for fetal aneuploidies and fetal cardiac abnormalities by nuchal translucency thickness measurement at 10-14 weeks of gestation as part of routine antenatal care in an unselected population.

OBJECTIVES: To evaluate first trimester pregnancy screening for fetal aneuploidy and congenital heart defects by maternal age and nuchal translucency measurement and screening for fetal aneuploidies and congenital heart defects by ultrasound in an unselected population. DESIGN: A prospective study. SETTING: Fetal medicine unit, St George's Hospital, London. SAMPLE: 4523 consecutive viable fetuses at 10-14 weeks with a crown-rump length between 38 and 80 mm were scanned transabdominally (93%) or transvaginally (7%). METHODS: Screening was performed by calculating the background risk from maternal age, gestational age and obstetric history, which was then adjusted with the nuchal translucency measurement in relation to crown-rump length (adjusted risk). MAIN OUTCOME MEASURES: Measurements of crown-rump length and nuchal translucency thickness. An adjusted risk of > 1:270 was considered as a positive screening test. Pregnancy outcome was obtained through karyotyping, outcome questionnaires and examination of the newborn infants. RESULTS: Mean maternal age was 29-4 years and mean gestational age 12.2 weeks. Screening was positive in 230/4523 fetuses (5.1%), when the adjusted risk (mean 1:2649) was > 1:270. Fetal karyotype was abnormal in 23 (0.51%) cases, including twelve with trisomy 21, five trisomy 18, one trisomy 13, one trisomy 10, one monosomy X and two triploidies. For a false positive rate of 4.7%, the sensitivity of this test was 78% in detecting any fetal aneuploidy. Only one out of nine major congenital heart defects in this population was found within the 110 euploid fetuses with increased nuchal translucency thickness (> 2.5 mm). CONCLUSION: Screening for fetal aneuploidy by maternal age and nuchal translucency measurement can be effective in an unselected population. However, our results do not support its effectiveness in the detection of cardiac abnormalities.     

Screening for adverse pregnancy outcome by ductus venosus Doppler at 11-13+6 weeks of gestation

OBJECTIVE: To estimate the independent contribution of abnormal flow in the ductus venosus at 11 to 13+6 weeks of gestation in the prediction of major fetal abnormalities and fetal death. METHODS: This was a prospective assessment of singleton pregnancies by maternal history, serum free beta-hCG, pregnancy-associated plasma protein A (PAPP-A), fetal nuchal translucency thickness, and ductus venosus Doppler. The patients were subdivided into five groups: normal outcome (n=10,120), miscarriage or fetal death (n=185), abnormal karyotype (n=95), and major cardiac (n=20) or noncardiac defect (n=70). Regression analysis was performed to determine the significance of the contribution to adverse outcome of reversed a-wave in the ductus venosus, maternal characteristics, fetal delta nuchal translucency, maternal serum log PAPP-A multiples of the median, and log free beta-hCG multiples of the median. RESULTS: The prevalence of reversed a-wave was significantly higher in the groups with miscarriage or fetal death (10.8%), abnormal karyotype (62.1%), and fetal cardiac defect (25.0%) than in the normal outcome group (3.7%), but not noncardiac defect (4.3%). An adverse outcome was observed in 2.7% of the fetuses with nuchal translucency at or below the 95th centile (in 2.6% of those with normal a-wave and in 7.0% of those with reversed a-wave) and in 19.3% of the fetuses with nuchal translucency above the 95th centile (in 8.9% of those with normal a-wave and in 70.9% of those with reversed a-wave). CONCLUSION: Reversed a-wave is associated with increased risk for chromosomal abnormalities, cardiac defects, and fetal death. However, in about 80% of cases with reversed a-wave, the pregnancy outcome is normal.     

Pregnancy outcome of euploid fetuses with increased nuchal translucency: how bad is the news?

AIMS: The number of fetuses with an abnormal increased first trimester nuchal translucency (NT), but confirmed normal karyotype and anatomy is relatively small and therefore a challenge for prenatal counseling. Universal guidelines are still needed for a systematic work-up, how to decide on the rewarding cut-off for this policy as well as how to counsel patients with an increased NT but with euploid fetuses. The current review aims to address some of these issues. RESULTS: Eleven studies reporting on the pregnancy outcome of 2,128 euploid fetuses with increased NT (>or=3 mm or >or=95 centile) were retrieved by our previously reported literature search. 2.2-10.6% of the fetuses has miscarried and 0.5-15.8% ended in perinatal death. There was an overall rate of 0.5-13% neurodevelopmental problems, and 2-8% of the malformations were undiagnosed before birth, the most common being cardiac anomalies. Nevertheless, 70-90% fetuses had normal outcomes. CONCLUSION: For those euploid fetuses with increased NT>2 MoM or >or=1.5 mm delta NT we recommend a detailed two-step anomaly scan including midgestation fetal echocardiography. Maternal age as well as data on relevant family history and persistence of nuchal edema provides additional relevant information for counseling and planning pregnancy management.     

Should determination of the karyotype be systematic for all malformations detected by obstetrical ultrasound?

OBJECTIVE: The aim of this study was to determine whether karyotyping should be performed for every fetal malformation detected in low risk populations. METHODS: A karyotype was obtained from 428 fetuses examined over a 10-year period after fetal malformation was diagnosed using obstetrical ultrasound. These fetuses were separated into two groups, one with isolated malformations and the other with multiple malformations. The association between each type of malformation and the result of karyotype was evaluated. RESULTS: Forty-eight chromosomal abnormalities were encountered in 428 fetuses (11.2%). The karyotype was abnormal in 32/343 (9.3%) fetuses with isolated malformations and 16/85 (18.8%) fetuses with multiple malformations (p=0.022). The probability of an abnormal karyotype among the group of isolated malformation depended on the anatomical system involved (p<0.001). Our study demonstrated several isolated malformations without chromosomal abnormality (hydronephrosis with high obstruction, unilateral multicystic dysplastic kidney, gastroschisis, intestinal dilatation, meconium peritonitis, cystic adenomatoid malformation, pulmonary sequestration, tumor, vertebral anomaly). CONCLUSION: Each fetus with multiple malformations needs a chromosomal analysis. Within the group of isolated malformations, our study emphasizes that medical maternal history and the type of malformation need to be taken into account before performing a fetal karyotype.     

First-trimester examination of fetal nasal bone in the Chinese population

OBJECTIVES: Absence of the nasal bone in fetuses with trisomy 21 is a potential ultrasound marker for Down syndrome from the first trimester onwards. Racial differences in fetal nasal bone length have been reported. There was no reference range for the first-trimester fetal nasal bone length (NBL) in the Chinese population. METHODS: From January 2002 to February 2005, we investigated the reference range of NBL in 2169 singleton fetuses whose parents were Chinese with normal pregnancy outcome. Ultrasound measurements of NBL were performed on a midsagittal plane at 12-14 weeks' gestation. RESULTS: The nasal bone length measurement showed a significant increase with gestational age (GA) (p < 0.05). A linear relationship between nasal bone length and gestational age (NBL = -3.3462 x GA + 0.627, R(2) = 0.30, p < 0.001) as well as a linear relationship between nasal bone length and crown-rump length (CRL) (NBL = 0.3741 x CRL + 0.284, R(2) = 0.30, P < 0.001) was established. CONCLUSION: The measurement of nasal bone length was feasible in the first trimester. The reference range of NBL in normal Chinese fetuses in the first-trimester of pregnancy was established. This formed a basis for further study on the use of fetal nasal bone measurement in the screening for aneuploidy in the Chinese population.