Abnormal flow in the ductus venosus at 11–13+6 weeks of gestation is associated with increased risk for trisomy 21 and other chromosomal abnormalities.1–8 In euploid fetuses, abnormal flow in the ductus venosus is associated with an increased risk for cardiac defects.3,4,6,9–13 However, most studies examining such an associated are confined to fetuses with increased nuchal translucency thickness. There is also some evidence that abnormal flow in the ductus venosus is associated with an increased risk for fetal death. A first-trimester screening study reported that the prevalence of abnormal flow in the ductus venosus in the cases resulting in fetal death was 22.2% (four of 18) compared with 5.9% (61 of 1,041) in the normal outcome group.6 However, abnormal flow was observed in four of the eight fetal deaths presenting with nuchal translucency above the 95th centile and in none of the 10 with normal nuchal translucency.
A case–control study of fetuses with nuchal translucency below the 95th centile reported that in 10 of 42 (23.8%) cases with abnormal flow in the ductus venosus there was an adverse outcome, including perinatal death and chromosomal, cardiac or noncardiac abnormalities.14 In contrast, an adverse outcome was observed in only one of 83 (1.2%) controls with normal flow in the ductus venosus.
The aim of this screening study involving more than 10,000 pregnancies, in which maternal characteristics, serum free β-hCG and pregnancy-associated plasma protein A (PAPP-A), and fetal nuchal translucency thickness as well as the flow in the fetal ductus venosus were assessed at 11 to 13+6 weeks of gestation, was to estimate the independent contribution of abnormal flow in the ductus venosus in the prediction of major fetal abnormalities and fetal death.
MATERIALS AND METHODS
This was a prospective screening study for trisomy 21 in singleton pregnancies by a combination of maternal age, fetal nuchal translucency thickness, and maternal serum free β-hCG and PAPP-A in a one-stop-clinic for first trimester assessment of risk at 11 to 13+6 weeks of gestation.15 Transabdominal ultrasound examination was performed to diagnose any major fetal defects and for measurement of fetal crown-rump length (CRL) and nuchal translucency thickness.16 Ductus venosus blood flow velocity waveforms were also routinely obtained by ultrasonographers who had received the appropriate Fetal Medicine Foundation Certificate of Competence in this assessment. Automated machines that provide reproducible results within 30 minutes were used to measure PAPP-A and free β-hCG (Delfia Express System, Perkin Elmer, Waltham, MA). Patients were asked to complete a questionnaire on maternal age, ethnic origin (White, Black, Indian or Pakistani, Chinese, or Japanese, and Mixed), cigarette smoking during pregnancy (yes or no), parity (parous or nulliparous if no delivery beyond 23 weeks), and mode of conception (spontaneous, including those receiving ovulation induction drugs, or assisted reproduction by in vitro fertilization [IVF]). The maternal weight and height were measured and the body mass index (BMI) was calculated in kilograms per square meter. Written informed consent was obtained from each patient participating in the study, which was approved by King’s College Hospital Research Ethics Committee.
Maternal demographic characteristics, ultrasonographic measurements, and biochemical results were recorded in a computer database. Karyotype results, details on fetal abnormalities diagnosed during subsequent ultrasound examinations or postnatally, and pregnancy outcomes were obtained from cytogenetic laboratories, hospital maternity records, the patients themselves, or their general medical practitioners, and these data were added into our database as soon as they became available.
In the ductus venosus studies the following criteria were fulfilled17: 1) the examinations were undertaken during fetal quiescence; 2) the magnification of the image was such that the fetal thorax and abdomen occupied the whole screen; 3) a right ventral mid sagittal view of the fetal trunk was obtained and color flow mapping was used to demonstrate the umbilical vein, ductus venosus, and fetal heart; 4) the pulsed Doppler sample was small (0.5–1.0 mm) to avoid contamination from the adjacent veins, and it was placed in the yellowish aliasing area, which is the portion immediately above the umbilical sinus; 5) the insonation angle was less than 30 degrees; 6) the filter was set at a low frequency (50–70 Hz) to allow visualization of the whole waveform; and 7) the sweep speed was high (2–3 cm/s) so that the waveforms were widely spread, allowing better assessment of the a-wave. Waveforms were assessed qualitatively and considered to be abnormal if the a-wave was reversed.
A search of the database was done to identify all singleton pregnancies in which first trimester combined screening was carried out from March 2006 to May 2007. The patients were subdivided into 1) a normal outcome group of live births with no obvious chromosomal abnormalities or fetal defects; 2) miscarriage before 24 weeks of gestation or fetal death at or after 24 weeks; 3) abnormal karyotype; and 4) fetal defect. In the last group we included only cases in which the defect would result in severe handicap or the need for surgical or medical treatment. We did not include conditions like polydactyly or mild ventriculomegaly or pyelectasia.
Analysis of variance (with the Bonferroni post-hoc test) and χ2 were used to compare the demographic characteristics of the normal outcome group with each of the adverse outcome groups. The measured free β-hCG and PAPP-A were converted into a multiples of the median (MoM) for gestational age adjusted for maternal weight, ethnicity, smoking status, method of conception, parity, and machine for the assays.18 The distributions of PAPP-A MoM and free β-hCG MoM were made Gaussian after logarithmic transformation. The measured nuchal translucency was expressed as a difference from the normal mean for gestation (delta value).19
Comparisons between each of the pregnancy outcomes and the normal outcome group was by analysis of variance (with Bonferroni post-hoc test) for log PAPP-A MoM and log free β-hCG MoM, Kruskal-Wallis test (with Dunn’s post-hoc test) for the fetal delta nuchal translucency and the χ2 and Fisher exact test for the prevalence of reversed a-wave. Multiple logistic regression analysis in the whole population was used to determine the significant contributors to reversed a-wave in the fetal ductus venosus from maternal characteristics, different outcome groups, fetal CRL, delta nuchal translucency, maternal serum log MoM PAPP-A, and log MoM free β-hCG. Similarly, multiple regression analysis was performed to determine the significance of the contribution to fetal death, fetal chromosomal abnormality or defect of reversed a-wave, maternal characteristics, fetal CRL, delta nuchal translucency, maternal serum log MoM PAPP-A, and log MoM free β-hCG.
During the study period, first-trimester combined screening was carried out in 11,093 cases, and in 11,005 (99.2%) of these there was successful visualization of the ductus venosus and assessment of the a-wave. In 493 cases there was loss to follow-up, and 22 women chose to have pregnancy termination for psychosocial indications. In the remaining 10,490 pregnancies, the median maternal age was 32 (range 16–49) years, the median CRL was 63.8 (range 45–84) mm and the median delta nuchal translucency thickness was 0.07 (range –0.9 to 11.2) mm.
There were 10,120 pregnancies resulting in live births with no obvious chromosomal abnormalities or fetal defects (normal outcome group). In 185 pregnancies there was miscarriage before 24 weeks or fetal death at or after 24 weeks (fetal death group). In 95 cases the fetal karyotype, determined by chorionic villous sampling, amniocentesis, or postnatally, was abnormal including trisomy 21 in 45, trisomy 18 or 13 in 28, and other defects (triploidy, sex chromosome aneuploidies, deletions, translocations, mosaicism) in 22. Fetal defects were detected in 90 cases, including 20 with cardiac defects (coarctation of the aorta in six, Ebstein anomaly in three, atrioventricular or ventricular septal defect in three, double-outlet right ventricle in two, transposition of the great arteries in two, and one case each of tetralogy of Fallot, pulmonary atresia, pulmonary stenosis, and Scimitar syndrome) and 70 with noncardiac defects (ventriculomegaly of more than 12 mm in five, agenesis of the vermis in one, neural tube defects in three, facial cleft in nine, diaphragmatic hernia or cystic adenomatoid malformation of the lungs in eight, esophageal or duodenal atresia in two, abdominal wall defect in six, obstructive uropathy multicystic kidneys, polycystic kidneys or renal agenesis in 20, talipes in 13, skeletal dysplasia in 3). The demographic characteristics of the outcome groups are summarized in Table 1.
Reversed a-wave was observed in 458 (4.4%) of the fetuses, and the prevalence was significantly higher in the groups with miscarriage or fetal death (10.8%), abnormal karyotype (62.1%), and fetal cardiac defect (25.0%), but not noncardiac defect (4.3%) than in the normal outcome group (3.7%) (Table 2). There were no significant differences between miscarriages and late fetal deaths in prevalence of reversed a-wave (P=.907), log MoM PAPP-A (P=.713), or log MoM free β-hCG (P=.539), and therefore the data of the two subgroups were combined.
Logistic regression analysis demonstrated that significant contribution to reversed a-wave was provided by the different outcome groups (fetal death, odds ratio [OR] 2.222; 95% confidence interval [CI] 1.359–3.635; P<.001; abnormal karyotype OR 17.514; 95% CI 9.752–31.455; P<.001; fetal cardiac defect OR 6.793; 95% CI 2.296–20.104; P<.001), but also by fetal CRL (OR 0.967; 95% CI 0.954–0.980; P<.001), and delta nuchal translucency (OR 1.387; 95% CI 1.183–1.627; P<.001), Black ethnicity (OR 2.425; 95% CI 1.952–3.014; P<.001) and serum log MoM PAPP-A (OR 0.434; 95% CI 0.295–0.640; P<.001) but not maternal age (P=.118), BMI (P=.748), smoking (P=.708), serum log MoM free β-hCG (P=.414) or fetal noncardiac defects (P=.997).
An adverse outcome (fetal death, abnormal karyotype, or fetal defect) occurred in 370 (3.5%) of the 10,490 cases. Logistic regression analysis demonstrated that significant contribution to adverse outcome was provided by reversed a-wave (OR 3.648; 95% CI 2.639–5.042; P<.001), fetal delta nuchal translucency (OR 2.929; 95% CI 2.473–3.468; P<.001), maternal serum log MoM PAPP-A (OR 0.180; 95% CI 0.118–0.275; P<.001), Black ethnicity (OR 2.027; 95% CI 1.560–2.634; P<.001) and maternal BMI (OR 1.024; 95% CI 1.003–1.045; P<.025), but not maternal age (P=.051), smoking (P=.616), serum log MoM free β-hCG (P=.529), or fetal CRL (P=.885).
Reversed a-wave was observed in 3.7% (372 of 9,976) of the fetuses with nuchal translucency at or below the 95th centile and in 16.7% (86 of 514) with nuchal translucency above the 95th centile (Table 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).
Reversed a-wave in the fetal ductus venosus was observed in 64.4% of fetuses with trisomy 21, 67.9% of fetuses with trisomies 18 or 13, and 50% of fetuses with other chromosomal abnormalities. All three groups were associated with increased nuchal translucency and decreased PAPP-A. In trisomy 21, free β-hCG was increased; in trisomies 18 and 13 it was decreased, and in the other chromosomal abnormalities it was not significantly different from normal (Table 2).
Logistic regression analysis demonstrated that significant contribution to fetal chromosomal abnormality was provided by reversed a-wave, as well as maternal age, fetal delta nuchal translucency and maternal serum log MoM PAPP-A, but not maternal serum log MoM free β-hCG, ethnicity, BMI, smoking, or fetal CRL (Table 4). The apparent lack of significant contribution from log MoM free β-hCG is because in this analysis we considered all chromosomal abnormalities together; in trisomy 21 the levels were significantly increased, and in trisomies 18 and 13 they were decreased.
Reversed a-wave was observed in 25.0% of fetuses with cardiac defects. Logistic regression analysis demonstrated that significant contribution to fetal cardiac defect was provided by reversed a-wave in the fetal ductus venosus and fetal delta nuchal translucency, but not maternal age, ethnicity, BMI, smoking, log MoM PAPP-A, log MoM free β-hCG, or fetal CRL (Table 4).
The prevalence of reversed a-wave in fetuses with noncardiac defects was not significantly higher than in the normal outcome group (4.3% compared with 3.7%, P=.744). Logistic regression analysis demonstrated that significant contribution to fetal noncardiac defects was provided by fetal delta nuchal translucency, but not reversed a-wave, maternal age, ethnicity, BMI, smoking, log MoM PAPP-A, log MoM free β-hCG, or fetal CRL (Table 4).
Logistic regression analysis demonstrated that significant contribution to fetal death was provided by reversed a-wave in the fetal ductus venosus, as well as Black ethnicity, BMI, and maternal serum log MoM PAPP-A, but not maternal age, smoking, serum log MoM free β-hCG, fetal delta nuchal translucency, or CRL (Table 4).
The patient-specific risk for fetal death (%) was calculated from the formula: odds/(1+odds), where odds=eY. Y was derived from the multiple regression analysis above: Y=–5.324+(0.807 if reversed a-wave, 0 if normal a-wave)+0.033×BMI in Kg/m2+(1.144 if Black, 0 if other ethnic origin)–1.238×log MoM PAPP-A; R2=0.062, P<.001. Figure 1 illustrates how the PAPP-A–related risk of fetal death in women of Black and White ethnicity is modified by the findings of the fetal ductus venosus Doppler.
At 11–13+6 weeks of gestation, approximately 4% of fetuses demonstrate reversed a-wave in the flow velocity waveform from the ductus venosus. This abnormal flow pattern is associated with increased risk for chromosomal abnormalities, cardiac defects, and fetal death.
The finding that the risk for chromosomal abnormalities is increased with maternal age, fetal nuchal translucency, altered concentrations of maternal serum PAPP-A, and free β-hCG is compatible with the results of extensive previous studies.15,16,20 In addition, we observed reversed a-wave in the ductus venosus in about 65% of fetuses with trisomies 21, 18, and 13 and in 50% of those with other abnormalities. In eight previous studies on a combined total of 10,945 pregnancies, abnormal flow in the fetal ductus venosus was observed in 5% (range 1.7–13.0%) of euploid fetuses and in 72.1% (range 38.3–100%) of the 210 with trisomy 21.1–8 The incorporation of flow in the ductus venosus in the risk algorithms for first-trimester screening of chromosomal abnormalities is the subject of a separate study.
The findings that the prevalence of major cardiac defects increased with fetal nuchal translucency and was higher in those with reversed a-wave than in those with normal ductus venosus flow are compatible with previous reports.3,4,6,9–13,21,22 A major limitation of our study was the method of diagnosing or excluding cardiac defects, which was based on antenatal ultrasonographic assessment or neonatal clinical examination. Ideally the antenatal findings of either absence or presence of a cardiac defect should have been validated by specialist examination of all infants that were liveborn and by postmortem examination in all cases of pregnancy termination or perinatal death. This methodologic problem is the most likely explanation for the overall prevalence of major cardiac defects (0.2%) being lower than the estimated 0.5% in chromosomally normal fetuses at this gestation.23 Despite this limitation, the proportion of our fetuses with cardiac defects presenting with nuchal translucency above the 95th centile (eight of 20) was similar to the results of a meta-analysis, which reported that in 37% of euploid fetuses with cardiac defects the fetal nuchal translucency were above the 95th centile.22
In fetuses with increased nuchal translucency, the prevalence of abnormal flow in the ductus venosus is higher in those with cardiac defects than in those with no cardiac defects. In our euploid fetuses with nuchal translucency above the 95th centile, reversed a-wave was observed in 62.5% (five of eight) fetuses with cardiac defects, compared with 6.0% (25 of 415) in the normal outcome group. In seven previous studies on a combined total of 600 euploid fetuses with nuchal translucency above the 95th centile, there were 29 cases of cardiac defects, and abnormal flow in the ductus venosus was observed in 96.6% (range 75–100%) of fetuses with cardiac defects, compared with 18.2% (range 0–40%) in those with no cardiac defects.3,4,6,9–12 In another study of 191 euploid fetuses with nuchal translucency above the 99th centile, including 16 with cardiac defects, abnormal flow in the ductus venosus was observed in 68.8% of fetuses with cardiac defects, compared with 22.9% in those with no cardiac defects.13 In the majority of fetuses with cardiac defects and normal nuchal translucency, in contrast to those with increased nuchal translucency, the flow pattern in the ductus venosus is normal. Abnormal flow in the ductus was not observed in any of the 12 such cases in our study or the four cases in the combined data from two previous studies.6,12 The consequence of this finding is that despite previous expectations,13 first-trimester screening by Doppler of the ductus venosus is unlikely to improve the overall detection rate of cardiac defects achieved by screening with nuchal translucency alone.
The finding that the prevalence of noncardiac defects increased with fetal nuchal translucency thickness is compatible with the results of previous studies showing that with increasing fetal nuchal translucency thickness there is an increase in the prevalence of a wide variety of fetal malformations, dysplasias, deformations, disruptions, and genetic syndromes.24 Although the prevalence of reversed a-wave increased with increasing fetal nuchal translucency thickness, the prevalence of reversed a-wave in fetuses with noncardiac defects was not significantly higher than in the normal outcome group. Similarly, in one previous screening study by Toyama et al,6 abnormal flow in the ductus venosus was observed in 11.1% (one of nine) of fetuses with noncardiac defects, which was not significantly higher than the prevalence of 5.9% (61 of 1,041) in the normal outcome group.
The prevalence of reversed a-wave in fetal deaths was three times higher than in the normal outcome group, irrespective of fetal nuchal translucency thickness. In a previous smaller screening study, the prevalence of abnormal flow in the ductus venosus was similarly higher in the cases resulting in fetal death than in the normal outcome group (22.2% compared with 5.9%), but in all their fetal deaths with abnormal flow there was increased nuchal translucency thickness.6 We found that additional independent risk factors for fetal death included low maternal serum PAPP-A and Black ethnicity. The association between low PAPP-A, which presumably implies impaired placentation, and both early and late fetal death is compatible with the results of previous studies.25–30 As demonstrated in our study, this PAPP-A–related patient-specific risk for fetal death can be modified by the results of the assessment of the fetal ductus venosus. In the second and third trimesters of pregnancy, abnormal flow in the ductus venosus is associated with fetal compromise,31 and this seems to be true also for the first trimester.
There is a theoretical risk of thermal damage to the developing fetus from the use of color and pulsed Doppler examination. However, such theoretical risk applies only to transvaginal ultrasonography before 10 weeks, and in any case there is no epidemiologic or other evidence to support such assertion.32 In our study, the ultrasound examinations were performed transabdominally after 11 weeks, and we used the “as low as reasonably achievable” principle, with output settings of the machines resulting in thermal index and mechanical index values below 0.6.
Reversed a-wave in the ductus venosus is associated with increased risk for chromosomal abnormalities, cardiac defects, and fetal death. However, in approximately 80% of cases with reversed a-wave, the pregnancy outcome is normal. The rate of adverse outcome is not only associated with reversed a-wave but also with certain maternal characteristics, altered levels of serum metabolites, and fetal nuchal translucency. The rate of adverse outcome in fetuses with reversed a-wave increases from less than 10% in those with normal nuchal translucency to more than 70% in those with high nuchal translucency.
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