Ersttrimester Ultraschall Screening für Down-Syndrom
Zusammenfassung der Projektergebnisse
Effective screening for trisomy 21 is provided in the first-trimester of pregnancy by a combination of maternal age, fetal nuchal translucency (NT) thickness and maternal serum free ƒÀ-human chorionic gonadotropin (ƒÀ-HCG) and pregnancy associated plasma protein-A (PAPP-A) with a detection rate of about 90% for a false positive rate of 5%. Next to increased NT, chromosomal abnormalities are associated with a pattern of characteristic sonographic findings in the first-trimester. Extensive studies showed that assessment of the frontomaxillary facial (FMF) angle and the fetal nasal bone (presence/absence) improves the performance of first-trimester screening for trisomy 21. Inclusion of these additional markers in first-trimester screening improves the detection rate up to 95%. Assessment of ductus venosus waveform reveals additional information as an abnormal flow pattern (reversed a-wave) is associated with increased risk for chromosomal abnormalities, cardiac defects, and fetal death. In fetuses with increased NT, the prevalence of abnormal flow in the ductus venosus is higher in those with cardiac defects than in those with no cardiac defects. In the majority of fetuses with cardiac defects and normal NT, in contrast to those with increased NT, the flow pattern in the ductus venosus is normal. The prevalence of reversed a-wave in fetal deaths was three times higher than in the normal outcome group, irrespective of fetal NT. However, in approximately 80% of cases with reversed a-wave, the pregnancy outcome is normal as 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 NT. In twins, reversed a-wave in the ductus venosus at 11+0 to 13+6 weeks of gestation is associated with increased risk for aneuploidies, miscarriage, and development of severe twin-twin transfusion syndrome. However, in about 75% of dichorionic twins and 40% of monochorionic twins with reversed a-wave, the pregnancy outcome is normal. Low serum PAPP-A at 11+0 to 13+6 weeks is associated with increased risk of chromosomal abnormalities like Trisomy 21, 13 and 18, but also observed in euploid pregnancies that subsequently develop early-preeclampsia (PE). In contrast to chromosomal abnormalities, in early-PE maternal age, fetal NT and serum free s-hCG are not significantly different from controls. Another distinguishing factor between early-PE and trisomy 21 was uterine artery pulsatility index (PI) which was increased in the former and was normal in the latter. The uterine artery PI at 11+0 to 13+6 weeks may be useful in distinguishing between low PAPP-A due to trisomy 21 and early PE. Assessment of the individual components of screening by means of inclusion of uterine artery PI is likely to improve the patient-specific management of pregnancies with low PAPP-A.
