Antenatal screening for aneuploidy

Trisomy 21 with Maternally Inherited Balanced Translocation (15q;22q) in a Female Fetus: A Rare Case of Probable Interchromosomal Effect

Chromosomal rearrangements can interfere with the disjunction and segregation of other chromosome pairs not involved in the rearrangements, promoting the occurrence of numerical abnormalities in resulting gametes and predisposition to trisomy in offspring. This phenomenon of interference is known as the interchromosomal effect (ICE). Here we report a prenatal case potentially generated by ICE. The first-trimester screening ultrasound of the pregnant woman was normal, but the NIPT indicated a high risk for three copies of chromosome 21, thus suspecting trisomy 21 (T21). After a comprehensive clinical evaluation and genetic counseling, the couple decided to undergo amniocentesis. The prenatal karyotype confirmed T21 but also showed a balanced translocation between the long arm of chromosome 15 (q22) and the long arm of chromosome 22. The parents' karyotypes also showed that the mother had the 15;22 translocation. We reviewed T21 screening methods, and we performed a literature review on ICE, a generally overlooked phenomenon. We observed that ours is the first report of a prenatal case potentially due to ICE derived from the mother. The recurrence risk of aneuploidy in the offspring of translocated individuals is likely slightly increased, but it is not possible to estimate to what extent. In addition to supporting observations, there are still open questions such as, how frequent is ICE? How much is the aneuploidy risk altered by ICE?

Pregnant women's attitudes and decision-making regarding prenatal Down syndrome screening and diagnosis: scale development and validation

Background

Down syndrome is a common chromosomal abnormality and prenatal screening can inform parents of the risk of their baby having Down syndrome. Little research has examined how decisions regarding both Down syndrome screening as well as diagnosis are made among women who are currently pregnant and how their decisions are influenced by their social contexts, specifically family and social media, using mixed methods. The study was to test the validity and reliability of a scale that measures pregnant women’s attitudes and decision-making concerning prenatal Down syndrome screening and diagnosis in urban areas of Taiwan.

Methods

We developed an item pool based on a literature review and in-depth interviews with 30 pregnant women recruited at two district hospitals in urban areas. The item pool was reviewed by a panel of experts and then administered to 300 women who had been pregnant for less than 24 weeks and had not received the Down syndrome screening tests. We used item analysis and exploratory factor analysis to validate the scale and test its reliability.

Results

The initial item pool had 54 items. After the expert review, three items were deleted. After the item analysis, 16 additional items were deleted. Exploratory factor analysis of the remaining items revealed four factors labeled – “Attitudes towards Down syndrome and Screening Tests,” “Important others’ Attitudes towards Down Syndrome,” “Influence of Important Others on Decision-Making,” and “Influence of Social Media on Decision-Making” – and 16 of the remaining items had satisfactory loadings on those factors, explaining 72.0% of the total variance. The Cronbach’s α values of the dimensions ranged between 0.75 and 0.90, demonstrating satisfactory internal reliability.

Conclusions

The scale has satisfactory validity and reliability, and can be used to understand pregnant women’s attitudes and decision-making regarding Down syndrome screening and diagnosis, and to help design tailored consultations for pregnant women in clinical settings.

Comparison and integration of first trimester fetal nuchal translucency and second trimester maternal serum screening for fetal Down syndrome

BACKGROUND

It is uncertain whether first trimester nuchal translucency (NT) is more effective than the well-established second trimester serum screening for fetal Down syndrome or whether their combination works best. We report data from a large multicentre non-interventional trial in which all subjects underwent both first and second trimester screening.

METHODS

All women who attended the obstetric clinic before 15 weeks' gestation were recruited. An ultrasound examination was performed at 10 to 14 weeks to measure the NT. The nuchal measurements were not acted upon unless the fetus showed gross features of hydrops fetalis. All women had serum alpha-fetoprotein (AFP) and human chorionic gonadotrophin (hCG) assay at 15 to 20 weeks. The Down syndrome risk assigned by serum screening was disclosed and amniocentesis was offered if this assigned risk was >or=1:250 or if the women were 35 years and older. The efficacy of different combinations of screening markers was compared.

RESULTS

Between January 1997 and August 2000, 17 590 women were recruited (19% >or=35 years old). After excluding subjects who miscarried, defaulted the serum test and other reasons, 16 237 pregnancies were analysed. Of these, 35 pregnancies were affected by Down syndrome (2.2 cases per 1000 pregnancies). At a false-positive rate of 5%, the detection rate of Down syndrome by NT alone, NT and age, serum hCG, AFP and age, and NT, hCG, AFP and age were 61%, 69%, 73% and 86%, respectively.

CONCLUSION

Integration of NT and second trimester serum AFP and hCG assay yielded the best screening efficacy for Down syndrome.

Trisomy 21. Second-trimester ultrasound

Not every aspect of sonographic examination reveals karyotypic abnormalities. Ultrasound examination of a fetus with trisomy 21 generally reveals normal amniotic fluid, normal placentation, and normal fetal growth. In addition, other chromosomal abnormalities have many of the same sonographic findings as Down syndrome, and many findings have a large overlap with phenotypically normal fetuses. The importance of second-trimester ultrasound screening for Down syndrome has remained great because of its ease of use and relative effectiveness. Trained sonographers can adjust the relative risk for trisomy 21 and alter the need for genetic amniocentesis. It is important that parents understand the limitations of a screening test and the risks and benefits of possible subsequent confirmatory testing. If a major structural abnormality is identified on ultrasound, karyotype determination should be considered. Nuchal thickness in the first or second trimester remains the most clinically useful marker for trisomy 21. The predictive value of all the markers depends on the population studied and can be modified by a host of biochemical markers and historical factors. If fetal karyotype analysis could be performed without sampling through the uterus, prenatal diagnosis could be offered to all pregnant women, and screening would be unnecessary. Despite its limitations, ultrasound will have an important role in prenatal diagnosis at least until isolating and testing fetal cells from maternal blood or other sources becomes practical and widely available. Whether used alone or in conjunction with additional biochemical or molecular serum markers, ultrasound is an important and powerful tool in prenatal genetic evaluation.

Screening for aneuploidy

Over the past 15 years, biochemical screening for chromosomal abnormalities, particularly Down's syndrome, has advanced from being extremely naive, to now somewhat more sophisticated. Sensitivities have gone from 20% to 60-70%. Considerable work is still required to not only increase the sensitivity, but also the specificity to keep health care costs down.

Early transvaginal measurement of cephalic index for the detection of down syndrome fetuses

OBJECTIVE

The aim of this study was to produce normal cephalic index values by transvaginal scan early in pregnancy and to evaluate the screening utility of this measurement for the identification of fetuses at risk for Down syndrome.

METHOD

In this prospective cross-sectional study, transvaginal high-resolution sonography was performed between 9 and 16 weeks of gestation in 1,087 euploid fetuses and 36 Down syndrome fetuses. Measurements of the cephalic index, calculated as the ratio biparietal diameter/occipito-frontal diameter, were plotted against gestational age.

RESULTS

The cephalic index was found to show fairly constant values throughout the period evaluated. The best correlation with gestational age was described by a linear correlation. All the measurements obtained in Down syndrome fetuses were within the normal ranges.

CONCLUSION

Our data show that in early pregnancy the cephalic index cannot be considered a useful tool in the detection of fetuses at risk for Down syndrome.