Genetic Counseling and Prenatal Diagnosis of Triploidy During the Second Trimester of Pregnancy

An expert opinion on rescuing atypically pronucleated human zygotes by molecular genetic fertilization checks in IVF

IVF laboratories routinely adopt morphological pronuclear assessment at the zygote stage to identify abnormally fertilized embryos deemed unsuitable for clinical use. In essence, this is a pseudo-genetic test for ploidy motivated by the notion that biparental diploidy is required for normal human life and abnormal ploidy will lead to either failed implantation, miscarriage, or significant pregnancy complications, including molar pregnancy and chorionic carcinoma. Here, we review the literature associated with ploidy assessment of human embryos derived from zygotes displaying a pronuclear configuration other than the canonical two, and the related pregnancy outcome following transfer. We highlight that pronuclear assessment, although associated with aberrant ploidy outcomes, has a low specificity in the prediction of abnormal ploidy status in the developing embryo, while embryos deemed abnormally fertilized can yield healthy pregnancies. Therefore, this universal strategy of pronuclear assessment invariably leads to incorrect classification of over 50% of blastocysts derived from atypically pronucleated zygotes, and the systematic disposal of potentially viable embryos in IVF. To overcome this limitation of current practice, we discuss the new preimplantation genetic testing technologies that enable accurate identification of the ploidy status of preimplantation embryos and suggest a progress from morphology-based checks to molecular fertilization check as the new gold standard. This alternative molecular fertilization checking represents a possible non-incremental and controversy-free improvement to live birth rates in IVF as it adds to the pool of viable embryos available for transfer. This is especially important for the purposes of 'family building' or for poor-prognosis IVF patients where embryo numbers are often limited.

Polyploidy Phenomenon as a Cause of Early Miscarriages in Abortion Materials

Objectives

Chromosomal abnormalities are an important cause of especially early miscarriages. The aim of this study was to analyze the chromosomal aberrations and determine the frequencies of numerical and structural chromosome abnormalities in spontaneous abortion materials.

Methods

This was a prospective research and ninety two abortion samples obtained from women who had one or more miscarriages were included in the study. Conventional karyotype analysis was performed on each sample to identify possible chromosomal abnormalities.

Results

By karyotype analysis, 11 polyploidy cases, (9 triploids and 2 tetraploids), 8 trisomies (one of which was mosaic), 2 monosomies (monosomy X), 1 isochromosome, 1 Xq deletion, and 4 translocations were detected in abortion materials. Isochromosome and Xq deletion cases were also mosaic. In addition, five polymorphic variants were revealed. We found higher paternal age in polyploidy cases.

Conclusion

The most common anomaly we found in abortion materials was polyploidy. This was followed by aneuploidy (trisomy and monosomy). Polyploidy (triploidy or tetraploidy) emerged as an important cause in cases of spontaneous abortion. Paternal age may be associated with polyploidy especially triploidy.

First Trimester Screening Tests Pregnancy and Trisomy 13 Syndrome, Sex Chromosome Aneuploidy in Iran: A Cross-Sectional Study

BACKGROUND

Trisomy 13 (T13) and sex chromosome aneuploidies (SCA) are the vital causes of congenital malformations. This study was performed to identify the T13 and SCA with screening tests in the first trimester of pregnancy.

MATERIALS AND METHODS

In this cross-sectional study, first-trimester combined screening was conducted on 2100 pregnant women referred to Narges Genetics Laboratory, Ahvaz, Iran. Evaluating the first trimester screening tests, including nuchal translucency (NT), crown-rump length (CRL) and pregnancy-associated plasma protein-A (PAPP-A), and free beta of human chorionic gonadotropin (fβhCG) was performed. For a definitive diagnosis of T13 and SCA syndrome, fetal karyotype was evaluated.

RESULTS

The average NT and CRL in high-risk group for T13 were 5.96 mm and 61.7 mm respectively and in high-risk groups for SCA were 3.7 mm and 75.9 mm, respectively. Significant correlation was observed among NT, CRL and T13, SCA (P<0.05). The average serum fβhCG and PAAP-A levels in high-risk group for T13 were 0.42 and 0.31, respectively. Significant correlation was observed between decrease fβhCG, PAPP-A and T13 levels and increase fβhCG levels and SCA levels (P<0.05). No Significant correlation was observed between PAPP-A levels and SCA levels (P>0.05).

CONCLUSION

Using special software and karyotype testing, the prenatal screening tests based on the maternal age and gestational age in the first trimester of pregnancy may determine the major risk of fetal chromosomal abnormalities.

Prenatal Diagnosis of Triploidy in Fetus with Unexpected Chromosomal Translocation of Maternal Origin

Triploidy is a lethal chromosomal abnormality. Fetuses with triploid condition have a tendency to die in early conception and very few survive to term. In this study, we report the prenatal diagnosis of fetal triploidy with unexpected chromosomal translocation. A 27 years old women was referred to our clinical cytogenetic department due to history of previous conceptus with intrauterine growth retardation at 21-22 weeks of gestation and in present pregnancy, the quadruple marker screen test had suggested a high risk for Trisomy 18 with the risk >1:50. The study was performed on the amniotic fluid and peripheral blood samples received at the clinical cytogenetics department. The interphase FISH and conventional karyotype methods were followed. The prenatal diagnosis using an amniotic fluid sample found a triploid fetus with unexpected balanced chromosomal translocation: 69, XXX,t(2;9)(q11.2;p22)x2. Later the origin of translocation was confirmed by parental chromosomal study. Cytogenetic analysis showed the presence of translocation involving chromosome 2 and 9 in the mother which confirms the maternal origin of translocation in fetal triploidy. Prenatal diagnosis of fetal triploidy with balanced translocation of maternal origin is a rare finding. In present study, the triploidy arises from the failure to expel the second polar body. It is important to perform prenatal fetal imaging with ultrasound at 18-22 weeks to identify any fetal anomalies or intrauterine growth retardation which is associated with triploidy.

Prenatal diagnosis of syndromic alobar holoprosencephaly associated with digynic triploidy fetus

Holoprosencephaly (HPE) is a dramatic human brain malformation sequence with an extreme variable phenotypic spectrum and genetic heterogeneity, variable degree of severity and unknown etiology, in many cases. HPE is classified into syndromic, chromosomal, and non-syndromic, non-chromosomal. The most cases of HPE are syndromic. We present an atypical case of syndromic alobar HPE associated with digynic triploidy fetus, prenatally diagnosed, early at 18 weeks of gestation, by ultrasound (US) and complex genetic investigations. The US examination was performed with a specialized US machine, General Electric Voluson E10 OLED BT18, using two-dimensional (2D) scanning, three-dimensional (3D) image reconstruction, four-dimensional (4D) spatiotemporal image methodology and the highest power Doppler US technology. A detailed US examination of the fetus revealed several major abnormalities of the fetal head and severe facial malformations. Based on the antenatal US findings, the fetus was diagnosed with alobar HPE. After a careful examination and genetic counseling, additional cytogenetic investigations and molecular genetic analyses were performed, which revealed an abnormal number of 69 chromosomes, digynic triploidy (69,XXY). Two days later, the parents choose to interrupt the current gestation because of major fetal malformations. The pathological examination of the embryo reaffirmed the antenatal diagnostics.

Recurrent fetal triploidy: is there a genetic cause?

Triploidy is currently understood as a sporadic genetic disorder, with no recognisable risk of recurrence nor identifiable risk factors. In cases of triploidy, chances of thriving through the second trimester of fetal development are very slim, with most of these pregnancies ending as early miscarriage. We report a case of repeated triploid pregnancies in the same woman, from different fathers, achieving the second trimester of pregnancy; elective termination was decided in both cases, after an amniocentesis revealing a triploid karyotype. Both triploid pregnancies are described and compared; prenatal laboratorial markers, sonographic features, clinical course and pathological findings are analysed and matched with fetal autopsy and placental pathological study. Reported findings strongly point to recurrent triploidy of maternal origin, and so the possibility of a genetic predisposition should be considered. Investigation is required to assess the presence of an underlying genetic mechanism in this setting, thus enabling a better genetic/obstetric counselling.

Screening of triploid with low-coverage whole-genome sequencing by a single-nucleotide polymorphism-based test in miscarriage tissue

PURPOSE

To establish a single-nucleotide polymorphism-based analysis (SBA) method to identify triploidy in the miscarriage tissue by using low-coverage whole-genome sequencing (LC-WGS).

METHODS

The method was established by fitting a quadratic curve model by counting the distribution of three heterozygous mutation content intervals. The triploid test result was mainly determined by the opening direction and the axis of symmetry of the quadratic curve, and Z test between the same batch samples was also used for auxiliary judgment.

RESULTS

Two hundred thirteen diploid samples and 8 triploid samples were used for establishment of the analytical method and 203 unknown samples were used for blind testing. In the blind testing, we found 2 cases positive for triploidy. After chromosome microarray analysis (CMA) and mass spectrometry verification, we found that both samples were true positives. We randomly selected 5 samples from the negative samples for mass spectrometry verification, and the results showed that these samples were all true negatives.

CONCLUSIONS

Our method achieved accurate detection of triploidy in the miscarriage tissue and has the potential to detect more chromosomal abnormality types such as uniparental disomy (UPD) using a single LC-WGS approach.