Second-trimester diagnosis of triploidy: a series of four cases

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.

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

Introduction:

Triploidy is a lethal chromosomal numeric abnormality, characterized on extra haploid set of chromosomes. It occurs in 2 to 3% of conceptuses and accounts for approximately 20% of chromosomally abnormal first-trimester miscarriages. As such, triploidy is estimated to occur in 1 of 3,500 pregnancies at 12 weeks’, 1 in 30,000 at 16 weeks’, and 1 in 250,000 at 20 weeks’ gestation.

Case report:

We present a case of second-trimester triploidy diagnosed prenataly at our center. 28-years-old gravida with a first spontaneous pregnancy had early gestational hypertension. Ultrasound examination in 14^6/7 weeks’ gestation revealed asymmetric intrauterine growth retardation. We recommended biochemical maternal serum screening during second trimester of pregnancy (AFP, HCG, uE3). Result of biochemical screening was indication for cytogenetic analysis from amniotic fluid cells and we recommended early amniocentesis in 15^6/7 weeks’ gestation. Result showed abnormal karyotype of the fetus (69,XXX triploidy), and DNA analysis confirmed Type-2 Diginy. Parents decided to terminate this pregnancy, and it was done at 22 weeks’ gestation.

Conclusion:

We emphasize the importance of non-invasive prenatal exminationes-biochemical serum screening during second trimester of pregnancy, and ultrasound examinations in prenatal screening of syndroma Down and other chromosomal abnormalities.

Non-invasive prenatal testing for fetal chromosome abnormalities: review of clinical and ethical issues

Genomics-based non-invasive prenatal screening using cell-free DNA (cfDNA screening) was proposed to reduce the number of invasive procedures in current prenatal diagnosis for fetal aneuploidies. We review here the clinical and ethical issues of cfDNA screening. To date, it is not clear how cfDNA screening is going to impact the performances of clinical prenatal diagnosis and how it could be incorporated in real life. The direct marketing to users may have facilitated the early introduction of cfDNA screening into clinical practice despite limited evidence-based independent research data supporting this rapid shift. There is a need to address the most important ethical, legal, and social issues before its implementation in a mass setting. Its introduction might worsen current tendencies to neglect the reproductive autonomy of pregnant women.

Identification of trisomy 18, trisomy 13, and Down syndrome from maternal plasma

Current prenatal diagnosis for fetal aneuploidies (including trisomy 21 [T21]) generally relies on an initial biochemical serum-based noninvasive prenatal testing (NIPT) after which women who are deemed to be at high risk are offered an invasive confirmatory test (amniocentesis or chorionic villi sampling for a fetal karyotype), which is associated with a risk of fetal miscarriage. Recently, genomics-based NIPT (gNIPT) was proposed for the analysis of fetal genomic DNA circulating in maternal blood. The diffusion of this technology in routine prenatal care could be a major breakthrough in prenatal diagnosis, since initial research studies suggest that this novel approach could be very effective and could reduce substantially the number of invasive procedures. However, the limitations of gNIPT may be underappreciated. In this review, we examine currently published literature on gNIPT to highlight advantages and limitations. At this time, the performance of gNIPT is relatively well-documented only in high-risk pregnancies for T21 and trisomy 18. This additional screening test may be an option for women classified as high-risk of aneuploidy who wish to avoid invasive diagnostic tests, but it is crucial that providers carefully counsel patients about the test's advantages and limitations. The gNIPT is currently not recommended as a first-tier prenatal screening test for T21. Since gNIPT is not considered as a diagnostic test, a positive gNIPT result should always be confirmed by an invasive test, such as amniocentesis or chorionic villus sampling. Validation studies are needed to optimally introduce this technology into the existing routine workflow of prenatal care.

Chromosome aberrations in a large series of spontaneous miscarriages in the German population and review of the literature

Background

In a review of the literature in 2000 the different cytogenetic aspects of spontaneous miscarriages were well documented. This review also included the spontaneous miscarriage results of one large German study published in 1990. However, to our knowledge there are no new data on spontaneous miscarriages in the German population. Therefore, the aim of the present retrospective large study was to find out the incidence and types of chromosome aberrations in an unselected series of spontaneous miscarriages in the German population, and whether our more recent results were different to data published previously. In case of culture failure we implemented a quantitative fluorescent polymerase chain reaction (QF-PCR) for chromosomes 13, 18, 21, X and Y.

Results

In the present German retrospective study cytogenetic analysis (CA) was attempted on 534 spontaneous miscarriages between weeks 7 and 34 of gestation, being successful in 73% (390/534) of them. Two hundred and thirty-seven of the cases (61%, 237/390) were chromosomally abnormal. Trisomy was the most common chromosome aberration and accounted for 53% (125/237) of the aberrant karyotypes. A multiple aneuploidy was observed in 7% (17/237) of the aberrant karyotypes. Chromosomes 16, 22, 15 and 21 were found most frequently involved in aneuploidies. Fifty-four cases (23%, 54/237) with a polyploidy were found in the present study. Single unbalanced structural chromosome aberrations accounted for 4% (10/237) of the aberrant karyotypes. Eleven samples (5%, 11/237) displayed a variety of numerical and/or structural chromosome aberrations. One hundred and forty-four spontaneous miscarriages (27%, 144/534) failed to grow in culture. A total of 27 cases were analysed by QF-PCR for chromosomes 13, 18, 21, X and Y, being informative in all cases.

Conclusion

In our German retrospective large study of spontaneous miscarriages, the incidence and types of chromosome aberrations by CA are within the reported range of other studies published previously before and after 2000. Therefore, we can conclude that cytogenetic aspects of spontaneous miscarriages have not changed over the years. Additionally 8 of 27 cases (30%) without cell growth showed a numerical chromosome aberration by QF-PCR. Therefore QF-PCR played an important role as a supplementary test when culture failure occurred.