Digynic triploidy: utility and challenges of noninvasive prenatal testing

[Twin gestation with regressive partial hydatidiform mole and coexisting live fetus]

The case of dichorionic twin pregnancy is described, with a fused placenta, one part of which is represented by a tissue of partial hydatidiform mole (PHM) with signs of regression, the second part is a placenta of a common structure with a normal development of the second twin. The delivery took place at the term of 38 weeks with a live healthy girl weighing 3250 g. A single placental disc consisted of two fused placentas with a clear boundary between them. The placenta of a live-born girl was mature, with focal chorangiosis, the second part of the disc was represented by the PHM tissue with avascular giant bizarre villi, some of them with central cisterns, with stromal fibrosis, low proliferative activity of the villous trophoblast and a significant narrowing of the intervillous space. A genetic study was carried out on the material of paraffin blocks from two parts of the placental disc containing the tissue of the villous chorion, and the blood of the parents. Comparative analysis of DNA isolated from the paraffin block of PHM with the DNA of the parents revealed the presence of diandric dispermic triploidy. No chromosomal pathology was found in the placenta of a living girl. For hydatidiform mole in the case of multiple pregnancy, an increase in the volume of the affected placenta is characteristic compared to the normal placenta of the twin. In our observation, the presence in the placenta with PHM signs characteristic of placentas with antenatal fetal death, stromal fibrosis of the villi and low proliferative activity of the trophoblast suggests a regression of PHM.

Cell-free fetal DNA coming in all sizes and shapes

Cell‐free fetal DNA analysis has an established role in prenatal assessments. It serves as a source of fetal genetic material that is accessible non‐invasively from maternal blood. Through the years, evidence has accumulated to show that cell‐free fetal DNA molecules are derived from placental tissues, are mainly of short DNA fragments and have rapid post‐delivery clearance profiles. But questions regarding how they come to being short molecules from placental cells and in which physical forms do they exist remained largely unanswered until recently. We now know that the distributions of ending sites of cell‐free DNA molecules are non‐random across the genome and bear correlations with the chromatin structures of cells from which they have originated. Such an insight offers ways to deduce the tissue‐of‐origin of these molecules. Besides, the physical nature and sequence characteristics of the ends of each cell‐free DNA molecule provide tell‐tale signs of how the DNA fragmentation processes are orchestrated by nuclease enzymes. These realizations offered opportunities to develop methods for enriching cell‐free fetal DNA to facilitate non‐invasive prenatal diagnostics. Here we aimed to collate what is known about the biological and physical characteristics of cell‐free fetal DNA into one article and explain the implications of these observations.

What’s already known about this topic?

Cell‐free fetal DNA originates from placental tissues and circulates in maternal plasma as a minor population in the form of short fragments which disappears from maternal circulation rapidly after delivery.

What does this study add?

Cell‐free DNA studies at the per molecule per nucleotide level documented the detailed genomic distributions, fragment end characteristics and physical forms of cell‐free DNA unveiling the fine feature differences between maternal and fetal DNA as well as their intricate relationships with the chromatin structure of the cells‐of‐origin. These studies have substantially bridged the knowledge gaps in the biology of cell‐free fetal DNA and may provide insights on how to enhance prenatal tests based on their analyses.

Patterns of Placental Injury in Congenital Anomalies in Second Half of Pregnancy

BACKGROUND

Placental pathology in fetal congenital anomalies in second half of pregnancy is largely unknown.

METHODS

Twenty-six clinical and 45 independent placental phenotypes from pregnancies ≥20 weeks of gestation with congenital anomalies divided into 4 groups were retrospectively compared with analysis of variance or χ ² with 3 degrees of freedom and with Bonferroni correction for multiple comparisons: group 1 : 112 cases with heart malformations (with or without chromosomal anomalies), group 2 : 41 cases with abnormal karyotypes and anomalies other than heart malformations, group 3 : 87 cases with intrathoracic or intraabdominal mass-forming anomalies (mostly congenital diaphragmatic hernias and adenomatoid airway malformation), and group 4 : 291 miscellaneous cases with mostly skeletal, renal, and central nervous system anomalies not fulfilling the criteria of inclusion into groups 1 to 3.

RESULTS

Eight of 26 clinical (30.8%) and 16 of 45 (35.5%) placental phenotypes varied statistically significantly among the 4 groups (P <  .05), of those, 7 (26.9%) and 4 (8.9%), respectively, remained statistically significant after Bonferroni correction (P Bonferroni ≤  .002). Those placental phenotypes were placental weight, chorionic disc chorionic microcysts, fetal vascular ectasia, and luminal vascular abnormalities of chorionic villi.

CONCLUSIONS

Fetal anomalies in second half of pregnancy feature abnormal clinical phenotypes much more frequently than abnormal placental phenotypes. Chromosomal abnormalities with or without heart malformations tend to feature villous edema, and erythroblastosis of fetal blood, likely due to fetal heart failure. Mass-forming fetal anomalies feature placental histological lesions of shallow placental implantation, diffuse chronic hypoxic patterns of placental injury, and lesions of fetal vascular malperfusion, likely stasis-induced.

Digynic triploidy in a fetus presenting with semilobar holoprosencephaly

OBJECTIVE

We present digynic triploidy in a fetus with semilobar holoprosencephaly (HPE).

CASE REPORT

A 32-year-old, gravid 1, para 0, woman underwent prenatal ultrasound examination at 12 weeks of gestation, and the ultrasound showed relative macrocephaly, a small non-cystic placenta, and a fetus with absent nasal bone and semilobar HPE. The pregnancy was terminated subsequently, and a 50-g fetus was delivered with a relatively enlarged head and premaxillary agenesis. The placenta was small and non-cystic. Postnatal cytogenetic analysis of the umbilical cord revealed a karyotype of 69, XXX. Postnatal DNA marker analysis using quantitative fluorescent polymerase chain reaction assays and the polymorphic short tandem repeat markers for chromosome 18 and 20 on the placental tissues showed a diallelic pattern with a dosage of 1:2 (paternal allele to maternal allele ratio), indicating a maternal origin of the triploidy.

CONCLUSION

Fetuses with digynic triploidy may present relative macrocephaly, semilobar HPE and a small placenta on prenatal ultrasound.