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Genetic findings associated with molar changes in the placenta
ОглавлениеOne of the most distinct placental phenotypes is that associated with a hydatidiform mole. Complete hydatidiform mole (CHM), PHM, and placental mesenchymal dysplasia (PMD) are related conditions that usually result from genomic imbalance involving an excess of paternal/maternal genomes (Table 4.1). Pregnancy prognosis and management differ depending on diagnosis, as does recurrence risk. Importantly, PMD can be associated with a range of pregnancy outcomes, ranging from miscarriage/intrauterine death to healthy term birth.
Table 4.1 Genomic and chromosomal defects affecting placental function and fetal growth.
| Defect | Mechanism | Placenta/fetus |
|---|---|---|
| Digynic triploidy | Majority the result of errors in maternal second meiotic division (MII) | Very small placenta; no cystic change. Lacy trophoblastic with irregular villus contours. Asymmetric intrauterine growth restriction (IUGR) with associated adrenal hypoplasia. Fetal anomalies attributable to triploidy |
| Diandric triploidy | Fertilization of normal egg by two sperm (dispermy) | Large placenta with cystic villi. Cystic chorionic villi, focal trophoblastic hyperplasia – findings of partial hydatidiform mole. Fetal vasculature present, p57 staining positive (normal). May have symmetric IUGR. Fetal anomalies attributable to triploidy |
| Complete hydatidiform mole (CHM) | Fertilization of egg by two sperm with no contribution from the maternal pronucleus | Grossly evident cystic villi. Cystic chorionic villi, diffuse circumferential trophoblastic hyperplasia, ± cytologic atypia, stromal karyorrhexis. p57 staining negative (abnormal) |
| Androgenetic chimerism/mosaicism | Two cell populations: one normal, one androgenetic (paternal genome only) | Grossly, large placenta, large fetal vessels and associated Wharton's jelly extending into placental disc. Abnormal vessels extend into enlarged and myxomatous appearing stem villi. No trophoblastic hyperplasia. Beckwith–Wiedemann syndrome. Skin and hepatic hemangiomas. Hepatic mesenchymal hamartomas |
| Trisomy 13 | Generally maternal meiotic error | Small placental volume. Reduced fetal growth. Abnormal fetus. Increased risk of maternal preeclampsia |
| Trisomy 18 | Generally maternal meiotic error | Small placenta leading to reduced fetal growth. Fetal anomalies |
| Trisomy 21 | Generally maternal meiotic error | Normal size. Placenta shows deficiencies in the process of cytotrophoblast fusion leading to syncytiotrophoblast formation. Decreased risk of maternal preeclampsia |
| Confined placental mosaicism: trisomy 16 | Almost always maternal meiotic error | Cystic changes on ultrasound. Usually not grossly or histologically cystic. May show irregularities of trophoblast epithelium. Fetal growth restriction is common. Fetal anomalies may occur in a subset of cases |
