BGDA Practical Placenta - Abnormalities
- 1 Hydatidiform Mole
- 2 Implantation Abnormalities
- 3 Cord Abnormalities
- 4 Additional Information
- 5 Glossary Links
Another type of abnormality is when only the conceptus trophoblast layers proliferates and not the embryoblast, no embryo develops, this is called a "hydatidiform mole" (HM), which is due to the continuing presence of the trophoblastic layer, this abnormal conceptus can also implant in the uterus. The trophoblast cells will secrete human chorionic gonadotropin (hCG), as in a normal pregnancy, and may appear maternally and by pregnancy test to be "normal". Prenatal diagnosis by ultrasound analysis demonstrates the absence of a embryo.
There are several forms of hydatidiform mole: partial mole, complete mole and persistent gestational trophoblastic tumor.
- Complete Mole - Only paternal chromosomes, chromosomal genetic material from the ovum (egg) is lost, by an unknown process.
- Partial Mole - Ultrasound of partial mole confirmed by triploidy, chromosomal (genetic) material from the ovum (egg) is retained and the egg is fertilized by one or two sperm.
On ultrasound the tumour has a "grape-like" placental appearance without enclosed embryo formation. Following a first molar pregnancy, there is approximately a 1% risk of a second molar pregnancy.
- The incidence of hydatidiform mole varies between ethnic groups, and typically occurs in 1 in every 1500 pregnancies.
- All hydatidiform mole cases are sporadic, except for extremely rare familial cases.
Placenta previa and increta
The placenta is a mateno-fetal organ which begins developing at implantation of the blastocyst and is delivered with the fetus at birth. As the fetus relies on the placenta for not only nutrition, but many other developmentally essential functions, the correct development of the placenta is important to correct embryonic and fetal development.
Abnormalities can range from anatomical associated with degree or site of inplantation, structure (as with twinning), to placental function, placento-maternal effects (pre-eclampsia, fetal erythroblastosis) and finally mechanical abnormalities associated with the placental (umbilical) cord.
- Placenta Accreta - abnormal adherence, with absence of decidua basalis. The incidence of placenta accreta also significantly increases in women with previous cesarean section compared to those without a prior surgical delivery.
- Placenta Increta - occurs when the placenta attaches deep into the uterine wall and penetrates into the uterine muscle, but does not penetrate the uterine serosa. Placenta increta accounts for approximately 15-17% of all cases.
- Placenta Percreta - placental villi penetrate myometrium and through to uterine serosa.
- Placenta Previa - In this placenatal abnormality, the placenta overlies internal os of uterus, essentially covering the birth canal. This condition occurs in approximately 1 in 200 to 250 pregnancies. In the third trimester and at term, abnormal bleeding can require cesarian delivery and can also lead to Abruptio Placenta. Ultrasound screening programs during 1st and early 2nd trimester pregnancies now include placental localization. Diagnosis can also be made by transvaginal ultrasound.
- Vasa Previa - (vasa praevia) placental abnormality where the fetal vessels lie within the membranes close too or crossing the inner cervical os (opening). Two main associations; 1. velamentous insertions (25–62%) and 2. vessels crossing between lobes in succenturiate or bilobate placentas (33–75%)
- Multilobed Placenta Succenturiata - an accessory portion attached to the main placenta by an artery or vein.
- Abruptio Placenta - a retroplacental blood clot formation, abnormal haemorrhage prior to delivery.
- Chronic Intervillositis - (massive chronicintervillositis, chronic histiocytic intervillositis) Rare placental abnormality and pathology defined by inflammatory placental lesions, mainly in the intervillous space (IVS), with a maternal infiltrate of mononuclear cells (monocytes, lymphocytes, histiocytes) and intervillous fibrinoid deposition.
Velamentous Cord Insertion of the Placenta
The placental cord inserts into the chorion laeve (placental membranes) away from the edge of the placenta.
The placental vessels are therefore unprotected by Wharton's jelly where they traverse the membranes before they come together into the umbilical cord.
This can also be associated with vasa previa (see above) or haemorrhage caused if the vessels are damaged when the membranes are ruptured prior to birth. The condition is more common in monozygotic twins (15%) and triplets.
Excessively short or long cords (see additional information on cord page). Abnormally long cords may wrap around either extremities or neck of the fetus.
Cord Vessel Number
Cord with only one artery and one vein.
Cord knotting can occur (1%) in most cases these knots have no effect, in some cases of severe knotting this can prevents the passage of placental blood.
Umbilical cord torsion
Rare umbilical cord torsion, even without knot formation can also affect placental blood flow, even leading to fetal demise.
Practical 14: Implantation and Early Placentation | Villi Development | Maternal Decidua | Cord Development | Placental Functions | Diagnostic Techniques | Abnormalities
- Content shown under this heading is not part of the material covered in this class. It is provided for those students who would like to know about some concepts or current research in topics related to the current class page.
Royal Hospital for Women
- "A one-minute examination of the placenta performed in the delivery room provides information that may be important to the care of both mother and infant. The findings of this assessment should be documented in the delivery records. During the examination, the size, shape, consistency and completeness of the placenta should be determined, and the presence of accessory lobes, placental infarcts, hemorrhage, tumors and nodules should be noted. The umbilical cord should be assessed for length, insertion, number of vessels, thromboses, knots and the presence of Wharton's jelly. The color, luster and odor of the fetal membranes should be evaluated, and the membranes should be examined for the presence of large (velamentous) vessels. Tissue may be retained because of abnormal lobation of the placenta or because of placenta accreta, placenta increta or placenta percreta. Numerous common and uncommon findings of the placenta, umbilical cord and membranes are associated with abnormal fetal development and perinatal morbidity. The placenta should be submitted for pathologic evaluation if an abnormality is detected or certain indications are present."
- This condition is also known as gestational proteinuric hypertension and occurs in occurs in approximately 2 to 4% of all pregnancies. The pathogenesis of eclamptic convulsions remains unknown and women with a history of eclampsia are at increased risk of eclampsia (1-2%) and preeclampsia (22-35%) in subsequent pregnancies.
- A large population study in Norway has shown a strong generational association such that daughters of women who had pre-eclampsia during pregnancy had more than twice the risk of pre-eclampsia themselves. The paper concludes "Maternal genes and fetal genes from either the mother or father may trigger pre-eclampsia. The maternal association is stronger than the fetal association. The familial association predicts more severe pre-eclampsia."
Rolv Skjaerven, Lars J Vatten, Allen J Wilcox, Thorbjørn Rønning, Lorentz M Irgens, Rolv Terje Lie Recurrence of pre-eclampsia across generations: exploring fetal and maternal genetic components in a population based cohort. BMJ: 2005, 331(7521);877 PMID: 16169871
|Monochorionic twin pregnancies||Monochorionic triamniotic triplet pregnancy placenta|
Other Online Resources
- Placenta Links: Introduction | Lecture - Placenta | Practical - Placenta | Implantation | Villi Development | Trophoblast | Maternal Decidua | Endocrine | Cord | Membranes | Abnormalities | Stage 13 | Stage 22 | Histology | Vascular Beds | Blood Vessel Development | Stem Cells | Category:Placenta
- Juliana Rocha, Joana Carvalho, Fernanda Costa, Isabel Meireles, Olímpia do Carmo Velamentous cord insertion in a singleton pregnancy: an obscure cause of emergency cesarean-a case report. Case Rep Obstet Gynecol: 2012, 2012;308206 PMID: 23243528 | PMC3517836 | Case Rep Obstet Gynecol.
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Cite this page: Hill, M.A. (2015) Embryology BGDA Practical Placenta - Abnormalities. Retrieved June 2, 2015, from https://embryology.med.unsw.edu.au/embryology/index.php/BGDA_Practical_Placenta_-_Abnormalities
- © Dr Mark Hill 2015, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G