Abnormalities of Placenta

Abnormalities of the Placenta

The placenta develops from  the chorion frondosum (foetal origin) and decidua basalis  (maternal origin).

Anatomy At Term

• Shape     :  discoid.
• Diameter : 15-20 cm.
• Weight : 500 gm.
• Thickness: 2.5 cm at its center and gradually tapers towards the periphery.
• Position : in the upper uterine segment (99.5%), either in the posterior surface (2/3) or the anterior surface (1/3).

Surfaces

• Foetal surface
• Maternal surface

Foetal surface

• Smooth, glistening and is covered by the amnion which is reflected on the cord.
• The umbilical cord is inserted near or at the center of this surface and its radiating branches can be seen beneath the amnion.

Maternal surface

• Dull greyish red in colour and is divided into 15-20 cotyledons.
• Each cotyledon is formed of the branches of one main villus stem covered by decidua basalis

 

Abnormalities of the Placenta

(A) Abnormal Shape:

1. Placenta Bipartite
2. Placenta Succenturiata
3. Placenta Circumvallata
4. Placenta Fenestrata

 The placenta consists of two equal lobes connected by placental tissue

 

1. Placenta Bipartite:

• The placenta consists of two equal parts connected by membranes.
• The umbilical cord is inserted in one lobe and branches from its vessels cross the membranes to the other lobe.
• Rarely, the umbilical cord divides into two branches, each supplies a lobe.
• The placenta consists of a large lobe and a smaller one connecting together by membranes.
• The umbilical cord is inserted into the large lobe and branches of its vessels cross the membranes to the small succenturiate (accessory) lobe.

 2. Placenta Succenturiata:

• The accessory lobe may be retained in the uterus after delivery leading to postpartum haemorrhage.
• This is suspected if a circular gap is detected in the membranes from which blood vessels pass towards the edge of the main placenta.
• A whitish ring composed of decidua, is seen around the placenta from its foetal surface.
• This may result when the chorion frondosum is two small for the nutrition of the foetus, so the peripheral villi grow in such a way splitting the decidua basalis into a superficial layer ( the whitish ring) and a deep layer.

 3. Placenta Circumvallata:

• It can be a cause of :
• Abortion,
• Ante partum haemorrhage,
• Preterm labour        and
• Intrauterine foetal death.

4.  Placenta Fenestrata:

• A gap is seen in the placenta covered by membranes giving the appearance of a window.

 5. Placenta membranacea:

• A great part of the chorion develops into placental tissue.
• The placenta is large, thin and may measure 30-40 cm in diameter.
• It may encroach on the lower uterine segment i.e. placenta praevia.

 (B) Abnormal Weight:

The placenta increases in size and weight as in :

• Congenital syphilis,
• Hydrops foetalis
• Diabetes mellitus.

Placenta Praevia

The placenta is partly or completely attached to the lower uterine segment

In this gravid uterus, the placenta implanted over the os. This is called placenta previa.
Implantation in this low lying position can lead to extensive hemorrhage as the dilation of the cervix disrupts the placenta.

(C) Abnormal Adhesion:

• Placenta Accreta:The chorionic villi penetrate deeply into the uterine wall to reach the myometrium,due to deficient decidua basalis.
• Placenta increta:When the villi penetrate deeply into the myometrium, it is called "placenta increta" 

• Placenta percreta: When they reach the peritoneal coat it is called "placenta percreta".

(D) Placental Lesions

Seen in placenta at term, mainly in hypertensive states with pregnancy.

• White infracts: due to excessive fibrin deposition. (Normal placenta may contain white infracts in which calcium deposition may occur).
• Red infarcts : due to haemorrhage from the maternal vessels of the decidua. (Old red infarcts finally become white due to fibrin deposition).

(E) Placental Tumour:

• Chorioangioma : is a rare benign tumour of the placental blood vessels which may be associated with hydramnios.