The Fetal membranes consist of two layers – outer chorion and the inner amnion.
◾Chorion : It ends at the margin of the placenta. It in thicker than amnion, friable(easily crumble) and shaggy(long, thick and untidy) on both the sides. ✔️Internally, it is attached to the amnion by loose areolar tissue
and remnant of primitive mesenchyme. ✔️Externally, it is covered by vestiges of trophoblastic layer and the
decidual cells of the fused decidua capsularis and parietalis.
♦️Therefore, human placenta is a discoid(shape), deciduate(endometrium of pregnant women), labyrinthine(complicated irregular network of passages) and hemochorial(fetal epithelium bathed in maternal blood) type.
◾Amnion : It is the inner layer of the fetal membranes. Its internal surface is smooth and shiny and is in contact
with liquor amnii.
✔️ The outer surface consists of a layer
of connective tissue and is apposed(side by side) to the similar tissue on the inner aspect of the chorion from which it can be
peeled off. The amnion can also be peeled off from the fetal surface of the placenta except at the insertion of the umbilical cord.
◾Function:
- Contribute to the formation of liquor amnii
- Intact membranes prevent ascending uterine infection
- Facilitate dilatation of the cervix during labour.
- Has got enzymatic activities for steroid hormonal metabolism.
- Rich source of glycerophospholipids containing arachidonic acid-precursor of prostaglandin
Amniotic Fluid
◾Volume- Its volume is related to gestational age. It measures about
- 50 ml at 12 weeks
- 400 ml at 20 weeks
- 1 litre at 36- 38 weeks (peak)
- Thereafter volume diminishes
◾Physical features- It is faintly alkaline, specific gravity(low) – 1.010
Colour- In early pregnancy, colourless but near term it becomes pale straw coloured.
Abnormal colour-
- Meconium stained(green) is due to fetal distress in presentations other than breech and transverse.
- Golden colour in Rh incompatibility
- Greenish yellow in post maturity
- Dark coloured in accidental Haemorrhage
- Dark brown found in IUD.
◾Composition- It includes water (98-99%) and solid(1-2%).
- Organic- protein, glucose, urea, uric acid, creatinine, hormones
- Inorganic- sodium, chloride and potassium
- Suspended particles- lanugo, exfoliated squamous epithelial cells, vernix caseosa and cells from other organs of fetus.
◾Function- major function is to protect the fetus.
- During pregnancy, it act as shock absorber, maintain temperature, supply adequate water to fetus.
- During labour, the chorion and amnion combine to help in Dilatation of cervix, and has aseptic and bactericidal action to protect fetus from infection.
◾Clinical importance-
- It’s study provide information about well and maturity of fetus.
- Volume of liquor amnii is assessed by amniotic fluid index(AFI). It is measured to diagnose the Clinical condition of polyhydramnios or oligohydramnios.
- During induction of labour, rupture of membranes and drainage of liquor is helpful.