amniotic fluid

Question 1

How much amniotic fluid is there at birth? where does it originate?

Answer 1

there is 0.5 to 1 liter of amniotic fluid at birth. The fluid comes from:

1. from maternal blood in chorion leave by transport across amniotic membrane
2. across the embryonic/early fetal skin before keratinization
3. fetal respiratory tract
4. fetal urinary system produces and excretes urine which is mostly water since waste is cleared by circulatory system back to the maternal circulation.

Question 2

what is amniotic fluid made of?

Answer 2

1. 99% water
2. fetal epithelial cells which can be examined by amniocentesis and karyotyping
3. protein such as alpha-fetoprotein
4. fatty acids, amino acids, etc.

Question 3

what can high alpha-fetoprotein in amniotic fluid indicate? low level?

Answer 3

high, neural tube defect.

low, chromosome abnormalities like Trisomy 21 (Down Syndrome)

Question 4

How often is amniotic fluid replaced? How?

Answer 4

every three hours.
It is resorbed through the amniotic membrane back to the maternal circulation and by fetal swallowing of amniotic fluid (approx. 400 cc/day) this fluid is absorbed through fetal gut and goes back to maternal circulation as well.

Question 5

what happens to chorionic cavity as amnion grows?

Answer 5

amnion expansion eliminates the chorionic cavity and the amniotic and chorionic membranes may fuse.

Question 6

How do the chorionic and amniotic membranes differ?

Answer 6

the chorionic membrane is thicker and not as clear. The amniotic membrane, because of its requirement for fluid exchange, is thinner and therefore more transparent.

Question 7

possible abnormal developments of amnion or its fluid?

Answer 7

1. less than normal amounts
   2 too much
2. amniotic band syndrome

Question 8

oligohydramnios. what is it? what causes it?

Answer 8

less than normal amounts of amniotic fluid (approx 400 cc). may be caused by a failure in fetal kidney development (renal agenesis) and/or obstruction in the urinary system (obstructive uropathy) resulting in no fetal contribution to the amniotic fluid.

Question 9

what complications can happen with oligohydramnios?

Answer 9

malformations due to insufficient room for development of the thorax and limbs as well as decreased potential for movement.

Question 10

what is polyhydramnios? what does it indicate? what are possible malformations?

Answer 10

too much amniotic fluid (1500-2000 cc). indicates malformations affecting the ability of the fetus to swallow amniotic fluid. possible malformations include anencephaly and/or esophageal atresia.

Question 11

what is amniotic band syndrome?

Answer 11

a strip of amniotic membrane can become detached and wrap around a fetal structure. the structure can become constricted and can event be cut off by tightening of the amniotic band. occurs in about 1:1200 live births.