amniotic fluid
TRANSCRIPT
Volume• About 500 ml enter and
leave the amniotic sac each
hour.
• Gradual up to 36 wks to
around 600-1000 ml then
after that.
• Normal range is wide but
approx. volumes are:
50 ml 12 wks
400 ml 20 wks
800 ml 34 wks
1000 ml 36-38 wks
At full term, there is
between 600-800 cc of AF
Circulation and Constituents
• Origin: Maternal + Foetal
a) Simple transudation from maternal
blood into placental sinuses
b) Active secretion by chorion and
amnion
c) Foetal urine at full term
d) Foetal skin solid particles (vernix
caseosa) + cellular component
e) Excretions from respiratory tract
f) Alimentary canal: by swallowing
and absorption (as early as 20
wks)
Composition
Composition + volume changes as pregnancy advances
In the 1st ½ of pregnancy, fluid is same as ECF of foetus, devoid of particulate mattero Produced by amniotic membranes
o Fluid also passes across foetal skin
By the 4th month, the foetus contributes to AF via:o urinating
o swallowing
o movement of fluid in and out of the respiratory tract
o Foetal urination will eventually comprise the majority of AF
Foetal kidneys start to develop during 4th and 5th wks of gestation and begin
to excrete urine into AF at the 11th-13th wk
At the 20th wk fetal kidneys produce most of AF
Foetal urine is hypotonic (c/w plasma) because of lower electrolyte
concentration
Contains more urea, creatinine and uric acid
Osmolality with gestational age
• An important function of foetal kidney maintain a urine output sufficient to
maintain AF volume
• Daily urine production is approx. 30% of foetal weight
• The excreted urine does not serve real excretory or homeostatic function
because the urine, via the AF, is recycled back to the foetus by swallowing
(25% of foetal weight)
Function
Allows movement of developing foetus in womb allow
proper bone growth
Proper development of lungs
Maintaining relative constant temp. around baby + protection
from heat loss
Act as cushion protect baby from outside injury or trauma
SDVP
Measurement of deepest, cord-free, devoid of foetal parts,
vertical pocket
Normal range: 2–8 cm
AFI
• Volume of AF is evaluated by visually dividing the
mother's abdomen into 4 quadrants
• The largest vertical pocket of fluid in each
quadrant is measured in cm
• Cord containing pocket < 30%
• Total volume is calculated by adding these values
• < 5 oligohydramnios
o AFI < 5.0 cm had a sensitivity of 18% for the detection of
oligohydramnios
• 6-8 borderline AFI
• 8-24 normal
• > 24 polyhydramnios