Amniotic Fluid

Phosphtidyl glycerol estimation in amniotic fluid REF: Williams Obstetrics 22nd ed Chapter 29

Several procedures have been proposed for its evaluation but two of them (L/S ratio, “shake test” and phosphatidylglycerol in amniotic fluid) have been widely acclaimed.

According to Williams estimation of phosphatidylcholine or phosphatidylglycerol is better and more sensitive and specific for lung maturity because phosphatidylglycerol is not detected in blood, meconium, or vaginal secretions; these contaminants do not confuse its interpretation

The same view is supported by nelson.

Skin maturity test [Ref. Dutta 6¹¹⁷/e p 317, Meherban Singh care of newborn 6^th/e p 43; Indian journal of pediatrics volume 51. number 2 159-163 do 1101007 K. L srivastava, P.K. mishra, P. mehra. R lau1J

• According to Dutta, Nile blue sulphatase test is done for confirming rupture of membranes

“Centrifuged cells stained with .1% Nile blue sulphate shows orange blue colouration of the cells (exfoliated fat containing cells from sebaceous gland of the fetus)”

According to Meherban Singh

• Nile blue sulphatase test detects the presence of lipid containing epithelial cells from subaceous glands of fetal
  skin. The sebaceous gland of the fetus produce cells containing lipid so stained orange with nile blue sulphatase.
• These cells are shed in the amniotic fluid.
• When these cells are stained with nile blue sulphatase, they give orange staining.
• When proportion of orange staining cells is > 20%, it is indicative of full fetal maturity.

According to Indian Journal of pediatrics

• “The origin of lipid containing cells in the amniotic fluid as detected by Nile Blue sulphate has been reported to
  be fairly usefid and easy test for assessment of fetal skin maturity and thereby indirectly of gestational age”.

According to International Journal of obstetrics and Gynaecology

• .”The sebaceous glands of the fetus produce cells containing lipid which are stained orange with Nile blue sulphate.

If 50% or more of the cells in the amniotic fluid are of these types, the foetus is mature”.

Open spina bifida [Ref. Clinical diagnosis and management by Henry 20^th/e p 451, 452]

Role of acetylcholinesterase in amniotic fluid assessment

• If a patient is suspected of neural tube defect, besides alpha fetoprotein, acetylcholinesterase is also used.
• Acetykholinesterase is an enzyme specifically derived from neural tissues.
• It is neural tissue specific and has very high concentration in cerebrospinal fluid.
• Therefore it can be used as sensitive and specific marker for open neural tube defects.
• Laboratories that analyze amniotic fluid AFP levels should examine acetylcholiinesterase in any sample that has elevated AFP levels (> 2^.0 MoM), since AchE can help to identify open neural tube defects that might not be visible by ultrasound, discriminate NTD’s from other fetal defects with increased AFP and rule out false positive AFP results.

Amniotic fluid measures about 50 ml at 12 weeks, 400 ml at 20 weeks and reaches its peak of 1 litre at 36-38 weeks.

Thereafter the amount diminishes, till at term it measures about 600-800 ml.

This fluid is faintly alkaline with low specific gravity of 1.010 An osmolarity of 250 mOsmol/litre is suggestive of fetal maturity.

• Meconium stained green colour is suggestive of fetal distress.
• Golden colour in Rh incompatibility is due to excessive haemolysis of fetal RBC and production of excess bilirubin.
• Greenish yellow (saffron)seen in post maturity
• Dark coloured in concealed accidental haemorrhage is due to contamination.
• Dark brown amniotic fluid is found in I.U.D. The dark colour is due to frequent presence of old HbA.

Amniocentesis is done during 16th week of pregnancy.

Fetal blood sampling is done after 17-18 weeks, chorionic villi during 11-12 weeks of pregnancy, maternal blood AFP during 15-20 weeks.

Ref:  Textbook of Gynaecology By Dutta, 6th Edition, Page 108; In-Vitro Fertilization By Kay Elder, Brian Dale, Yves Ménézo, Joyce Harper, John Huntriss, 2010, Page 243; Donald School Textbook of Ultrasound in Obstetrics and Gynecology By Asim Kurjak, 2008, Page 755.

Amniotic fluid measures about 50 ml at 12 weeks, 400 ml at 20 weeks and reaches its peak of 1 litre at 36-38 weeks.

Thereafter the amount diminishes, till at term it measures about 600-800 ml. As the pregnancy continues post term, further reduction occurs to the extent of about 200 ml at 43 weeks.

800 cc

7.0 – 7.5

7.2

Rh incompatibility

3 hours

Fetal urine

Intrauterine death

Ans. is b i.e. Fetus

“The precise origin of the amniotic fluid remains unsolved and amniotic fluid is considered to be both of maternal and fetal origin.”

But this cannot help us to solve this question.

Let’s see what Williams Obs. has to say on Origin of Amniotic fluid.

‘-in early pregnancy, amniotic hula is an ultranmate or materna’ plasma. By the beginning of second trimester, it consists largely of extracellular fluid which diffuses through the fetal skin, and thus reflects the composition of fetal plasma.

After 20 weeks, however, the cornification of fetal skin prevents this diffusion and amniotic fluid is composed largely of fetal urine.”

Reading the above text, it can be concluded that in early pregnancy – Mother is the main contributor whereas during rest of the pregnancy – Fetus is the main contributor.

Ans. is b i.e. 32 weeks

Friends, I had to search a lot for this answer but all in vain.

Only Nelson Paediatric throws some light on this issue :

“Pulmonary surfactant is a heterogenous mixture of phospholipids and proteins secreted into the sac­cular or alveolar sub-phase by the type ll pneumocytes. Its presence is first recognised in characteristic secretory organelles known as lamellar bodies as early as the 24th week of gestation. However, surfac­tant lipids of which the most abundant is phosphatidyicholine, are not detectable in the amniotic fluid until the 30th week of gestation, suggesting that there is a chronologic gap between surfactant synthesis and secretion. Labour probably shortens this gap because phospholipids are consistently found in the air spaces of infants born before the 30th week of gestation.”

From the above lines it is clear :

Surfactant synthesis occurs in 24th week of gestation, it appear in amniotic fluid in 30th week of gestation. Since 30 weeks is not given in options, I would personally go with 32 weeks, when surfactant will absolutely be detected in amniotic fluid, whereas at 28 weeks it can detected only if preterm labour occurs.

Ans. is a, b, c 

Amniotic fluid originates from

• In early pregnancy – As an ultrafiltrate of maternal plasma (i.e., option “b” correct).
• By beginning of the second trimester – It consists of extracellular fluid which diffuses through the fetal skin (i.e., option “e”).
• After 20 weeks – Cornification of skin prevents this diffusion and amniotic fluid is composed of fetal urine (option “a” correct).

Also know : The water in the amniotic fluid is completely changed and replaced in every 3 hours.

Other minor contributors : • Pulmonary fluid

• Fluid filtering through the placenta

The fetus swallows 200 – 500 ml liquor every day at term. (Option “c” correct) i.e. Excretion by fetal kidneys; Maternal hemostasis; Fetal intestinal absorption

Peripheral lymphocytes

Ans. Amniotic fluid embolism