The Fetus


Growth and Development


Fetus weighs 1kg at 26-28 weeks, 2.5kg at 36 weeks and about 3.3kg at term.


Lung maturity


Fetal lung maturity is indicated by measuring surface-active lipid components of surfactant (Lecithin and phosphatidylglycerol) in amniotic fluid.




*Surface active phospholipoprotein complex synthesized in type II pneumocytes of mature lungs.


*It decreases surface tension ……..facilitates lung expansion and prevents atelectasis


*In preterm there is insufficient surfactant……progressive atelectasis and RDS.


The most active and abundant lipid components of surfactant are:





*Between 20-22 weeks there is less active palmitoylmyristol Lecithin which can prevent RDS, but it is easily affected by stress and acidosis, that is why preterm usually develop RDS.


*Between 34-36 weeks dipalmitoyl lecithin develop which is more active and prevent RDS.


*L/S ratio

Sphyngomyline present in the amniotic fluid with a ratio of 1:1 with Lecithin until after 34 weeks when L/S ratio become 2 indicating lung maturity.

Also presence of phosphatidyglycerol in the amniotic fluid is indicative of lung maturity even if L/S ratio is not 2.


*stimulation of surfactant is principally by fetal cortisol with synergistic effect of:

-Thyroxin  -prolactin –estrogen –prostaglandin –growth factor


*Stressful conditions with pregnancy enhance synthesis of surfactant:

-hypertensive disorders  -hemoglopinopathies  -heroin addiction  -poor maternal condition  -advanced DM  -IUGR


*Insulin antagonizes the effect of cortisol on lung so lung surfactant with lung immaturity is common with DM(not complicated) and also in Rh-isoimmunization.



*Clinically glucocorticoids are given between 28-34 in cases of threatened preterm labor to enhance lung maturity..

 48-hours are needed for the effect of glucocorticoids to appear which last for 7 days, i.e to be repeated after 1 week.


*The effect is of value between 28-32 weeks, with some benefit between 32-34 weeks and no benefit after 34 weeks.




see fetal physiology

see fetal monitoring



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