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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.

 

Surfactant

 

*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:

1-phosphatidylcholine(Lecithin)

2-phosphatidylglycerol

 

 

*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.

 

 

Google

see fetal physiology

see fetal monitoring

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