Growth and Development
Fetus weighs 1kg at 26-28 weeks, 2.5kg at 36 weeks and about 3.3kg at term.
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.
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.
see fetal physiology
see fetal monitoring