Fetal lung development in surgically induced prolonged gestation

In our previous study we prolonged gestation in rats with daily subcutaneous injections of progesterone starting on gestation day 20 (P20). To determine whether exogenous progesterone affects the growth of post-term fetal lungs, we utilized surgical techniques to prolong gestation by retaining 4 living fetuses 1, 2, or 3 days beyond the date of spontaneous delivery of the rest of the litter. The retained fetuses were harvested by caesarean section on gestation days 21 through 25. In spite of an improved general appearance in the retained fetuses, there were many similarities between the retained and the post-term P20 fetuses such as: increase in fetal body, kidney and spleen weights; reduction in lung and liver weights; progressive lung atelectasis; loss of lung and liver glycogen; hypoglycemia; and reduction in placenta DNA content. The significant differences between the two were in the amount of lung disaturated phosphatidyl choline (DSPC) and lung DNA (cell number), expressed per lung or per body weight. In contrast to the P20 post-term fetuses, which exhibited a biphasic phenomenon in DSPC and DNA contents, the retained fetuses showed no change in lung DSPC and DNA contents after term. The P20 fetuses had larger adrenals, which increased with prolongation of gestation. The results suggest that exogenous progesterone does not affect the fetal lung growth post-term. It is speculated that the cellularity and the DSPC content of the post-term fetal lung is adversely affected by the degree of fetal distress.