How Labor Begins
I came across this fascinating article explains the process in which babies will initiate labor and it all comes down to lung development. "The initiation of term labor is carefully timed to begin only after the embryo is sufficiently mature to survive outside the womb. Previous studies suggested that the signal for labor in humans may arise from the fetus, but the nature of the signal and actual mechanism was unclear. In this study, researchers found that the key labor triggering substance, surfactant, is essential for normal breathing outside the womb. "We found that a protein within lung, surfactant, serves as a hormone of labor that signals to the mother's uterus when the fetal lungs are sufficiently mature to withstand the critical transition from life in fluid to airbreathing," said Mendelson. It also gets into why some mothers might carrier baby past 42 weeks. "Researchers also found that injecting a pregnant mouse with SP-A before day 17 of the pregnancy caused the mouse to deliver early. Injection of pregnant mice with an antibody that blocks SP-A function caused them to deliver late. This would cause us to believe that women who carry babies post 42 weeks (as is common in some family lines) may do so because the necessary SP-A function is happening at later date in gestation (starting at 34 weeks instead of 32 weeks, for example)." So there you have it...babies know when they are ready to be born! For more information or to read the article click here.