How do findings on the timing of birth illustrate bidirectional influences between mother and fetus?

Answer 1

Upon investigation, researchers have found that another placental hormone, corticotrophin-releasing hormone (CRH) is involved in the production of estrogen and leads it to overwhelm progesterone. For example, women who go into premature labor have higher blood levels of CRH than do other women in the same week of pregnancy. In fact, CRH levels measured as early as the 16th to 20th week are good predictors of whether a woman will give birth early, on time, or past her due date.

When CRH reaches a high enough level, it leads the fetal adrenal glands to produce cortisol, a stress hormone that clears the infants' lungs of fluid so they are ready to breathe air. Cortisol further stimulates CRH production, which triggers estrogen secretion in the placenta, resulting in the rapid estrogen rise required for labor.

Researchers are still trying to determine what causes the placenta to make CRH, and what affects and how much is produced. The genetic makeup of CRH-producing cells may lead CRH to rise too early in some women, resulting in prematurity. Another potential influence is maternal nutrition. Food deprivation precipitates early birth in some mammals, and the same effect may occur in humans. What is known is that a complex hormonal system, initiated by CRH and involving both mother and fetus, controls the timing of birth.