Theories of Labor Onset

Theories of Labor Onset Labor is a coordinated sequence of involuntary, intermittent uterine contractions. It is the series ser ies of events that expels expels the fetus fetus and placent placentaa out of the mother’ mother’ss body body.. Thi Thiss is made  possible by the presence of uterine contractions and abdominal pressure that push the fetus out duri du ring ng th thee exp expul ulsi sion on pe peri riod od of de deli liver very. y. Re Regul gular ar co cont ntra ract ctio ions ns re resu sult lt to gr gradu adual al ce cerv rvic ical al effacement and dilatation. Adequate pressure from abdominal muscles allows the baby to be  pushed outside the mother’s womb. Labor and delivery require a woman to utilize her coping methods psychologically and  physiologically. Normally, labor begins when the fetus reaches a mature age (38-42 weeks age of  gestation). This is to ensure survival of the fetus with the extrauterine life. The mechanism that converts Braxton Hicks Contractions (painless contractions) to strong and coordinated uterine contractions is unknown. In some cases, labor occurs before the fetus reaches the mature age (preterm birth) while in others it is delayed (postterm birth). Although Altho ugh the exact mechanism mechanism that initiates initiates labor is unknown. Theories Theories have been proposed to explain how and why labor occurs. Uterine Stretch theory The idea is based on the concept that any hollow body organ when stretched to its capacity will inevitably contract to expel its contents. The uterus, which is a hollow muscular organ,  becomes stretched due to the growing fetal structures. In return, the pressure increases causing  physiologic changes (uterine contractions) that initiate labor. Oxytocin theory Pressu Pre ssure re on the cer cervix vix sti stimul mulate atess the hypo hypophys physis is to rel releas easee oxyt oxytoci ocin n fro from m the mat matern ernal al  posterior pituitary gland. As pregnancy advances, the uterus becomes more sensitive to oxytocin. Presence of this hormone causes the initiation of contraction of the smooth muscles of the  body(uterus is composed of smooth muscles). Progesterone deprivation theory Progesterone is the hormone designed to promote pregnancy. It is believed that presence of  this hormone inhibits uterine motility. As pregnancy advances, changes in the relative effects estrogen and progesterone encourage the onset of labor. A marked increase in estrogen level is noted not ed in rel relati ation on to pro proges gester terone one,, mak making ing the lat latter ter hor hormon monee les lesss eff effect ective ive in cont control rollin ling g rhythm rhy thmic ic ute uterin rinee cont contrac racti tions ons.. Al Also, so, in lat later er pre pregnan gnancy, cy, ris rising ing fet fetal al cor cortis tisol ol lev levels els inh inhibi ibitt  progesterone production from the placenta. Reduce progesterone formation initiates labor. Prostaglandin theory In the latter part of pregnancy, fetal membranes and uterine decidua increase prostaglandin levels. This hormone is secreted from the lower area of the fetal membrane (forebag). A decrease in progesterone amount also elevates the prostaglandin level. Synthesis of prostaglandin, in return, causes uterine contraction thus, labor is initiated. Theory of Aging Placenta Advance Adva nce pla placent cental al age dec decrea reases ses blo blood od sup supply ply to the ute uterus rus.. Thi Thiss eve event nt tri trigger ggerss ute uterin rinee contractions, thereby, starting the labor 

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