Before childbirth
What is the signal for the onset of labor is unknown, but there are many factors affecting the start of the cascade of events that result in the birth of the fetus. The level of progesterone, plated by the placenta in the mother's bloodstream, reaches its peak before delivery. Progesterone is the hormone responsible for maintaining a pregnancy. It has a relaxing effect on the smooth musculature of the uterus.
Hormonal signals
Near the end of pregnancy, the intrauterine space gradually decreases, and oxygen delivery to the fetus progressively decreases (the placenta can no longer meet the needs of a rapidly growing fetus). This leads to increased secretion of adrenocorticotropic hormone (ACTH) in the anterior lobe of the fetal pituitary gland. ACTH stimulates the adrenal cortex, which secretes glucocorticoids, which exert a retarding effect on the secretion of progesterone in the placenta. At the same time, the level of estrogen produced by the placenta becomes maximum, which is accompanied by the appearance on the muscle cells of the uterus receptors for oxytocin (the uterus becomes more sensitive to oxytocin).
Skirmishes
Gradually, the inhibitory effect of progesterone on the smooth muscle cells of the uterus is suppressed by the increasing stimulating effect of estrogens. Pregnant begins to feel the first weak irregular uterine contractions, known as Braxton-Hicks contractions. They contribute to the softening of the cervix in preparation for the birth of a child and are often mistaken for a woman as the beginning of childbirth. By the end of pregnancy, the cervical extension receptors activate the mother's hypothalamus (brain area), which stimulates the pituitary to release the hormone oxytocin. This hormone also produces some fetal cells. When the level of oxytocin increases, the placenta begins to synthesize prostaglandins, which also take part in uterine contractions.
Strengthening of contractions
As the uterus becomes more sensitive to oxytocin, contractions gradually increase and increase. Regular strong contractions indicate the onset of labor. As the contractions intensify, the positive feedback mechanism provides an increase in the synthesis of oxytocin, which in turn leads to even more intensive uterine contractions. This mechanism ceases to function after delivery, when the cervix ceases to be stretched. The process of childbirth is divided into three stages: the opening of the cervix, the expulsion of the fetus and the birth of the placenta.
Disclosure
To the head of the child could pass through the birth canal, the cervix and the vagina should stretch to about 10 cm in diameter. Childbirth begins with irregular weak contractions in the upper part of the uterus. These initial reductions last about 10-30 seconds at intervals of 15-30 minutes. As the labor progresses, contractions become more frequent and intense and gradually move to the lower part of the uterus. The head of the fetus presses against the cervix of the uterus at every contraction, which facilitates its softening and gradual opening. At a certain time, the amniotic membrane that protects the fetus during pregnancy, and the outflow of amniotic fluid, breaks down.
Insertion
The disclosure period is the longest stage of labor, lasting from 8 to 24 hours. In this phase, the fetus begins its journey along the generic canal, simultaneously making a turn. Finally, the head is inserted into the mother's small pelvis. The second stage of labor begins from the full disclosure of the cervix until the moment of the actual birth of the child. With full disclosure of the cervix, powerful contractions last about a minute and are repeated every 2-3 minutes.
Attempts
During this period the mother is experiencing an irresistible desire to push with the abdominal muscles. This phase can last up to two hours, with repeated childbirth is usually less.
Childbirth
Erection of the head begins when its largest volume reaches the vagina. Often excessive stretching of the vagina is accompanied by its ruptures. After the appearance of the head, the rest of the baby's body is born without difficulty. At the head presentation of the first through the birth canal passes the largest part of the fetus - the head that widens the cervix. In this case, the child can begin to breathe before full birth. The final stage of labor - the birth of the placenta - takes about 30 minutes. After the birth of the fetus, rhythmic contractions of the uterus continue. Pressure of the uterine blood vessels limits bleeding. Reduction of the uterine walls leads to the separation of the placenta. The placenta and membranes (the latter) are removed from the uterine cavity by gently pulling at the umbilical cord. To avoid prolonged bleeding and infection after delivery, all fragments of the placenta must be removed from the uterus. The absence of the umbilical artery is often associated with cardiovascular anomalies of the fetus, so always check the number of vessels in the umbilical cord.
Levels of hormones
The levels of estrogens and progesterone in the mother's blood drop sharply after the birth of their source - the placenta. Within four to five weeks, the uterus is significantly reduced, but remains somewhat larger in size than before pregnancy. Now we know when the first signs of labor begin.