The physiology of childbirth
Childbirth is a natural process in which cervical dilatation, the birth of the baby and the placenta from the mother’s uterus occur. Normally labor begins when the fetus is old enough to be able to maintain itself from intrauterine life to extrauterine life. The childbirth process consists of 4 phases, the first phase is called the opening, where the cervix ripens and opens up to a completely about 10 cm.
The second phase is also called when the expenditure with the mother’s strength is adequate so that it can encourage the baby to be born soon. Third phase or when the placenta is born from the uterine wall of the mother. The fourth phase starts from the placenta born to 2 hours postpartum.
The first stage of childbirth lasts from the occurrence of regular uterine contractions to complete cervical dilation. Clinically, it can be stated that labor starts when the mucus arises and comes out mixed with blood. Mucus mixed with blood originates from capillaries around the cervical canal which rupture due to shifts when the cervix opens.
Physiologically, when the gestational age is mature enough, a series of symptoms arise to give the signal for starting the labor. Various factors indicate the time of labor. These factors work together to produce a very strong, regular, rhythmic uterine contraction that ends with the birth of the fetus and placenta. Here we have submitted some factors indicating the time of labor:
- Stretching of the uterine muscles, with increasing gestational age, the capacity of the uterus increases and the muscles of the uterine wall become increasingly tense. This condition causes mechanical stimulation in the form of uterine contractions.
- The pressures on the cervix. This condition stimulates oxytocin release and normally causes uterine contractions.
- Oxytocin stimulation. At the end of pregnancy, oxytocin levels increase and the uterine muscles are very sensitive to the effects of oxytocin. Oxytocin works with prostaglandins to cause contractions.
- Changing the ratio between the hormones estrogen and progesterone gradually decreases at the end of pregnancy, finally, this can stimulate uterine contractions.
- Age of the placenta. The process causes chorial villi to undergo changes so that progesterone and estrogen levels decrease. This stimulates uterine contractions.
- Increased fetal cortisol levels. This causes a decrease in the formation of progesterone and increased prostaglandins which stimulate the emergence of uterine contractions.
- This condition is also indicated by the fetal membrane produces prostaglandin. This condition is stimulating uterine contractions.
The conditions that are considered physiological in the first stage of labor are as follows:
The length of labor varies greatly and is influenced by maternal parity, psychological state, shape, and size of the abdomen, as well as the character of the uterine contraction. Most of all stages of labor are processes from the first stage, and it is generally expected that the active phase will end within 12 hours.
- Uterus action
Every uterine contraction always starts from the fundus near one of the corners and spreads down. The contraction lasts the longest and the strongest fundus at the same time but reaches its peak simultaneously throughout the parts. This pattern allows the cervix to open and the fundus to contract adequately. Finally, this process can expel the fetus.
- Contractions and retractions
The uterine muscles have a unique trait. During labor, the contraction does not fully continue but the muscle fibers retain some of the shortenings of the contraction. These are not fully called retraction. This action helps progressively dislodge the fetus, the upper segments of the uterus slowly change to become shorter and thicker and the sockets shrink. At the start of labor, the uterine contractions occur every 15-20 minutes and can last approximately 30 seconds. These contractions are only a little weak and can not even be felt by the mother. These contractions usually occur with rhythmic regularity and the intervals between contractions progressively become shorter, while the length of the contraction is longer. At the end of the first period, the contractions can occur 2-3 minutes in time and last for 50‐60 seconds. Their characteristics are very strong.
- Formation of the upper and lower segments of the uterus
At the end of pregnancy, the uterus is divided into two segments. These are anatomically different. The upper uterine segment is mainly associated with contraction, thick and muscular while the lower segment is prepared for inflating and opening and thinner. The lower segment has developed from the isthmus and approximately 8-10 cm long. When labor begins, longitudinal fibers, retract in the upper segment, will attract the lower segment which causes it to widen.
- Retraction Ring
A line will form between the upper and lower segments known as retraction rings or bandle rings. Usually, we use the first term to describe a physiological retraction ring and only use the term ring for a certain degree of excessive symptoms that will be seen above the symphysis pubis at slow labor. The normal retraction ring will slowly rise as the upper uterine segment contracts and retracts while the lower uterine segment will thin out to accommodate the fetus. This decreases after the cervix has fully opened.
- Thinning of the cervix
The muscle fibers surrounding the opening in the cervical neck will be pulled upward by the retracted upper segment and the cervix fused into the lower uterine segment. The cervical canal’s characteristic is wide and flat. In primigravida, the outer cervix will remain closed until the cervix flattens above the fetus and all will thin out, whereas in the multigravida the cervix will begin to open before completed thinning. In women who have high parity, their cervix may never fully thin out.
- Cervical opening
The cervical opening is the process of enlarging the end of the cervix from a tightly closed state to open. This condition occurs to reach the large enough for allowing the passing of the fetal head. The opening is measured in centimeters and will complete in 10 cm. This process will occur as a result of pressure on the uterus by the fetus. Pressure in the uterus will cause the uterine fundus to react by contracting.
As a result of opening the cervix, the woman giving birth will release blood. The blood will sprinkle with mucus or it can be just blood. The blood comes from the fine vessels that rupture within the parietal decidua and also from the opened cervix. This blood count should not be more than 500 ccs. If active bleeding occurs, it is considered abnormal.