Parturition: Stages and Hormones of Parturition

Parturition is also known as childbirth. Labour is a physiological process during which the foetus, its associated membranes, the umbilical cord, and the placenta are expelled from the uterus. This article covers the different stages of parturition, the onset of parturition, hormones involved in parturition and much more. Read the article to know more about Parturition.

What is Human Parturition?

Parturition is also called childbirth. It is the act of expelling the full-term young one from the mother’s uterus at the end of gestation. The series of changes that brings the onset of labour is termed parturition. Gestation in humans is completed in about \(280\) days from the mother’s last menstruation. Lactation begins after the birth of a baby, and the first milk is called colostrum.

Fig: Parturition

Signs and Changes During Parturition

Some of the signs and changes that occur during Parturition are as follows:

1. Mucous discharge
2. Bloated abdomen
3. Feeling relentlessness
4. Change in the hormonal levels of the body
5. Labour and Contractions of the myometrium of the uterus
6. Fully swollen vulva
7. Relaxed pelvic ligaments
8. Lactation.

Parturition Hormones Involved

The process of parturition is initiated by a complex neuroendocrine mechanism. The signals for parturition originate from the placenta and fully developed foetus, which induce mild uterine contractions called foetal ejection reflex. The hormones involved in the process of Parturition are as follows:

1. Oxytocin

i. It is also known as the birth hormone or milk-secreting hormone.
ii. Foetal ejection reflex triggers the release of oxytocin from the posterior pituitary of the mother.
iii. The amount of oxytocin is increased just before and during labour pains.
iv. Oxytocin (birth hormone) induces the contraction of the smooth muscles of the myometrium of the uterus.
v. The contraction of the myometrium acts as the positive feedback regulation and a stimulus for increased secretion of oxytocin.
vi. Thus, gradually levels of oxytocin in the blood increase, which in turn increases the strength of uterine contraction and thus leading to parturition.
vii. Oxytocin also causes the development of milk-ejection reflex (MER), which causes the secretion of milk from the mammary glands.

Fig: Foetus-Ejection Reflex

2. Relaxin

i. In the initial stages of pregnancy, relaxin inhibits myometrial contraction and stabilizes the pregnancy.
ii. Relaxin increases the flexibility of the pubic symphysis by softening the connective tissue and ligaments of the sacroiliac and sacrococcygeal joints.
iii. It helps to dilate the uterine cervix during labour pains.

3. Corticotropin-releasing Hormone (CRH)

i. Corticotropin-releasing hormone (CRH) is released by the placenta during pregnancy, which in nonpregnant women is secreted only by neurosecretory cells of the hypothalamus.
ii. CRH acts as the “clock” that establishes the timing of birth.
iii. High levels of CRH during the early stages of pregnancy in a woman can result in premature pregnancy delivery, whereas those who have low levels are more likely to deliver after their due date.
iv. CRH regulates the timing of birth by altering the signalling pathways and systems that are responsible for controlling the contractile properties of the smooth muscles of the myometrium of the uterus.
v. Secretion of CRH by the placenta increases enormously, usually \(1000-10000\) times more than a normal and nonpregnant woman.

Parturition Diagram

The process of parturition and the stages are shown in an image/diagram below:

Fig: Stages of Parturition

What are the Three Stages of Parturition?

The stages of vaginal parturition include three stages, i.e., dilation, expulsion and placental.

1. Dilation Stage

This is the first stage of parturition. It is the time period from the onset of labour pain to complete dilation of the cervix.
This stage is divided into a latent phase, an active phase and a transition phase.

a. Latent Phase

i. This phase lasts about \(6\) to \(12\) hours.
ii. The latent phase or early labour phase begins with mild, irregular uterine contractions that soften and shorten the cervix.
iii. As contractions begin, the walls of the uterus start to contract through stimulation by the release of the hormone oxytocin secreted from the posterior pituitary.
iv. The contractions cause the cervix to widen and begin to open.
v. It results in the discharge of fluid and a bit of abdominal discomfort.
vi. The water may break, i.e., rupture of the amniotic sac membrane or amnion takes place, and it flows out through the vagina.

b. Active Phase

i. The active phase of the dilation stage generally lasts up to \(3\) to \(6\) hours.
ii. This phase begins when the cervix is about \({\rm{3 – 4}}\,{\rm{cm}}\) dilated.
iii. The active phase is characterized by further dilation of the cervix and descent of the fetal part towards the cervix.
iv. Contractions become progressively more rhythmic and stronger.

c. Transition Phase

i. It lasts for \(20\) to \(30\) minutes, and contractions are initiated at an interval of about every \(1\) to \(3\) minutes.
ii. The contraction of the myometrium is very intense.
iii. Cervix dilates from \(7\) up to \({\rm{10}}\,{\rm{cm}}\) i.e., complete dilation.

2. Stage of Expulsion of Baby

1. This stage is the second stage of partition and lasts between \(20\) minutes to several hours.
2. During this stage, the baby is pushed out of the uterus and down the cervix and vagina (together called the birth canal), usually head first, followed by the rest of the body.
3. The foetus is expelled from the uterus by the combined forces of the smooth muscles of the myometrium of the uterus and the contractions of the muscles of the abdominal wall.

3. Placental and Umbilical Cord Expulsion Stage

1. This stage is the third and the last stage of parturition, which lasts for about \(10\) to \(15\) minutes after the birth of the child.
2. It is the time after the delivery until the placenta or after birth is expelled by powerful uterine contraction.
3. Contractions of blood vessels of the uterus and blood flow through the umbilical cord ceases.
4. The umbilical cord is clipped close to the baby’s navel, and once the baby is breathing normally.
5. The newborn baby’s skin is bluish pink in all human races as the pigment is made after exposure to sunlight.

Summary

Parturition is an interesting biological process that takes place in the pregnant woman during the last stage of pregnancy and is also called childbirth. The series of changes that brings the onset of labour is termed parturition. This process involves synchronized interactions between the foetus and the maternal system and is a complex neuroendocrine mechanism.

Signals for parturition originate from the fully developed foetus and the placenta, which induces mild uterine contraction and is called foetal-ejection reflex. The phases of parturition can be divided into three phases, i.e., dilation of the cervix, the expulsion of the baby and expulsion of the placenta and umbilical cord.

Frequently Asked Questions (FAQs) on Parturition

Q.1. What is human Parturition?
Ans: Parturition, also called childbirth, is the process of giving birth to a child. The onset of parturition is by a complex neuroendocrine mechanism.

Q.2. What are the \(3\) stages of parturition?
Ans: The phases of parturition can be divided into three phases, i.e., dilation of the cervix, the expulsion of the baby and expulsion of the placenta and umbilical cord.

Q.3. Which stage of parturition is usually the longest?
Ans: The first stage of labour, i.e., the dilation of the cervix, is the longest stage, and it can last for more than \(12\) hours.

Q.4. Why is oxytocin given during labour?
Ans: Oxytocin or its chemical derivative Pitocin injection is used to begin or improve myometrial contractions during labour. Oxytocin also facilitates milk secretion from the mammary glands.

Q.5. What are the signs of parturition?
Ans: The signs of parturition are follows:
a. Mucous discharge
b. Bloated abdomen
c. Feeling relentlessness
d. Change in the hormonal levels of the body
e. Labour and Contractions of the myometrium of the uterus
f. Fully swollen vulva
g. Relaxed pelvic ligaments
h. Lactation.

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