1. Parturition

2. Parturition Parturition means giving birth
Labor is the process of expelling the fetus
Strong contraction of the uterus
Expulsion of the baby
Two important factor
Progressive hormonal changes →↑excitability
Progressive mechanical changes →↑ stronger and stronger contraction

3. Hormonal factors Progesterone →↓excitability and contractility
Estrogen →↑ excitability and contractility
During the early 30 weeks of pregnancy estrogen to progesterone ratio is balanced
After about 30th week
Estrogen continues to increase
Progesterone reaches a stationary level
E/P is increased
Contractility progressively increases
Labor begins when progesterone’s inhibition is overcome by an increase in the levels of estrogen

4. Hormones in pregnancy

5. Human chorionic gonadotropin (hCG)
Estrogen
Progesterone
Fertilization
Delivery

6. Hormonal factors Oxytocin
Oxytocin has been proved to be involved in increased contraction of the uterus
Oxytocin receptors in uterine muscles increase in the later part of the pregnancy
Rate of oxytocin secretion has been seen to be high at the time of delivery
Absence of posterior pituitary → prolonged labor
Experimental irritation or stretching of the cervix increases the production of oxytocin

7. Hormonal factors Fetal hormones
Fetal posterior pituitary produce large amount of Oxytocin
Fetal adrenal cortical Cortisol is also oxytocic
Prostaglandins from the fetal membranes toward the end of pregnancy help the contractility during labor

8. Mechanical factors Stretch of the uterine musculature
Stretch of any smooth muscular organ → ↑ contractility
Movements of the fetus → intermittent contractions
Faster growth and more stretch of the uterus towards the end of the pregnancy → stronger contractions
Twins → more stretch → early birth

9. Mechanical factors Stretch or irritation of the cervix
→ local mechanism for stronger contractions of the uterus
Irritation of nerves in the cervix initiates local response to cause reflex contraction of the body of the uterus
ARM is helpful in induction of labor
May be local myogenic transmission of signals from the irritation of the cervix → contraction of the body of the uterus

10. Onset of labor
Braxton Hicks contraction throughout the pregnancy – weak contractions
Force progressively increases in later pregnancy
Sudden strong contraction initiate the cervical stretch → labor contractions
A +ve feed back mechanism of increase contraction starts
Every succeeding cycle of cervical stretch → stronger contraction than the preceding cycle
Strong contraction → head of the baby pushed more into cervix → stronger stretch → stronger contraction

11. Onset of labor Two types of +ve feed backs
Labor contraction → Stretching of cervix → stronger labor contraction of the body → more stretching of the cervix →…. →…. →…
Labor contraction → Stretching of the cervix → oxytocin production → stronger labor contraction →…. →… →….

12. Uterine contractions Push fetus against cervix (through neuroendocrine
reflex)
Oxytocin
secretion
Prostaglandin
production
Responsible for
progression of
parturition

13. True Versus False Labor
True labor contractions
Each contraction increases the cervical stretch
Each new cycle of +ve feed back is stronger than the previous one
False labor contractions
When contraction is not strong enough to cause +ve feed back stronger contraction
The contraction gradually fade away

14. Abdominal muscle contractions
Pain signals from the uterus and birth canal
→ neurogenic reflexes in the spinal cord
→ abdominal muscle contraction
→ ↑ intra abdominal pressure
Help the expulsion of the baby

15. Mechanics of parturition
Each labor contraction begins at top of the body of the uterus the spreads downwards
Contraction is stronger at the top
So each contraction pushes the baby into the lower segment of uterus and cervix
Frequency :- strong contraction occurs
Initially every 30 – 40 minutes
Progresses to every 1-3 minutes
Strength of contraction also increases as the labor progresses
A force of 25 pounds pushes the baby in strong contractions

16. +ve feedback mechanical cycle

17. Intermittency of labor contraction
Contractions are intermittent
Contraction are not continuous
There is period of relaxation in between contractions
Continuous contraction may cause severe ischemia of the fetus because of obliteration of the blood vessels by contacting myometrium
Spastic contraction of uterus may lead to death of the fetus

18. Stages of labor 1st stage Stage of dilation
From onset of labor to the complete dilation of the cervix
6-24 hours in first pregnancy
Duration shortens with multiple pregnancies
May be only a few minutes
Cervix softens and dilated by the presenting part (usually head)
Rupture of amniotic sac

19. 1st stage of labor
Partially dilated cervix

20. Stages of labor 2nd stage Stage of actual delivery of the baby
Baby passes through the birth canal
Uterus, cervix and vagina all lined up to form birth canal
Maximum strong contraction of uterine muscles aided by abdominal muscle contraction
Maximum force exerted for expulsion
10 minutes to a few hours

21. 2nd stage of labor

22. Stages of labor 3rd stage Delivery of placenta
minutes after birth
Uterus contracts to smaller size
Wall of the uterus contracts, placenta does not contract (Shearing effect)
Separation of placenta
Bleeding from the site
Average blood loss 350 ml
Contraction of uterus reduces the bleeding
Local prostaglandins also cause vasoconstriction

23. 3rd stage of labor
Placenta
Umbilical cord
Uterus

24. Stages of labor Placenta Umbilical cord Partially dilated cervix
Uterus
First stage of labor:
Cervical dilation
Second stage of labor:
Delivery of the baby
Third stage of labor:
Delivery of the placenta

25. Labor pains Each contraction is accompanied by pain
Cause – hypoxia of the uterine muscle
Hypogastric nerve (visceral nerve) carries the sensation
2nd stage of labor more severe pain due to
Stretching and tearing of cervix, vagina, and perineum around
Somatic spinal nerve conduct the sensation

26. Involution of uterus Involution within 4-5 weeks after parturition
Weight of uterus is ½ of weight after delivery just within one week after parturition
In nursing mother uterus is as small as prior to pregnancy within 4-5 weeks
During early involution vaginal discharge from the placental site- lochia for about 1½ - 2 weeks
Initially Bloody
Then becomes Serous
Then the endometrium is completely re-epithelialized
Discharge disappears

27. Thank-you
Questions ??