SPR L7 Pregnancy, Labour and Lactation Flashcards Preview

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Flashcards in SPR L7 Pregnancy, Labour and Lactation Deck (18)
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Learning Outcomes

for general perusal

  • To elucidate the importance of Reproduction to the human
  • To discuss how the physiologic challenge of the foetus is met by the mother
  • To outline the process of parturition in the run up to and during the birth process
  • To describe the processes underlying lactation and milk ejection

Concepts and Learning Objectives

  • The developing embryo/foetus presents quite a significant physiologic challenge to the mother which is met by the cardiovascular, respiratory, gastrointestinal, endocrine and renal systems.
  • The birth of a baby (parturition) occurs in 3 stages.  Initially the cervix becomes dilated, then the foetus is expelled after which the placenta is also delivered.
  • During puberty the breasts develop as potential milk secreting organs, and this process is completed during pregnancy, and obviously after birth.  It involves interplay of several hormone systems involved both in breast development and milk letdown.


Meeting the Challenge

Give examples of physiologic adaptations and phenomena resulting from the challenge placed on the maternal physiology by the developing foetus

  • Morning Sickness
  • Cardiac output increases to 30 -40% by 20 weeks gestation
  • VO2 and VCO2 also increase 
  • 15% increase in BMR
  • rise in respiratory minute volume of a similar magnitude (about 20%)
  • Renal reabsorption of NaCl and H2o is elevated
  • GFR is also raised both directly and indirectly
  • possibly an increase in frequency of urination.
  • an additional 1g iron is needed over the course of a pregnancy over and above normal need
  • Dyspnoea sometimes results in late pregnancy, along with acid reflux
  • Maternal weight gain is about 10Kg


Meeting the Challenge - Maternal Physiologic Adaptations

Morning Sickness

  1. When in the pregnancy is this a feature?
  2. What is it probably due to?
  3. When is the initial peak, what happens after?

  1. early pregnancy
  2. the rise in human chorionic gonadotropin (hCG). 
  3. First trimester. Tends to diminish after this.


Meeting the Challenge - Maternal Physiologic Adaptations

Cardiac Output

  1. By how much does it increase?
  2. By when?
  3. By how much does blood volume rise? When does this occur?

  1. increases by 30-40%
  2. by 20 weeks gestation
  3. by 20%, with most of the increase coming in the second half of pregnancy


Meeting the Challenge - Maternal Physiologic Adaptations

VO2 and VCO2

  1. What happens to these and why?
  2. What are the effects on BMR at term?
  3. What are the effects on respiratory minute volume?

  1. increase in the same time period, with the demands of the foetal metabolism
  2. a 15% increase in BMR in the female at term
  3. a rise of about 20% (which makes sense because ventilation tracks metabolic rate).


Meeting the Challenge - Maternal Physiologic Adaptations


Renal Reabsorption of NaCL and H2O

  1. What happens to these and why?
  2. What happens to GFR?
  3. What causes the increased frequency of urination?

  1.  elevated by the mineralocorticoid like effects of the maternal sex steroids which are at high levels throughout pregnancy
  2. raised both directly and indirectly (by the increased CO) to limit the resulting fluid retention.
  3. The third trimester is also marked by the foetus pressing on the bladder which may increase frequency of urination.


Meeting the Challenge - Maternal Physiologic Adaptations


  1. What intake may not be adequate for the nutritional demands of pregnancy in general?
    1. Give an example
    2. What can a pregnancy woman be prone to?
  2. What is corrected by demineralising maternal bones?

  1. energy and protein intake in the average female diet is generally adequate but mineral and vitamin intake may not be
    1. Eg, an additional 1g iron is needed over the course of a pregnancy over and above normal need.  Body stores of iron are only 100 – 700 mg, meaning a pregnant woman is prone to anaemia. 
    2. calcium deficiency  

This is a general principle; nutritionally the foetus comes first.


Meeting the Challenge - Maternal Physiologic Adaptations

Dyspnoea and Acid Reflux

  1. ​When do these occur?
  2. Why?

  1. in late pregnancy
  2. both due to the mechanical effects of the foetus situated in the abdomen where it is.


Meeting the Challenge - Maternal Physiologic Adaptations

  1. What is the magnitude of maternal weight gain?
  2. When does this take place?
  3. What does it consist of?

  1. about 10Kg
  2. mostly in the third trimester
  3. consisting of foetus (3.5Kg), placenta and amniotic fluid (2.5Kg), Breast development (1Kg) and the increased body weight in the mother (2/3 fluid) (3.5 Kg).



  1. How long does pregnancy last on average in days?
  2. What are the three stages of parturition (birth)?
  3. What needs to occur before birth to facilitate these changes?

  1. about 270 days (284 days from the last menstrual period). 
  2. 3 stages: dilation of the cervix, expulsion of the foetus and delivery of the placenta.
  3.  a number of hormonal changes happen to facilitate its succcess




Before Birth

  1. What happens to the cervix under the influence of relaxin?
    1. What else becomes more flexible?
  2. What happens under the influence of increasing oestrogen levels?
  3. What happens to prostaglandin production? What is the purpose of this?
  4. What hormone production is increased in the foetus itself during this time?
    1. What does this have a positive feedback effect upon?
  5. What is the cortisol thought to be vital to the maturity of?

  1.  normally firm, it softens and dilates in preparation for the birth
    1. while the pubic symphysis also becomes more flexible.
  2. smooth muscle of the uterus becomes more excitable and more connected by gap juntions.
  3. increases, and the number of oxytocin receptors also rises (about a 100 fold rise during pregnancy).  This prepares the myometrium for its impending task.  (These changes may underlie the irregular uterine contractions that occur in the last trimester)
  4. CRH (corticotrophin releasing hormone) production is increased during this time
    1. on placental feedback production, increasing foetal ACTH and cortisol
  5. this cortisol is thought to be vital to the final maturity of the foetal respiratory system, preparing it for its drastic change in environment. 

In effect the foetus picks the time to be born by increasing its own CRH production.




 Birth - 1) Dilation

  1. How long does this stage last?
  2. What happens in this stage?
  3. What does the stretch cause?
  4. What else stimulates myometrial contraction?
  5. What is important in increasing flexibility of the cervix and pubic symphysis?

  1. 8-24 hrs
  2.  the canal through the cervix is dilated by the action of the babies head pushing down on it by myometrial contractions.
  3. a reflex release of oxytocin from the posterior pituitary which acts on an myometrium already very sensitive to oxytocin to further increase contraction, increasing cervical stretch, thus positively feeding back and amplifying the contractions. 
  4. Prostaglandins
  5. relaxin 



 Birth - 2) Expulsion

  1. When does this second stage begin?
  2. What triggers the reflexes, and what are these?
  3. What can the reflex contractions be reinforced voluntarily by?
  4. How long does this phase last?

  1. when the cervix is fully dilated to 10 cm.
  2. The head exiting the cervix triggers reflexes which contract abdominal muscles to help expel the baby through the vagina.
  3. consciously pushing with them.
  4. between 30 and 90 min


 Interestingly, the conscious “bearing down” with the abdominal muscles, although it can aid in birth, isnt strictly speaking necessary, since paraplegic women can successfully give birth.



Birth - 3) Delivery of the Placenta

  1. What happens in this stage?
  2. What is there a risk of?
  3. Following delivery, what is there a dramatic drop in hormonally? Why?
    1. What does this lead to?
  4. What keeps the maternal part of the placenta from coagulating before this stage?
  5. How long does the pre-pregnancy state last for?
  6. What is the average labour time for the first baby?

  1. delivery of the placenta, which shears off the wall of the contracted uterus.
  2. risk of blood loss here, but it is normally quite minimal (300 – 400 ml) because the uterus is already quite contracted.
  3. maternal oestrogen and progesterone due to the loss of the placenta which had been manufacturing them and the corpus luteum of pregnancy (which relies on hCG to sustain it). 
    1. a regression of the decidual endometrium giving a discharge post birth termed Lochia
  4. Chorionic anticoagulants - This is gone so coagulation takes place.
  5. 4-6 weeks
  6. 6 hours





  1. During pregancy the breasts develop to become milk secreting organs under the influence of what?
  2. What does oestrogen promote?
  3. What does progestrone enlarge?
  4. What acts to develop the enzymes necessary for successful milk production?
  5. When is a female fully capable of producing milk?
    1. What is this prevented by before birth?


  1. the increased amounts of oestrogen and progesterone from the placenta.
  2. duct development
  3. the terminal, secretory portions of the glands (the alveoli). 
  4. Prolactin from the mothers anterior pituitary gland and human chorionic somatomammotropin (HCSM) (a general anabolic hormone, sometimes termed “the maternal growth hormone of pregnancy) from the placenta
  5. About 20 weeks into pregnancy
  6. the high levels of oestrogen and progesterone  As described above, however, these drop with birth.

 [AS1]Sometimes referred to the ‘growth hormone of pregnancy’



  1. What allows lactation and milk let down to proceed after delivery?
  2. What are both of these processes classed as, and what do they depend upon?
  3. What causes secretion of prolactin? How? What does this do?
  4. What does nipple stimulation also increase? And what does this cause?

  1. oestrogen and progesterone levels fall
  2. Both processes are neuroendocrine, depending on both nervous afferents and endocrine effectors. 
  3. Mechanical stimulation of the nipple by decreasing the secretion of prolactin inhibitory hormone (PIH), although prolactin releasing hormone (PRH) may also be involved to a lesser extent.  This initiates and maintains milk production.
  4. oxytocin output from the hypothalamus (released in the posterior pituitary; a genuine neuroendocrine reflex), which causes contraction in the smooth muscle surrounding the secretory alveoli and expels milk.


Interestingly breast feeding can act as a (slightly unreliable) contraceptive since prolactin inhibits GnRH production.

(Neuroendocrine: Advantages for this being neural = instantaneous, Endocrine = whole organ involved)

Hormones released in breastfeeding is important in bonding 


Components of Breast Milk

  1. What does normal breast milk contain?
  2. What about in the first few days after birth?

  1. triglycerides, carbohydrate in the form of lactose, protein, vitamins, calcium and phosphate. 
  2. humans secrete colostrum which has more protein and less fat and lactose. Colostrum also contains lactoferrin, an antibacterial, and maternal antibodies of the IgA type, providing passive immunity.


Summing Up

For general perusal 



  • A successful pregnacy depends on the mother meeting the significant physiologic demands of the embryo/foetus
  • Throughout pregnancy the endometrium is preparing for birth which takes place in 3 stages
  • Lactation is supported by neuroendocrine systems that promote milk production and letdown

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