Stages of Pregnancy, Parturition and Lactation Flashcards
1
Q
Describe these terms with respect to delivery:
- At term
- Pre-term
- Post-term
A
- Term
- Between 37 and 42 completed weeks
- Pre-term
- Before 37 completed weeks
- Post-term
- Beyond 42 completed weeks
2
Q
What are the stages of pregnancy?
A
- First trimester - up to 12 weeks.
- Second trimester - 12-27 weeks.
- Third trimester - 28 weeks to term.
3
Q
Describe the development of the foetal genitalia and explain how sex is established.
A
- All early embryos have 2 primitive duct systems; Wolffian and Mullerian ducts have the potential to form male or female tracts.
-
In males:
- Wolffian ducts become reproductive tract
- Mullerian ducts degenerate
-
In females:
- Mullerian ducts become reproductive tract
- Wolffian ducts degenerate
- Development into male or female depends upon hormones secreted by foetal testes – testosterone (stimulated by human chorionic gonadotrophin from placenta) and Mullerian Inhibiting Factor Iinduces regression of Mullerian ducts).
- Without stimulus of male testicular hormones, Wolffian ducts regress, Mullerian ducts develop and foetus will develop female characteristics.
4
Q
What is the role of softening of the cervix during labour?
How does it happen?
A
- Caused by prostaglandins and possibly relaxin.
- Breakdown of cervical collagen fibres allows cervix to dilate during labour.
5
Q
What are the stages of cervical effacement?
A
6
Q
How is labour initiated?
A
- Increased oestrogen synthesis by placenta produces dose-dependent changes in the uterus.
- Oestrogen increases the density of oxytocin receptors in the myometrium.
- Maternal oxytocin does not rise - parturition is triggered by increased sensitivity to oxytocin.
7
Q
Describe the 1st stage of labour.
A
- Onset of regular contractions to fully dilated cervix.
- May take many hours
-
‘Latent phase’
- Onset of painful contractions 5-10 minute intervals.
- Cervical ripening and effacement.
- Cervix slowly dilating up to 3-4cm.
-
‘Active phase’
- From cervix 3-4cm dilated, more rapidly 0.5-1 cm / hour.
- Progressive increase in frequency and strength of contractions.
- Descent of the presenting part.
- Cervix dilates to 10cm to accommodate the baby’s head.
- Breech birth – another part of body approaches cervix first.
- Rupture of amniotic sac (maybe) - “waters break” - lubricates birth canal.
8
Q
Describe the 2nd stage of labour.
A
- Fully dilated cervix to birth.
- Takes ~30-90 minutes.
- Cervix fully dilated (10 cm).
- Contractions stronger at 2-5 minute intervals.
- Presenting part descends.
- Urge to bear down.
- Baby moves through cervix to vagina.
- Stretch receptors in vagina trigger contraction of abdominal wall to augment uterine contractions.
- Mother can voluntarily contract abs also (“push”).
- Ferguson reflex – stretching of the perineum/pelvic floor in late labour seems to stimulate oxytocin release.
- After birth, the baby is freed from placenta by cutting umbilical cord.
- Cord is tied and forms umbilicus.
9
Q
What is the Ferguson reflex?
A
A positive feedback loop.
10
Q
Desribe the 3rd stage of labour.
A
- Expulsion of the plancenta and membranes.
- Separation due to forceful uterine contraction and reduces size of placental bed which reduces bleeding
- Takes a few minutes to an hour or so (depending on management).
- Placenta separates from myometrium and uterine contractions cause it to be expelled– “afterbirth”.
- Myometrium contracts and prevents haemorrhage by constricting uterine blood vessels at site of placental attachment.
11
Q
Describe post-partum involution.
A
- Shrinkage of uterus to pre-pregnancy size.
- Takes 4-6 weeks.
- Induced by:
- Fall in oestrogens and progesterone levels after placenta is lost.
- Oxytocin which is released in response to breast feeding.
- Other physiological adaptations return to pre-pregnancy state in the days and weeks that follow birth.
12
Q
Describe the structure of the breast.
A
- Breast has a glandular structure:
- Each duct terminates in a lobule
- Lobule is made of milk producing glands - alveoli
- Milk is secreted from epithelial cells into lumen
13
Q
Describe the breast development associated with pregnancy.
A
- At birth, the breast consists of lactiferous ducts without any alveoli (also male breast).
- At puberty, under influence of oestrogens, the ducts proliferate and masses of alveoli form at the ends of the branches.
- During pregnancy under the influence of oestrogen, progesterone and prolactin the glandular portion of the breast undergoes hypertrophy replacing adipose tissue.
- From week 16 the breast tissue is fully developed for lactation but is quiescent awaiting activation.
- After parturition the breast produces colostrum before mature milk production begins.
14
Q
What are the triggers for breast development during pregnancy?
A
- During pregnancy:
- ↑ oestrogen ➔ duct development
- ↑ progesterone ➔ lobule formation
- Prolactin (anterior pituitary hormone) & human chorionic somatomammotropin (placental hormone) ➔ synthesis of enzymes for milk production.
- Prolactin also stimulates milk production after parturition.
- Stimulatory action of prolactin is blocked in later stages of pregnancy by high levels of oestrogen and progesterone.
- Immediately after parturition oestrogen & progesterone levels fall, allowing prolactin to induce milk production.
15
Q
What are the important cells types in lactation?
A
- Secretory alveoli / acini cells - produce milk, stimulated by prolactin.
- Contractile myoepithelial cells - surround each alveolus, stimulated by oxytocin.
18
Q
Describe the role of prolactin in the suckling reflex.
A
- Suckling stimulus inhibits the hypothalamic release of dopamine (PIF) and prolactin is released in proportion to the strength and duration of the suckling.
19
Q
Describe the role of oxytocin in the milk ejection reflex.
A
- Suckling stimulates neurones in the hypothalamus to synthesise oxytocin which is carried to posterior pituitary.
- The release of oxytocin into the blood stream acts on myo-epithelial cells in the alveoli – causing the ‘let down’ of milk.
- Conditioned reflex:
- Let down in response to the cry of the baby
- Oxytocin release is inhibited by catecholamines - stress can inhibit the reflex.
22
Q
Describe the mechanism of breast milk production.
A
