Childbirth

Question 1

How can urinary incontinence be caused by damage to the pelvic floor?

Answer 1

Affects 50% of 40yr+ women

Continent = urethra above pelvic floor —> increased intra-abdominal pressure affects bladder & urethra equally

Incontinent = neck of bladder falls through urogenital hiatus —> increased intra-abdominal pressure affects body of bladder only —> stress incontinence

note: puborectalis forms a sling around the large intestine (anorectal flexure, ~80 degrees), which compresses the urethra against the pubic symphysis

Question 2

How can pelvic floor damage cause faecal incontinence?

Answer 2

Medial part of puborectalis (inserts into perineal body as a pubo-vaginalis muscle) —> herniation of rectum (tear extends into external anal sphincters) —> difficulty with defecation/faecal incontinence

Question 3

What is an episiotomy?

Answer 3

Incision made in perineum around the vagina to avoid tearing of adjacent muscles & perineal body (enlarges opening in a controlled manner)

Medio-lateral incision (~45-60 degrees) on right side (NOT MIDLINE!)

note: more common now to allow tearing to occur as it will tear along normal lines and therefore heal more easily

Question 4

Give some examples of complications of childbirth.

Answer 4

• stress incontinence
• stretched pudendal nerve —> muscle weakness & neuropraxia (temporary loss of motor/sensory function due to blockage of nerve conduction)
• stretch/damage to pelvic floor/perineal muscles (e.g. avulsion from pelvic wall) —> muscle weakness
• stretch/rupture of ligaments supporting muscles —> ineffective muscle action

Question 5

What are some risk factors for pelvic floor damage?

Answer 5

• age
• menopause (oestrogen withdrawal —> tissue atrophy)
• obesity
• chronic cough (bronchiectasis)
• connective tissue laxity

Question 6

How can prolapse due to childbirth be repaired?

Answer 6

Remove prolapsed organs, restore connective tissue supports

Suture ruptured vagina & perineum

Complications:

• recurrence (10%-15%)
• new incontinence
• dyspareuria

Question 7

What is the difference between labour and parturition?

Answer 7

Labour = expulsion of products of conception after 24 weeks

Parturition = labour in animals

Question 8

What are the three stages of labour?

Answer 8

1. Creation of birth canal
2. Expulsion of foetus
3. Expulsion of placenta & contraction of uterus

Question 9

Describe how the uterus changes in size during pregnancy.

Answer 9

12wks = uterus superior to pubic ramus (therefore palpable)

20wks = uterus reaches umbilicus

36wks = uterus reaches xiphisternum

Question 10

What is the approximate size and weight of a term baby?

Answer 10

~3-4kg

~30-45cm long

Question 11

What is meant by the lie of the baby during birth?

Answer 11

Relationship to long axis (vertebral column of mother) of the uterus

Normally longitudinal = parallel to the vertebral column of the mother

Foetus normally flexed (similar to brace position) - “attitude” of baby

Question 12

What is meant by the presentation of the baby during birth? Give some examples.

Answer 12

Which part of the baby is adjacent to the pelvic outlet

Normally cephalic:

• vertex = ~9.5cm
• sinciput = ~10cm
• brow = ~13.8cm
• face (baby extended) = ~9.5cm

Sometimes podalic (buttocks - “breech” presentation):

• frank breech = legs up with arms wrapped around them
• full breech = curled up
• single footling breech = foot goes through cervix (may not dilate any wider than the foot, so C-section may be required)

Question 13

What is meant by the position of the baby during birth?

Answer 13

Orientation of presenting part of baby (how the baby is rotated)

Most commonly rotated so that the vertex to pelvic inlet is at a minimum diameter (smallest part of the head is presented)

Question 14

What determines the maximum size of the birth canal? What size is required for passage of the baby?

Answer 14

Pelvis:

• transverse diameter & inlet = ~13.5cm
• interspinous diameter = ~10cm
• obstetric conjugate = ~10.5cm (pelvic inlet)

Softening of ligaments & expansion of soft tissues allows distortion to increase the maximum size of the birth canal to 10cm

Normal presentation baby (i.e. head is biggest part - biparietal diameter) = ~9.5cm diameter

Question 15

How are the soft tissues expanded to increase the diameter of the birth canal?

Answer 15

Cervical ripening = softening of cervix triggered by prostaglandins produced by the endometrium

Also stimulated by increase in oestrogen (changes oestrogen:progesterone ratio —> stimulates prostaglandin increase, increases no. of smooth muscle receptors, increases gap junction communication between smooth muscle cells) & relaxin

Causes a reduction in collagen & a reduced aggregation of collagen fibres (less tightly wound) and an increase in glycosaminoglycans (increased ratio of glycosaminoglycans:collagen)

note: no consistent evidence of oestrogen:progesterone changes e.g. foetuses with no adrenal glands can be born

Question 16

Describe the contractions which occur during pregnancy and how this changes to initiate labour.

Answer 16

Uterine contractions occur throughout pregnancy:

• early = low amplitude; approx. every 30min (mother usually unaware)
• late = higher amplitude; more frequent (Braxton-Hicks contractions = practice contractions - mild cramping)

Prostaglandins increase the force & freq. of contractions (increased calcium released per AP) - synthesised by amnion in trimester 3

Myometrium is thickened in pregnancy (increased force). Multiple APs triggered spontaneously (pacemakers) at regular intervals to ensure all of the uterus contracts at once

Oxytocin lowers the threshold for APs —> increased amount of APs

Ferguson reflex = positive feedback mechanism by which oxytocin secretion is increased by afferent impulses from cervix and vagina

note: oxytocin action inhibited by progesterone, relaxin, & low no. of oxytocin receptors (at term the no. of oestrogen receptors in the myometrium increase)

Question 17

How does the uterus drive the presenting part of the foetus to the cervix during labour?

Answer 17

Brachystasis = uterus relaxes less than it contracts —> permanent shortening of fibres (preventing baby “springing back” into place between contractions)

Reduces uterine capacity & increases the pressure in the uterus

Contractions created from two poles of uterus —> travel to fundus & upper uterus —> travel to lower part of uterus

note: contractions more powerful at the upper part of the uterus than the lower part
note: first time mothers more likely to have uncoordinated contractions

Question 18

When does labour begin?

Answer 18

Cervix thins & flattens (effacement) —> dilates —> rupture of amnion (“waters breaking” - ~1l)

Once cervix is dilated to 10cm the head of the foetus can fit and it can begin to be birthed

note: difference between cervical effacement (thinning of cervix) and cervical dilatation (opening of cervix)

Question 19

What are the steps of the expulsion of the foetus?

Answer 19

Rapid (up to 1hr)

Urge to “bear down” (additional force to outside of uterus e.g. abdominal muscles) to expel the foetus

Presenting part appears in birth canal (crowning)

When the baby is positioned normally:

1. Head flexes
2. Rotates internally (so max. diameter of head fits max. diameter of pelvis)
3. Head delivered, rotates & extends
4. Shoulders rotate and are delivered

Question 20

Describe how the placenta is expelled.

Answer 20

~10min

Increased uterine contractions —> shears off placenta from endometrium & uterus contracts down (becomes smaller) —> blood vessels opened by shearing are compressed by uterus

note: need to check that all of the placenta has been expelled
note: can give oxytocic drugs to stimulate contraction of the uterus to compress the blood vessels

Question 21

What are the 3 P’s of labour?

Answer 21

POWER = force of contractions

PASSENGER = foetus presentation

PASSAGE = pelvic inlet

Question 22

How do the shunts which exist in utero close after birth?

Answer 22

Ductus venosus = closed/removed with the umbilical vein (and atrophies)

Foramen ovale = increased pressure in lungs from first breath reverses pressure gradient in heart —> shuts foramen ovale —> fossa ovalis

Ductus arteriosus = smooth muscle detects increased pO2 —> contraction —> closes ductus arteriosus —> ligamentum arteriosum)

Question 23

What is respiratory distress syndrome?

Answer 23

Condition of newborn infant in which the lungs are imperfectly expanded due to insufficient surfactant

Also called hyaline membrane disease

Often affects premature babies

note: if preterm delivery is unavoidable, then give glucocorticoids to mother to accelerate surfactant production

Question 24

Why is it important for the effect of oxytocin on the myometrium to be suppressed until labour?

Answer 24

Progesterone prevents oxytocin from evolving contractions during pregnancy, which prevents spontaneous abortion

Progesterone also reduces uterine prostaglandin release, which reduces myometrial activity

Question 25

What foetal landmark is used to assess foetal head position in the birth canal?

Answer 25

Foetal fontanelles

Question 26

What foetal structures are at risk during delivery of the baby’s shoulders?

Answer 26

Brachial plexus

Question 27

What spinal segments are blocked during an epidural? Why is there a risk of hypotension during an epidural?

Answer 27

T9-S4

Lumbar sympathetic outflow blocked —> prevents vasoconstriction

Question 28

Define post-partum haemorrhage. What is the most common cause?

Answer 28

Blood loss >500ml after vaginal delivery

Uterine atony (loss of tone in uterine musculature)

note: if the uterus is firm on palpation, uterine atony is likely not to be the cause (could be retained placenta, or laceration/trauma to the genital tract)

Question 29

What is Sheehan’s syndrome?

Answer 29

Thrombosis of vessels supplying the anterior lobe of the pituitary secondary to severe haemorrhage —> necrosis of the anterior pituitary

Anterior pituitary increases in size during pregnancy, so it is susceptible to necrosis

note: the posterior pituitary is unaffected, as it has a relatively rich arterial blood supply