Labour and delivery

Question 1

Different names for the expulsion of the fetus and placenta depending on when this occurs

Answer 1

Prior to 24weeks post gestation = spontaneous abortion/ miscarriage

24 weeks after gestation = labour

Labour before 37th week of gestation = pre-term labour/ premature

Biological name for childbirth = parturition

Question 2

What are the 3 stages of labour roughly and when does each stage end

Answer 2

1. Creation of birth canal, release of structures which normally retain the fetus in utero, enlargement and realignment of cervix and vagina (Ends when cervical dilation reaches 10cm)
2. Expulsion of fetus
3. Expulsion of placenta and changes to minimise blood loss from mother

Question 3

When does the uterus first become palpable, where has it reached by 20 and then 36weeks?

Answer 3

12 weeks

20 weeks - reached the umbilicus

36 weeks - reached the xilhisternum

Question 4

What is the ‘lie ‘ of the fetus?

Answer 4

Relationship between long axis of the fetus to the king axis of the uterus, commonest lie is longitudinal with head or buttocks posterior, fetus normally flexed attitude

Question 5

What is the ‘presentation’ of the fetus?

Answer 5

Which part of the fetus is adjacent to the pelvic inlet, if the baby lies longitudinally the presenting part may be the head (cephalic) or the breech (podalic)

Question 6

What aids widening And creation of the birth canal and what limits this?

Answer 6

True diameter of this inlet about 11cm (first stage of labour ends when cervical dilation reaches 10cm)

• softening of pelvic ligaments allows some expansion
• cervix must dilate and be retracted anteriorly (fetal membrane ruptures -> amniotic fluid released)
  facilitated by prostaglandins (E2 and F2alpha) -> cervical ripening (reduction in collagen and increase glycosaminoglycans which decrease aggregation of collagen, influx inflammatory cells, increased nitric oxide)
  but caused by forceful contractions of uterine smooth muscle which first thin the cervix (effacement) then dilate it

Limited by pelvis boundaries: posterior - sacral promontory, laterally- ilio -pectinal line, anteriorly - superior pubic rami and upper margin of pubic symphysis

Question 7

How do uterine smooth muscles carry out contractions?

Answer 7

Myometrium gets much thicker in pregnancy due to hypertrophy and glycogen deposition

Some smooth muscle cells capable of spontaneous depolarisation and action potential generation act as ‘pacemakers’ -> increase intracellular Ca2+ -> APs spread via gap junctions -> coordinated contractions

Myometrium Always spontaneously motile

Question 8

How do uterine contractions change throughout pregnancy and in labour?

Answer 8

In early pregnancy contractions may occur every 30mins, the frequency falls with some increase in amplitude, producing noticeable ‘Braxton-Hicks’ contractions -> onset of labour = sudden increase in frequency and force of contractions caused by:

• prostaglandins (enhance release of ca2+ from IC stores) increase
• oxytocin (from PPG - lowers threshold for triggering APs) increased sensitivity

As contractions increase - Ferguson reflex - increases oxytocin secretion massively ‘+ve feedback’

Question 9

What is brachystasis and why is it useful?

Answer 9

Brachystasis - at each contraction muscle fibres of uterine smooth muscle shorten but don’t fully relax (uterus shortens progressively) -> pushes the presenting part into the birth canal and stretches the cervix over it (descent of presenting part occurs progressively)

Question 10

What does animal evidence suggests initiates labour?

Answer 10

forcefuk contractions -> reduce placental blood flow -> reductions fetal HR-> fetus stressed -> rising cortisol by fetus -> fall in placental progesterone relative to oestrogen -> Increase prostaglandin and oxytocin sensitivity

(Prostaglandins induce labour when given medically)

Question 11

How long is the second stage of labour?

Answer 11

Normally up to 1hr multiparous and up to 2 in primigravida

Question 12

What are the steps involved in the second stage of labour?

Answer 12

1. Descended head flexes as it meets pelvic floor
2. Internal rotation
3. Flexed head descends to vulva, stretching vagina and perineum
4. Head delivered (crowning) and rotates back to region position
5. Shoulders rotate followed by head, fetus delivered

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Question 13

What occurs in the third stage of labour?

Answer 13

Powerful uterine contraction separates the placenta - positioning it into upper part of vagina or lower uterine segment and compresses blood vessels and reduces bleeding (can be enhanced by oxytocic drug)

Placenta and membranes expelled (normally within 10mins)

Question 14

How do we measure the condition of the neonate?

Answer 14

APGAR score - soon after delivery and 5mins later

1-10 higher= healthier

Question 15

Which clinical elements of labour are classified as the power?

Answer 15

Delivery of the fetus dependent contraction myometrium, contraction and retraction of multidirectional smooth muscles fibres, contractions can be assessed in terms of frequency/ amplitude/ duration

Question 16

Which clinical elements of labour are classified as the passage?

Answer 16

Formed by bony pelvis and soft tissues, pelvic inlet is shorter in anterio posterior plane

Between pelvic inlet and outlet is the mid-cavity circular

Pelvic outlet narrowest mediolaterally

Fetus flexes, extends, rotates

Resistance of soft tissue can slow labour

Question 17

Which clinical elements of labour are classified as the passenger?

Answer 17

Size and presentation of fetus is critical, orientation of head when entering pelvis is variable, moulding of fetal cranium May occur since cranial sutures not yet fused

Problems: fetus too big, fetus presentation not good