(10.1) Birth

Question 1

State the aim of each stage of birth giving.

Answer 1

• First: Creation of birth canal
• Second: Expulsion of foetus
• Third: Expulsion of placenta

Question 2

How is the birth canal enlarged during pregnancy?

Answer 2

• Oestrogen > Progesterone at end of pregnancy -> Endometrium produces Prostaglandin
• Prostaglandin -> + [Ca2+]i smooth muscle cells -> + force of Myometrium contraction
• Prostaglandin -> Ripening -> + Cervix stretchiness
• Pacemakers -> contraction -> Myometrium pushes foetal head -> Cervix stretches
• Stretched Cervix -> Ferguson feedback -> + Hypothalamus -> + Posterior Pituitary -> + Oxytonin
• Oxytonin -> - Action Potential Threshold -> + frequency of Myometrium contraction

Question 3

What type of molecule is Prostaglandin? Where is it produced? What stimulates its production?

Answer 3

• Biological active lipid
• Endometrium
• Oestrogen > Progesterone at late pregnancy

Question 4

Which types of Prostaglandin play major roles at aiding labouring? What are their main actions?

Answer 4

• PG E2 & F2x
• • [Ca2+]i smooth muscle cells -> + force of Myometrium contraction
• Ripening of Cervix -> + stretchiness

Question 5

How is the production of Oxytonin stimulated? Where is it produced?

Answer 5

• Ferguson Reflex: +ve feedback from stretched cervix -> Hypothalamus
• Produced by Posterior Pituitary Gland

Question 6

How is the Amniotic Fluid released at birth?

Answer 6

Stretched Cervix -> raptures Fetal Membrane -> Release

Question 7

What factors determine the maximum size of birth canal except from the expansion of soft tissues.

Answer 7

• Softening of ligaments by Progesterone
• Pelvic Inlet: 10.5cm, antero-postrior shorter
• Pelvic Cavity: 12cm, round
• Pelvic Outlet: 11cm, medial-lateral shorter

Question 8

Briefly describe the common positional changes of the foetus during labouring.

Answer 8

1. Flexion of head ~9.5cm & Rotation of head
2. Head stretches vagina & perineum (risk of tearing)
3. Delivery of head & Rotation of shoulder
4. Delivery of shoulder & the rest follows

Question 9

Describe the contraction of Uterus, how it aids the expulsion of foetus?

Answer 9

Brachystasis = relaxation less than contraction -> shortening of smooth muscle fibres -> pushes presenting part of foetus down to cervix

Question 10

Suggest causes of failure in labouring.

Answer 10

• Inadequate contraction of myometrium
• Inadequate birth canal e.g. bony pelvis / rigid peritoneum
• Foetus too big / Fetal breech position

Question 11

How might you give the mother to help her uterus to contract?

Answer 11

Prostaglandin & Oxytotic drugs

Question 12

How is the Placenta expelled?

Answer 12

• Contraction of uterine -> shortened fibres -> expels

Question 13

Expulsion of Placenta may cause severe haemorrhage, how is it prevented? What is the normal amount of blood flow to Placenta?

Answer 13

• Persist contraction of Uterus 5-15 mins after birth -> compress blood vessels
• 500-800ml /min (10-15% of cardiac output)

Question 14

What is the first line treatment of postpartum haemorrhage?

Answer 14

Oxytotic drugs -> + uterine contraction -> compress blood vessels

Question 15

How can you monitor the state of the foetus during labouring?

Answer 15

Fetal scalp electrode

Question 16

What is C section? Briefly describe how it is performed. In what situation is it normally performed?

Answer 16

• Cesarean Section
• Suprapubic Incision at Linia alba & Anterior Rectus Sheath -> retracted Rectus muscles laterally
• Placenta Previa: implantaion at lower uterus, over cervix

Question 17

What is the full name of C section? State two forms of operative delivery other than C section.

Answer 17

• Cesarean Section
• Forceps delivery
• Vacuum Extraction

Question 18

What term is used to describe birth that occurs at

Answer 18

Spontaneous abortion = not ture abortion, but unlikely that the foetus would survive

Question 19

When is the foetus normally born? What is it called if born before that?

Answer 19

• 37-42 weeks

- Pre-term

Question 20

Which hormone helps to increase the size of pelvic inlet before earlier in pregnancy and how?

Answer 20

• Progesterone

- Softens Sacrotuberous & Sacrospinous ligaments

Question 21

Describe the contraction of myometrium before labouring, in early and late pregnancy. What are their purposes?

Answer 21

• Early: frequent, less forceful (not noticeable)
• Late: less frequent, forceful (may cause pain, aka Braxton Hicks)
• Practice contraction to help with cervical effacement etc

Question 22

Which hormone inhibits the uterine to contract?

Answer 22

Progesterone

Question 23

Why do you get Lordosis towards end of pregnancy?

Answer 23

• Foetal weight

- Relaxins + other hormones -> stretchy ligaments including vertebral ligaments

Question 24

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

Answer 24

Foetal frontanelles

Question 25

What is Epidural anaesthesia?

Answer 25

• Insertion from the back

- Blocking T9-S4

Question 26

What are the boundaries of the Pelvic Inlet?

Answer 26

• Pubic symphysis & Superior pubic rami anteriorly
• Ilio-pectineal line laterally
• Sacral promontory posteriorly