Week 10 - Birth

Question 1

When does the uterus first become palpable?

Answer 1

At around 12 weeks

Question 2

When does the uterus reach the level of the umbilicus?

Answer 2

At about 20 weeks of gestaton

Question 3

When does the uterus reach the level of the xiphisternum?

Answer 3

At about 36 weeks of gestation

Question 4

What is classified as premature or pre-term labour?

Answer 4

Expulsion of the products of conception before 37 weeks of gestation

Question 5

What is the girth at the umbilicus until 24 weeks gestation? How much does it increase until term?

Answer 5

Remains at about 60 cm average

Should increase by about 2.5 cm per week until term, when it should be 100 cm

Question 6

What is the approximate diameter of presentation when the baby lies longitudinally in a cephalic presentation, well-flexed so that its vertex presents to the pelvic inlet?

Answer 6

9.5 cm

Question 7

What diameter does the birth canal need to have approximately to allow the fetus to pass through?

Answer 7

10 cm

Question 8

What is the true diameter of the pelvic inlet?

Answer 8

Normally about 11 cm

Question 9

What changes must occur in the cervix to create a birth canal?

Answer 9

The cervix must dilate and be retracted anteriorly

Question 10

What structural changes does cervical ripening involve?

Answer 10

1. Marked reduction in collagen and marked increase in glycosaminoglycans which reduce the aggregation of collagen fibres
2. Keratin sulphate increases at the expense of dermatan sulphate
3. In consequence, collagen bundles loosen
4. There is also influx of inflammatory cells and increase in nitric oxide output
5. All of these changes are triggered by prostaglandins - namely E2 and F2x

Question 11

Identify the oestrogen mediated changes in the cervix and pelvis occurring in advancing pregnancy that will facilitate birth.

Answer 11

1. Cervical softening

2. Relaxation of pelvic ligaments

Question 12

Where is the pelvic inlet shorter?

Answer 12

In the anterior-posterior plane (obstetric conjugate = 10.5 cm)

Question 13

Where is the pelvic outlet narrowest?

Answer 13

Mediolaterally (11 cm)

Question 14

What may failure of progression in labour occur because of?

Answer 14

1. Inadequate power - insufficient uterine contractions
2. Inadequate passage - abnormal bony pelvis, rigid perineum
3. Abnormalities of the passenger - fetus too big, fetal presentation

Question 15

What is progress in labour plotted graphically on?

Answer 15

A partogram

Question 16

What is the mechanism of action for prostaglandins and oxytocin in inducing labour?

Answer 16

1. Prostaglandins: enhance release of calcium from intracellular stores
2. Oxytocin: lower the threshold for triggering action potentials

Question 17

What is a major producer of prostaglandins?

Answer 17

The endometrium

Question 18

What controls the synthesis of prostaglandins?

Answer 18

Prostaglandin release is controlled by the release of phospholipase from liposomes - the major factor influencing this in the endometrium is the oestrogen/progesterone ratio

Question 19

What increases prostaglandin synthesis?

Answer 19

1. A rise in oestrogen and a fall in progesterone

2. The action of oxytocin