Oxford Handbook of Midwifery (50 page)

Treatment

Maintenance dialysis

Fertility generally decreases in women with end-stage renal disease but improved treatment can lead to a health improvement enough to restore fertility. There is however a low fetal survival rate, prematurity is a major problem and polyhydramnios is common.

Renal transplant recipients

There is a greater chance of a successful pregnancy with a gap of 2 years between transplant and conception. The incidence of preterm delivery is high as is IUGR. Fetal prognosis depends on how well the allograft con- tinues to function and hypertension, proteinuria, and renal function must be closely monitored.

Recommended reading

Hnat M, Sibai B (2008). Renal disease and pregnancy.
Global Library of Women’s Medicine
(ISSN: 1756-2228) 2008; DOI 10.3843/GLOWM.10157.

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Part 2
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Normal labour

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Normal labour: first stage
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Physiology of the first stage of labour
200

Diagnosis of onset of labour
204
Support for women in labour
208
High- and low-risk labour
210

Principles of care for low-risk women
211
Principles of care in the first stage of labour
212
Home birth
214

Hospital birth
218

Water birth
220

Mobility and positioning in labour
224

Nutrition in labour
226
Assessing progress of labour
228
Abdominal examination
230

Vaginal examination
232

The partogram
234

Cardiotocograph monitoring
236

Monitoring fetal well-being
238

Chapter 00

Chapter 11

199

CHAPTER 11
Normal labour: first stage

200‌‌

Physiology of the first stage of labour

Definition of labour

The physiological process by which the fetus, placenta, and membranes are expelled through the birth canal. The first stage of labour is from the onset of regular uterine contractions until full dilatation of the cervix.

Normal labour

• Is spontaneous, occurs between 37 and 42 weeks’ gestation.
  
• Culminates in the normal birth of a live, healthy infant.
  
• Is completed within 24h and there are no maternal complications.
  

  The two main physiological changes that take place in the first stage are effacement and dilatation of the cervical os. These are initiated by the action of various hormones and prostaglandins, and the contraction and retraction of the uterine muscle. The mechanism by which labour is initiated is still not fully understood. Some theories suggest that it involves a very complex interaction between the mother, the fetus, and their environment.
  

  Initiation of labour
  

  Increasing levels of prostaglandins, oxytocin, and progesterone are thought to contribute to the initiation of the onset of labour. The levels then rise progressively, reaching highest levels at delivery of the head and after placental separation.
  

  The myometrium
  

  Individual cells within the myometrium are able to depolarize their cell membranes allowing the movement of ions, primarily calcium, which together with ATPase initiates the contraction of myosin fibres within the cell. The cells are able to communicate their activity via gap junctions. If this process occurs together, this results in a harmonized contraction, which can spread across the uterus. At term, muscle fibres are present in compact bundles, reducing the gap size, therefore the number of gap junctions increases and the potential to stimulate contractility is increased.
  

  The cervix
  

  The cervix consists of collagen fibres alternating with circular and longitu- dinal muscle fibres. Normally the cervix is firm and resistant to downward
  

  activity from the uterus and its contents. Towards term the percentage of water in the collagen fibres increases which decreases stability and there- fore results in a softer, more compliant cervix.
  

  Hormonal influences
  

  Oestrogen enhances myometrial activity by increasing oxytocin and prostaglandin receptors, in turn this assists with the formation of gap junctions.
  

  Prostaglandins are produced in the placenta, membranes, and decidua. PGE and PGF2a facilitate the production of calcium ions which increases their availability for binding to the myosin receptors. This enhances contractile action and results in harmonized contractions. The presence
  

  PHYSIOLOGY OF THE FIRST STAGE OF LABOUR
  

  201
  

  of prostaglandins in the cervix encourages the production of enzymes to reduce the amount of collagen, this leads to cervical ripening.
  

  Oxytocin acts as a hormone and neurotransmitter and is produced by the hypothalamus, it is a powerful uterine tonic. An increase in oxytocin receptors, due to the action of oestrogen, dramatically increases uterine sensitivity to oxytocin at term. This facilitates the onset and maintenance of contractions by depolarization and stimulating the production of prostaglandins. Animal studies suggest that relaxin is instrumental in stimulating oxytocin-synthesizing neurons in the hypothalamus just before the onset of labour.
  

  Physiological changes in the first stage
  

in obstructed labour, when a transverse ridge across the abdomen forms—known as Bandl’s ring—indicates imminent rupture of the uterus.