Obstetrics: Labour Onset and Fetal Positioning

Onset Of Labour

• The onset of labour is a complex and not fully understood process
• Hormonal changes, particularly the increase in oxytocin and prostaglandins, play a key role in initiating labour
• Other factors contributing to the onset of labour include:
  • Fetal movement and pressure on the cervix
  • Stretching of the uterus and pelvic floor
  • Changes in the cervix and lower uterine segment

Fetal Positioning

• Fetal positioning refers to the way the baby is positioned in the uterus during labour
• Optimal fetal positioning is important for a smooth and efficient labour
• Factors influencing fetal positioning include:
  • Maternal posture and movement
  • Uterine shape and size
  • Fetal size and shape
  • Placental location

Contraction Patterns

• Contraction patterns refer to the frequency, duration, and intensity of uterine contractions during labour
• Normal contraction patterns include:
  • Contractions every 5-30 minutes, lasting 30-70 seconds, and increasing in intensity
  • Contractions becoming more frequent, longer, and stronger as labour progresses
• Abnormal contraction patterns include:
  • Contractions that are too frequent, too long, or too strong
  • Contractions that are irregular or unpredictable

Cervical Dilation

• Cervical dilation refers to the opening of the cervix during labour
• The cervix dilates from 0-10 cm, with 10 cm being fully dilated
• Cervical dilation is typically measured in centimeters, with the following milestones:
  • 3-4 cm: active labour begins
  • 7-8 cm: transition phase begins
  • 10 cm: full dilation, ready for pushing

Event 1st Stage of Labour

• The first stage of labour is the longest stage, lasting from the onset of labour to full cervical dilation
• The first stage of labour is divided into two phases:
  • Early labour (0-3 cm dilation): contractions are mild and irregular
  • Active labour (4-7 cm dilation): contractions are stronger and more frequent
• The first stage of labour can last anywhere from 6-24 hours, with an average duration of 8-12 hours

Contraction and Retraction

• Contractions refer to the periodic tightening of the uterine muscle during labour
• Retraction refers to the process of the uterine muscle shortening and thickening during contractions
• The combination of contractions and retraction helps to:
  • Move the fetus down the birth canal
  • Dilate the cervix
  • Prepare the uterus for the second stage of labour (pushing)

Onset of Labour

• Hormonal changes, including increased oxytocin and prostaglandins, initiate labour
• Fetal movement and pressure on the cervix contribute to the onset of labour
• Stretching of the uterus and pelvic floor, and changes in the cervix and lower uterine segment, also play a role

Fetal Positioning

• Fetal positioning is crucial for a smooth and efficient labour
• Maternal posture and movement, uterine shape and size, fetal size and shape, and placental location influence fetal positioning

Contraction Patterns

• Normal contractions occur every 5-30 minutes, last 30-70 seconds, and increase in intensity as labour progresses
• Abnormal contraction patterns include contractions that are too frequent, too long, or too strong, or irregular and unpredictable

Cervical Dilation

• Cervical dilation measures the opening of the cervix, from 0-10 cm
• 3-4 cm dilation marks the beginning of active labour
• 7-8 cm dilation marks the transition phase
• 10 cm dilation indicates full dilation, ready for pushing

First Stage of Labour

• The first stage of labour lasts from the onset of labour to full cervical dilation
• Early labour (0-3 cm dilation) has mild and irregular contractions
• Active labour (4-7 cm dilation) has stronger and more frequent contractions
• The first stage of labour typically lasts 8-12 hours, but can range from 6-24 hours

Contraction and Retraction

• Contractions are periodic tightenings of the uterine muscle during labour
• Retraction is the shortening and thickening of the uterine muscle during contractions
• Contractions and retraction help move the fetus down the birth canal, dilate the cervix, and prepare the uterus for the second stage of labour (pushing)

Event of 1st Stage of Labour

• Begins with onset of regular uterine contractions and ends when cervix is fully dilated (usually 10cm)
• Divided into two phases: Early labour (latent phase) and Active labour (active phase)

Phases of 1st Stage of Labour

• Early Labour (Latent Phase)
  • Contractions become more frequent and intense
  • Cervix dilates to 3-4cm
• Active Labour (Active Phase)
  • Cervix dilates from 4-10cm
  • Contractions become stronger and more frequent

Contractions

• Characteristics
  • Regular, rhythmic, and increasing in intensity
  • Lasting around 30-70 seconds, with a frequency of 3-5 per 10 minutes
  • Becoming more frequent and intense as labour progresses
• Types of Contractions
  • Braxton Hicks Contractions
    • Irregular, mild, and practice contractions
    • Prepare the uterus for labour
  • True Labour Contractions
    • Regular, intense, and productive contractions
    • Help dilate the cervix

Retraction

• Definition
  • Process by which the uterine muscle shortens and thickens
  • Pulls the cervix upwards and outwards
• Purpose
  • Helps dilate the cervix and push the baby down the birth canal
• Effects on the Cervix
  • Causes the cervix to thin and dilate
  • Helps move the cervix out of the way, allowing the baby to descend
• Relationship with Contractions
  • Occurs in response to contractions
  • Helps progress labour