Labour

Question 1

Parturition

Answer 1

• Progessive increase in intensity and frequency of uterine contractions leading to dilatation of the cervix, descent of the fetus, and ultimately explusion of the baby, placenta and membranes.
  
  • Consists of progessive cervical effacement dilation from uterine contractions occuring at least every 5mins and lasting 30-60seconds.

Question 2

Pelvic Shapes

Answer 2

• The female pelvis can be classified into different shapes. This is clinically relavent since each shape has a different point of largest diameter. it will effect how the fetal head will engage.

1. Gynecoid - this is the classic female pelvis found in ~50% of women. It is characterized by a cylindrical shape that is spacious throughout. Fetal head will generally rotate into the occipitoanterior position.
2. Android - this is the classic male pelvis, found in <30% of women. Characterized by a triangular inlet. In this type, there is limited space at the inlet with pregressively less space as you move down. Fetal head goes into occipitoposterior position. Arrest of descent is common at midpelvis.
3. Anthropoid - Found in ~20% of women. Characterized by an oval inlet (longest along the vertical). Fetal head engages in the occipitoposterior position, because there is more room in the posterior pelvis.
4. Platypelloid - Found in <3% of women. Characterized by an oval shaped inlet (longest along the horizontal). Fetal head engages in the transverse diameter.

Question 3

Engagement

Answer 3

• When widest diameter of fetus has passed through the pelvic inlet.

Question 4

What physiologic preparatory events occur before labour?

Answer 4

• Lightening - A flattening of the upper abdomen and increase in size of lower abdomen as the fetal head moves into the brim of the pelvis. This occurs 2 or more weeks before labour in primigravid women and occurs in early labour in multigravida women.
• False labour - in the last 4-8 weeks of pregnancy the uterys has irregular, painless, contractions. They can be rhythmic and of mild intensity. In the last month these contractions may occur more frequently and with greater intensity (Braxton Hicks Contractions). This is considered false labour because there is no cervical dilation or effacement.
• Cervical effacement - before labour the cervic softens due to increase water content and collagen lysis. Cervix shortens as it is progressively taken up into the lower segment of the uterus. With effacement the mucous plug within the cervix may be released (bloody show).

Question 5

Stage 1 of labour

Answer 5

• Stage 1 (0-10cm dilatation) consists of 2 phases

1. Latent phase (dilatation to 3-4cm) - cervical effacement and rapid cervical dilation. Contractions needs to get at least 25mmHg to start dilating cervix.
2. Active phase - Starts when cervix is 4cm dilated in presence of regulary occuring uterine contractions. It is characterized by more rapid cerival dilation.

• Length of first stage may be prolonged if this is the first child, mother is older, mother has high BMI, or patient used an epidural.
• Lasts ~12-13hrs for first child and ~7-8hrs for second child

Question 6

“Good contractions”

Answer 6

• In the 1st stage contractions needs to become coordinated, regular, more intense, and more frequent.
• Good contractions in active phase= every 2-3mins, lasting 45-60seconds, having intensity of 60-70mmHG.
• The uterine muscle is an involuntary smooth muscle, arranged multi-directionally. With contractions, the upper segment thickens and the lower segments thins, pushing the fetus downwards and forcing the cervix open.

Question 7

Second stage of labour

Answer 7

• At start of second stage the mother has an urge to bear down with each contraction. Abdominal pressure and uterine contractile force combines to expel the fetus.
• In this stage, fetal descent must be closely monitored. Fetus does throught the following motions.
  
  • Descent, flexion, internal rotation, extension, external rotation, expulstion
• This stage usually take 30mins-3hrs in primigravida women and 5-30mins in multigravida.

Question 8

Mechanism of labour (6 movements of the fetus)

Answer 8

1. Descent - fetus moves down due to force of uterine contraction, maternal bearing-down efforts, and gravity if patient is upright.
2. Flexion - partial flexion is already present before labour. During descent resistance from cervix and pelvic causes further flexion of cervixal spine, with baby’s chin approaching its chest. The purpose of this is to change the presenting head diameter to a smaller one.
3. Internal rotation - In occipitoanterior position, fetal head turns so that the back of the head faces the symphysis pubis. Internal rotation occurs as the fetal head meets the muscular sling of the pelvic floor.
4. Extension - flexed head in occipitoanterior position continues descent. Since vaginal outlet is directed upward & forward, extension is needed for head to pass through. As head continues to descend there is a bulging of the perineum followed by crowing ( when largest diameter of the head is encircled by vulvar ring).
5. External rotation - In both OA and OP position, the delivered head returns to original position at time of engagement to align with fetal back and shoulders.
6. Expulsion - After external rotation of the head, the anterior shoulder delivers under the symphysis pubis, followed by the posterior shoulder over the perineal body, and the body of the child.

Question 9

Third stage of labour

Answer 9

• Delivery of the placenta.
• Immediately following delivery of the baby, the cervix and vagina should be thoroughly inspected for lacerations and surgical reparis should be preformed if needed.
• Delivery of the placenta usually occurs within 2-10 mins of the end of the second stage. (Should occur within 30mins max)

Question 10

Signs of Placental Separation

Answer 10

1. Fresh show of blood from vagina
2. Umbilical cord lengthens outside of vagina
3. Fundus of uterus rises up
4. Uteus becomes firm and globular

• Only once these signs occur should you attempt traction on the cord (pull gently with counterpressure between symphysis and fundus to prevent uterine descent).
• Should administer 20U of oxytocin after the placenta has been delivered. Oxycotin is a uterotonic agent that causes uterine contractions and prevents postpartum hemorrhage.

Question 11

Fourth stage of labour

Answer 11

• Hour following delivery.
• Requires close observation of the patient.
  
  • Monitor BP, Pulse, and Uterine blood loss

Question 12

Induction and augmentation of labour

Answer 12

• Induction - process where labour is initiated by artifical means
  
  • Induction of labour involved 2 processes
    
    • Mechanism to promote cervical ripening (effacement and softening) - local application of postaglandins, intrauterine placement of catheters, use of osmotic dilators.
    • Initiation of uterine contractions - oxytocin
• Augmentation - artificial stimlation of labour that has begun spontaneously

Question 13

Indications for induction

Answer 13

• Only indicated when continuation of pregnanacy represents significant risk to fetus or mother. Inducation may be indicated at term in the case of premature rupture of the membranes.

Question 14

Continuous Electronic Fetal Monitoring

Answer 14

• Electronic fetal monitoring allows for the continuous reporting of fetal heart rate (FHR) & uterine contractions by means of a monitor that prints results on a 2-channel strip chart recorder.
• Can be obtained using an external transducer or through internal monitoring -> internal monitoring gives more precise measurements.

Question 15

Baselines assessment FHR

Answer 15

• Assessment of FHR depends on the evalutation of the baseline pattern and periodic changes related to uterine contractions. Can be divided into short-term or long-term variability.
  
  • Short-term - interval between either successive fetal ECG signals or mechanical events of teh cardiac cycle. Normally flutuates between 5 & 25 BPM. Variability of <5BPM = severe fetal distress.
  • Long-term - flutuations in frequency and amplitudes of change in the baselines rate. Normally it is 3-10 cycles per minute.
• Normal FHR during labour = 110-160 BPM with variability of 5-25BPM

Question 16

Periodic fetal heart rate changes

Answer 16

• Changes in baseline FHR related to uterine contractions

1. No change - FHR has same characteristic as baseline
2. Acceleration - FHR increases in reponse to uterine contractions (normal response)
3. Deceleration - FHR decreases in response to uterine contractions. Decelerations may be early, late, variable, or mixed. All except early are abnormal.
   
   • Early - seen with engagement of the fetal head. Pressure on fetal head leads to a vagal response in the fetus.
   • Late - severe repetitive late decelerations are usually indicative of fetal metabolic acidosis
   • Mixed difficult to define

Question 17

Vaginal Bleeding after 20 weeks gestation

Answer 17

• Placenta Previa - Placenta is lying unusually low in uterus, next to or covering the cervix. Digital exam of the cervix should be avoided until this is rules out. Must do sonographic examination.
• Abruptio Placenta - premature separation of normally implanted placenta prior tp delivery. Risk factors = trauma, prior placental abruption, smoking, cocaine use, HTN, preterm premature rupture of membranes.
  
  • Patients typically present with vaginal bleeding, uterine tenderness, and uterine contractions.
  • Only 2% can be detected on US
• Vasa Previa - fetal blood vessels are present in membranes covering internal cervical OS
• Bloody show - small amount of blood with mucus discharge that may precede onset of labour.

Question 18

Forceps Delivery

Answer 18

• Forceps are instruments designed to provide traction and rotation of the fetal head when expulsive forces of mother are insifficient to complete delivery.
• Indications:
  
  • Prolonged second stage of labour.
  • Suspicion of immediate or pending fetal compromise
  • To stabilize head during breech delivery
  • To shorten 2nd stage for maternal benefit.
• In order to use forceps the cervix must be fully dilated, membranes ruptured, and fetal head engaged into the pelvis.

Question 19

Vacuum extraction delivery

Answer 19

• Vacuum extraction - instrument that uses a suction cup that is applied to the fetal head. This is easier to use than forceps.
• Flexion of the fetal head must be maintained to provide smallest dimater to the maternal pelvic.
• Indications are the same as forceps. However, it is contraindciated in preterm delivery, because fetal head and scalp is more prone to injury from suction cup. It can also never be used for fetuses presenting by face or breech.

Question 20

Cesarean Delivery

Answer 20

• Delivery through an incision in the maternal abdomen and uterus.
• Indications:
  
  • Dystocia
  • Repeat C-section
  • Breech presentation
  • Fetal distress
  • Previous full-thickness, non-transverse incision through myometrium
  • Placenta Previa

Question 21

Dystocia

Answer 21

• Dysfunctional labour. It characterizes labour that does not progress normally. Problem may be cuased by
  
  • Abnormalities of power - ineffective uterine expulsive force
  • Abnormalities of passenger - abnormal fetal position (not in OA position), or anatomic defects
    
    • Macrosomia - fetus ≥ 4500g has increased risk of shoulder dystocia, genital trauma, and increase in C-section.
    • Shoulder dystocia - difficultly in delivering the shoulder. Occurs from impaction of the shoulder on the pubic symphysis anteriorly or the sacral promontory posteriorly.
  • Abnormalities of passage - maternal bony pelvic contracutres resulting in mechanical interference with the passage of the fetus through the birth canal.

Question 22

What generally indicates the start of labour?

Answer 22

1. Onset of regular, more intense, and more frequenct contractions (80%)
2. Rupture of membranes (20%)
3. Bloody show/ passage of mucus plug (common for mucus plug to break off before labour)