What is labor?

Labor is the chain of physiologic events that leads to the

delivery of the fetus to the outside world.

Labour may occur:

•Preterm (or prematuere) (< 37 weeks, 259 days)

•Term (37 weeks to <42 weeks) or

•post-term (>42 weeks 294 days).

It can also be spontaneous or induced.

Successful labor depends on the interaction of three variables:

The force (uterine contractions). The passenger (the fetus).The passage (the birth canal).

Uterine contractions (The Force)

In the first stage:Uterine contractions result in cervical dilatation. In the second stage:It drives the fetus downwards through the birth canal. In the third stage: It is responsible for separation, and expulsion of the placenta and prevention of atonic postpartum hemorrhage.

The difference between the histology and physiology of the upper and lower uterine segments is responsible for completion of successful labor.

The upper and lower uterine segments

The upper and lower uterine segments

The upper and lower uterine segments

The upper segment is rich in muscle fibers that actively contract and retract

the lower segment is rich in fibrous tissue therefore it does not contract but is rather passively pulled up by the actively contracting upper segment

Fig. 8-1: “A” at onset of active stage of labor the lower segment is this and the cervix is effaced (thin and short). “B-C” During the active phase of labor with contraction and retraction the upper segment fibers becomes shorter, thicker the results are dilatation of the cervix and descent of the fetus.

The Diagram shows the process of cervical ripening and dilatation. Contractions and retractions of the upper segment leads to stretching, thinning of the lower segment and cervical dilatation.

The Fetus (The Passenger)In normal labor as the fetus descends through the birth canal it undergoes

series of movements (Cardinal Movements). The aim of those movements is to adapt the fetus smallest head diameters

to pass through the largest pelvic diameters as it passes each strata of the pelvis i.e. inlet, cavity, and outlet.Increased Flexion and Engagement: Internal rotation:Extension: External rotation (restitution): Delivery of the shoulders

Fig. 8-4: Shows the diameters of the fetal head at different levels of flexion. In occipito-anterior position with full flexion the engaging diameter is the suboccipitobregmatic diameter (9.5 cm) compared to occipito posterior presentation with deflexed head the engaging diameter is Occipito-frontal diameter (11.5 cm).

The Diagram shows the use of the role of fifth in assessment of descent of the fetal head abdominally;If the five fifth of the head is felt abdominally means that the whole head is still above the pelvic brim.The head is considered engaged if less than 3/5 of the head is felt above the abdomen.

The Role of Fifth in assessment of the Fetal Head Engagement

Level of head engagement

Assessment of the Fetal Head Engagement by Clinical Vaginal Examination

The zero station is the level of the pelvic ischial spines.If the leading presenting part reaches below the ischial spines (0+1) the head is considered engaged.

Fig. 8-5: ”A” “gynecoid pelvis” a rounded oval pelvis with well-rounded anterior and posterior segments ”B” Android pelvis showing wedge-shaped inlet and narrow anterior segment

The Pelvis (Passage)

The term passage refers to the bony pelvis and the soft tissues of the birth canal (i.e., cervix, vagina, and pelvic floor musculature), they undergo important changes throughout pregnancy and during labor.

– At term the pelvic ligaments under the influence of the hormone “Elastine” already became soft and lax. This allows further stretching and increase in the absolute pelvic diameters during the descent of the fetus (sometimes known as “pelvic give”).

– The soft tissues of the birth canal gradually get softer and more stretchable as pregnancy approaches term. The cervix undergoes process of “ripening”. A “ripe” cervix at term facilitate stretching and dilatation in response to uterine contractions.

Third stage

Time from expulsion of the fetus to expulsion of the placenta

The third stage

•Signs of separation of the placenta:

•Active management of the third stage:

•Duration of the third stage: Normally the placenta is delivered within few minutes after delivery of the fetus. In about 2-3% of cases, the placenta may remain undelivered for more than 30 minutes. If by then the placenta is not easily delivered the condition is diagnosed as “retained placenta” which require special management (Chapter 18 Postpartum Complications)

(1) A gush of blood.

(2) Lengthening of the umbilical cord.

(3) the uterus becomes firm and globular

Signs of separation of the placenta:

Fig. 8-7: Placenta before and after separation with retropalcental clot. Note the 3 signs of placental separation in the diagram on the right.

The Fourth Stage of LabourDefinition:

Is the few hours after complete delivery of the placenta. During this hours the mother should remain under close observation for immediate complications such as uterine atony and hemorrhage.

Management:

Normal Labour and it Management

Definition

Diagnosis

Stages and Phases of Normal Labour

Management of normal labour: (see lecture on normal labor)

Definition of Normal labor

The presence of regular uterine contractions that cause:

- Progressive dilation and effacement of the cervix and.

- Fetal descent

Labour could be spontaneous or Induced

Term or Preterm

Diagnosis of Labour

Symptoms:

- Regular Painful Contractions, Increase in Frequency and Intensity.

- Bloody Show.

Signs:

Cervical Changes :effacement and dilatation

Normal Labour and it Management

Definition Diagnosis Stages and Phases of Normal Labour Management of normal labour:

• Second stage: Time from complete cervical dilatation to expulsion of the fetus

• Third stage: Time from expulsion of the fetus to expulsion of the placenta

latent

Active

Acceleration Phase

Maximum slope

Deceleration phase

• First stage:

Time from the onset of labor until complete cervical dilatation

• Fourth Stage

First StageFrom onset of labour to full dilatation of the cervix

• Latent Phase: Short, Mild, Uterine Contractions

From onset of labour until the cervix is about 3 cm dilated and fully effaced

• Mean Length: - 9 (+ 6) h in primigravida- 5 (+ 4) h in multigravida

• Active Phase:

Dilatation of cervix from 3 cm • Mean Length:

- 5 (+ 3.5) h in primigravida- 2 (+ 1.5) h in multigravida

Duration of Normal Labour

• Varies Between Nulliparous And Parous Parturients.

• The Average Duration Of Active Labor (Onset Defined As 3 Cm Dilation) In Nulliparous:6.4 hours

Parous: 4.6 hours

THE SECOND STAGEFrom Full Cervical Dilatation Till Delivery of the

Baby

• Phases:- Propulsive Phase: From full Dilatation till the presenting part reach the pelvic floor- Expulsive Phase: From then until the birth of the baby (the mother wishes to bear down and the perineum is distended)

• The Duration: varies in nulliparous and multiparous women is 50 and 20 minutes, respectively.

• Factors may affect its duration: Epidural analgesia, parity, maternal size, birth weight, and station at complete dilation.

Fig. 8-6: Shows Phases of labor. The first stage composed of the Latent and Active phase. The main changes in the latent phase is cervical effacement and slight degree of dilatation. The Active phase is the phase of rapid cervical dilatation.

Parameters Nulliparous Multiparous

Duration of labor Mean Mean +2SD Mean Mean +2SD

Total duration of labor (hours) 10.7 25 6.2 h 19.5

First Stage (hours) 9.7 24 8.0 18.0

Second Stage (minutes) 33.0 m 117.0 m 8.5 m 46.5 m

Third stage (minutes) 5 m 30 m 5 m 30 m

Rate of cervical dilatation Mean Mean -2SD Mean Mean -2SD

Rate of cervical dilatation Cm /hour 3.0 1.2 cm/h 5.7 1.5

Table 8-1: Mean normal duration of labor and the two standard deviation from the mean. Currently the duration of the 2nd stage is based on parity and the presence of regional anesthesia with no intervention as long as there is progress and the fetal condition is stable.

The pattern and duration of normal labor The maximum (slowest) duration of each stage is defined as two standard deviations

below the mean.

Labor is considered abnormally prolonged if it exceeds the normal upper limits of the normal range.