Normal Labor and Delivery

Dr Narine Singh MBBS ,MSc

Normal Labor

In order to maximize the patient chance of a vaginal delivery ,it is important to understand the basics of labor

• Stages of labor

• Mechanics of labor

• Cardinal movements of labor

• delivery

Normal Labor and Delivery

• Definition of labor

• Factors influencing progress of labor

• Diagnosis of labor

• Stages of labor

• Mechanism of labor

• Management of labor

What is Labor

Definition

Labor is a physiologic process during which the products of conception (i.e. fetus ,membranes ,umbilical cord and placenta) are expelled from the uterus

More specifically, Labor requires the onset of regular ,effective contractions that lead to progressive cervical effacement and dilatation of the cervix accompanied by descent of the presenting part

Definition

Labour is

regular ,frequent uterine contraction

+

cervical change

(dilatation and effacement)

Labor can occur at

• Preterm labor --- prior to 37 weeks

• Term --- 37-42 weeks

• Post term --- after 42 weeks

• Postdates --- after 40 weeks

Normal Labour

Labour is normal when it is

• Spontaneous in onset

• At term (37 completed weeks-42 weeks)

• Single fetus

• Vertex presentation

• Within a reasonable time(not less than 3 hrsor more than 18 hrs.)

• Without complication to the mother or the fetus

Normal Labour

• Any deviation from this definition is abnormal

• In late pregnant ,strong contraction can sometimes be palpated that do not produce cervical dilatation ,even when the cervix is normal and these do not constitute true labour (Braxton – Hick)

• Cervical dilatation in the absence of uterine contraction suggest cervical insuffiiciency,whereas uterine contraction without cervical change does not meet the definition of labour

• Delivery refers to the complete expulsion of the products of conception

Normal labor

Braxton –Hick uterine contraction NOT associated with cervical change

• Shorter in duration

• Less intense

• Over lower abdomen and groin

• Resolves with ambulation

Onset of labour

• Based on the naegel’s formula ,labour starts approximately as follow

• In the expected date of delivery (EDD) in 40%of cases

• One week on either side in 50% of cases

• Two weeks earlier and one week later in 80%of cases

• At 42 weeks in 10%of cases

• At 43 weeks plus in 4% of cases

Causes of onset of labour

The actual cause for the onset of labor is not exactly known ,but several theories have been postulated but none of them is completely proven

• Hormonal factors

• Mechanical factors

Onset of labour

Hormonal factors

• Estrogen theory

• Progesterone withdrawal theory

• Prostaglandin theory

• Oxytocin theory

• Fetal cort

Mechanical factors

• Uterine distension theory

Hormonal factors

• Estrogen theory

• Progesterone withdrawal theory

• Prostaglandin theory

• Oxytocin theory

• Fetal cortisol theory

Stages of labour

Obstetricians have divided labour into 3 stages that delineate milestones in a continuous process

Stages and Phases of labor

• The first stage begins with the onset of labor and ends with full cervical dilation .Friedman subdivided the first stage into latent and active phases

• The Latent phase begins with regular uterine contractions and ends when there is an increase in the rate of cervical dilation

• . It is complete when a nulliparous woman reaches 3– 4 cm dilatation and a parous woman reaches 4– 5 cm . Cervical length should usually be <1 cm . The onset of the latent phase is often difficult to define. According to Friedman the onset of the latent phase is define as the point at which the mother perceives regular contraction

• The active phase is characterized by an increase in rate of cervical dilation and descent of the presenting fetal part .It ends with complete cervical dilation ,and is further subdivided into :

• Acceleration Phase A gradual increase in the rate of dilation initiates the active phase and marks a change in rapid dilation

• Phase of maximum slope, The period of active labor with the greatest rate of cervical dilation

• Deceleration Phase . During the terminal portion of the active phase ,the rate of dilation may slow until full cervical dilation

• .Cervical dilatation rate of 1.2 cm /hr. for nulliparous and 1.5 cm/hr for parous women

First stage of labor

Duration• Primigravida – 8 -12 hours• Multigravida -6-8 hoursLatent phase• In primigravida – 8 hours• In multigravida – 4 hoursActive phase• In primigravida – 4 hours• In multigravida – 2 hours

Stages and Phases of labor

• The second stage of labor is the interval between full cervical dilation and delivery of the neonate

Second stage of labourThe second stage has 2 phases

• Passive: Cervix is fully dilated ,fetal descent continued during the time from full dilatation until an urge to push is felt at about station+ 2 station

• Active :Time from the onset of the urge to push until delivery Presenting part of fetus reaches the pelvic floor. The fetal head will become visible at the introitus ,initially appearing and disappearing between contractions. Once the head is crown ,it does not recede in between contraction .The fetus moves through the birth canal and is completely delivered

Third stage of labour

• The third stage is the interval between delivery of the infant and delivery of the placenta and membranes

• Its duration is 10-20 minutes in both primi and multipara

• The third stage is considered prolonged after 30 minutes, and active intervention ,such as manual extraction of the placenta is commonly considered