Stages of labor

• The first stage (the period of dilatation and effacement) is the interval between the onset of labor (from the begining of regular contracions which occur every 10 minutes, from the moment of rupture of membranes) and full cervical dilatation (10 cm) - the latent phase which comprises cervical

effacement and early cervical dilatation (to 3-4 cm) - the accelerated phase (from 5 to 7 cm) - the transition phase (from 8 to 10 cm)

Stages of laborThe second stage (the period of expulsion) lasts from complete cervical dilatation till the delivery of the infant

The third stage (the placental stage) begins immediately after delivery of the infant and ends with the delivery of the placenta

The fourth stage is defined as the early postpartum period of approximately 2 hours after delivery of the placenta. During this period the patient undergoes significant physiologic adjustment and must be under close medical control

Abnormal labor - dystocia(difficult labor)

It results when:

- anatomic or functional abnormalities of the fetus

- abnormalities of the maternal bony pelvis

- abnormalities of the uterus and cervix

- or combination of these abnormalities

interfere with the normal course of labor

Abnormal labor describes complications of the normal labor process: slower than normal progress or a cessation of

progress

Abnormal labor (or dystocia) is divided into:

- prolongation disorders

- arrest disorders

Patterns of abnormal labor - dystocia:A prolonged latent phase

A latent phase of labor is abnormal when it lasts> 20 hours in primigravid patients> 14 hours in multigravid patients

The causes of such situation:- abnormal fetal position

- „unripe cervix”- administration of excess anesthesia

- fetopelvic disproportion

- disfunctional uterine contractions

A prolnged latent phase does not itself pose a danger to the mother or fetus.

Some patients who are initially thought to have a prolonged latent phase turn out

only to have false labor.

Patterns of abnormal labor - dystocia:A prolonged active phase

An active phase is abnormal when it lasts longer than:

- 12 h in the primigravid patients

- 6 h in the multigravid patients

or when the rate of cervical dilatation is less than

- 1,2 cm/h in primigravid patients

- 1,5 cm/h for multiparas

or when descend of the presenting part is less than

- 1,0 cm/h for primigravidas

- 1,5 cm/h for multiparas

Causes of prolonged active phase:

- abnormal fetal position- fetopelvic disproportion- excessive use of sedation- inadequate contractions- rupture of fetal membranes before the onset of active labor

Patterns of abnormal labor- dystocia:Arrest disorders:

Secondary arrest of dilatation:

no cervical dilatation for > 2 h in any case in the active phase of labor

Arrest of descend:

no descent of the presenting part in > 1 h in the second stage of labor

It occurs when:

- the contractions are no longer sufficient to maintain the progress of labor

orthe labor arrests in spite of adequate uterine

contractions associated with:- too large fetus

- fetal lie or position that prevents progress in labor- too small or abnormally shaped pelvis

Correct diagnosis and management of abnormal labor requires evaluation of the mechanisms of labor:

- the power (uterine contractions)- the passenger (fetal factors - presentation, size)- the passage (maternal pelvis)

Evaluation of the power includes:strenght, duration and frequency of uterine

contractions

- manual palpation of the maternal abdomen during

a contraction (subjective evaluation)

- external tocography (more objective) - a tocodynamometer is an

external strain gauge, which is placed on the maternal abdomen, it records

when the uterus tightnes and relaxes but does not directly measure how

much force the uterus is generating for a given contraction

- internal tocography (the most objective) - an intrauterine pressure

catether is placed into the uterine cavity and it transmits the actual

intrauterine pressure to the external strain gauge, which then records

duration and frequency as well as the strength of the contractions

For cervical dilatation to occur, each contraction must generate at least 25 mm Hg of pressure. The optimal intrauterine pressure during contraction is

50-60 mm Hg.

In generating a normal labor pattern the frequency of contractions is also very important. A minimum

three contractions in a 10 minute window is usually considered adequate.

During the first stage of labor arrest of labor should not be diagnosed until the cervix is at least 4 cm dilated (before ending the latent phase of labor).

During the second stage of labor, the „power” include both, the uterine contractile forces and the voluntary

maternal expulsive efforts (pussing)

Evaluation of the passenger

This includes:

- estimation of the expected fetal weight-clinical evaluation of fetal lie, presentation, position

If the estimated fetal weight is > 4000 g the incidence of dystocia, including shoulder dystocia or fetopelvic

disproportion is greater.

Cephalopelvic disproportion is a disparity between the size or shape of the maternal pelvis and the fetal head

If the fetal head is extended a larger cephalic diameter (> 32 cm) is presented to the pelvis, therby

increasing the possibility of dystocia

A brow presentation (forehead - the largest cephalic diameter

is 36 cm) (1/3000 deliveries) typically converts to either a vertex or face presentation, but if persistent,

causes dystocia requiring cesarean section.

A face presentation also requires cesarean section in most cases, although a mentum anterior presentation (chin toward

mother’s abdomen) sometimes may be delivered vaginally.

Persistent occiput posterior positions are also associated with longer labors (about 1 hour in

multiparous patients and 2 hours in nulliparous patients)

Fetal anomalies like hydrocephaly and soft tissue tumors may also cause dystocia. The use of prenatal

ultrasound significantly reduces the incidence of unexpected dystocia for these reasons.

Evaluation of the passageMeasurements of the bony pelvis are relatively poor predictors of successful vaginal delivery. It depends on the inaccuracy of these measurements as well as case-by-case differences in fetal accomodation and mechanisms of labor. Only in rare cases, when the

pelvis is „completely contracted” (the pelvic diameters are very small) manual evaluation of the

diameters of the pelvis can predict that the fetus will not passage the birth canal.

In some cases the X-ray or computed tomographic pelvimetry can be helpful, but the best test of pelvic adeqacy is the progress or lack of progress of descending of the fetal presenting part in the birth canal.

Except the bony pelvis, there are soft tissues causes of dystocia, such as: -distended bladder or colon, -adnexal mass-uterine fibroid

Management of abnormal labor

Augmentation of labor is the stimulation of uterine contractions that began spontaneously but

are either too infrequent or too weak, or both.

Induction of labor is the stimulation of uterine contractions before the spontaneous onset of labor,

with the goal of achieving delivery.

Stimulation or induction of labor is usually carried out with intravenous oxytocin (sometimes

prostaglandines) administrated by means of metered pump.

The incidence of prolongation of the first stage of labor can be minimized by avoiding unnecessary

intervention, i.e:

labor should not be induced when the cervix is not well prepared or ripe (softened, anteriorly rotated,

partially effaced)

The Bishop score is used to quantify the degree of cervical ripening and readiness for labor.

Factor 0 1 2 3

Dilation Closed 1-2 cm 3-4 cm > 5 cm

Effacement 0-30% 40-50% 60-70% > 80%

Station > - 3 -2, -1 0 +1, +2

Consistency Firm Medium Soft

Position Posterior Mid Anterior

A score of 0 to 4 points is associated with the highest likelihood of failed induction.

A score of 9 to 13 points is associated with the highest likelihood of successful induction

Induction of labor is indicated if the anticipated

benefits of delivery exceed the risks of allowing the pregnancy to continue

Indications

• Post-term pregnancy• Maternal medical problems• Pregnancy-induced hypertension• Premature rupture of membranes• Chorioamnionitis

Contraindications

• Placenta or vasa previa• Cord presentation• Abnormal/unstable fetal lie• Prior two or more cesarean sections• Prior classical uterine incision• Prior uterine incision of unknown type• Active genital herpes

When the cervix is unripe, Prostaglandin E2 (Prepidil, Propess) is administrated intracervically

or to the posterior fornix of the vagina. In the majority of these cases labor begins without the

need of oxytocin stimulation.

A prolonged latent phase can be managed by either rest or augmentation of labor with

intravenous oxytocin after excluding mechanical factors.

If the patient is allowed to rest, one of following will occur:

- the conractions can stop, in which case the patient is not in labor (false labor)

- the contractions can become more frequent and intensive, in which case the patient will go into

active labor- the contractions may be as before, in which case oxytocine may be administrated to augment the

uterine contractions

The use of amniotomy (artificial rupture of membranes) is also advocated with prolonged latent phase.

After amniotomy the fetal head will provide a better dilating force than would the intact bag of waters. Additionaly there

may be a release of prostaglandines, which could aid in augmenting the force of contractions.

The risk of amniotomy is:- an umbilical cord prolapse (the presenting part should be firmly applied to

the cervix)

- abruption of the placenta- intrauterine infection

In the active phase of labor mechanical factors such as abnormal position or

presentation as well as fetopelvic disproportion must be considered before use

of oxytocin.

If the woman is tired which results in secondary arrest of dilation, rest followed by

augmentation with oxytocin is often effective. Artificial rupture of the membranes is also

recommended.

Risks of prolonged laborMaternal Fetal

• infection• maternal exhaustion• lacerations• uterine rupture• uterine atony with

possible hemorrhage

• asphyxia• trauma • infection• cerebral damage

Prolonged labor is associated with the passage of meconium into the amniotic fluid and subsequently the risk of meconium aspiration syndrome (MAS).

Fetuses who inhale meconium-stained fluid during labor may suffer this syndrom, which includes both mechanical obstruction and chemical pneumonitis from the meconium material.Pathologic factors include:- atelectasis- consolidation- barotrauma- removal of pulmonary surfactant by free fatty acids

Amniodilution is a method of intrapartum treatment of meconium-stained amniotic fluid. A normal saline solution is slowly infused through a tube inserted in the uterus, washing meconium-stained fluid out and

replacing it with the saline solution.

As the fetal head is delivered, but before delivery of the fetal chest, suctioning of the nasopharynx should be performed. After delivery of the fetus suctioning out of meconium in the deeper parts of respiratory

tract (below the vocal cords) must be done.

Techniques of operative delivery include:- obstetric forceps

- vacuum extraction- cesarean section

The purpose of the forceps maneuver is to:

1. augment the forces expelling the fetus when the mother’s voluntary efforts in

conjunction with uterine contractions are insufficient to deliver the infant

and eventually to:

2. rotate the fetal head in the birth canal, if it isn’t completely rotated

Necessary conditions to apply forceps:

• Cervix Fully dilated• Membranes Ruptured• Position and station

of fetal head Known and engaged

• Feto-pelvic disproportion Excluded

• Fetus Alive

Forceps Classification

• Outlet forceps - the fetal skull has reached the perineal floor, the scalp is visable between contractions, the sagittal suture is in the anteposterior diameter

• Low forceps - the leading point of fetal skull is +2 station or more

• Midforceps - the head is engaged but the leading point of the skull is above +2 station

• High forceps - the head is high above inlet and isn’t engaged, the leading point of the skull above 0 (not performed in current obstetrics)

To avoid the potential risk of trauma to both maternal and fetal parts application of obstetric forceps should be performed

by an experienced clinician

Before application of the forceps the physician should reassess the fetal position.

The neonatologist should be notified in advance, before application of the forceps.

Forceps should be applied only after the cervix is completely dilated and if there is no evidence of

cephalopelvic disproportion.

Forceps sshould be applied only (!!) after the biparietal diameter has passed through the inlet, and

the skull has passed below the ischial spines.

After delivery the genital tract and infant should be examined carefully.

Potential risks:- lacerations of: the cervix, vagina, perineum,

bladder and rectum- injuries of the fetus: intracranial hemorrhage, skull

fracture, brachial plexus injury, cephalhematoma, facial paralysis, clavicular fracture

Vaccum extractionThis maneuver is similar to forceps delivery.

Its purpose is to augment the forces expelling the fetus when the mother’s voluntary efforts in

conjunction with uterine contractions are insufficient to deliver the infant.

Advantages of the vacuum extractor include:

- less force applied to the fetal head

- reduced anesthesia requirements

- easier aplication

- less perineal trauma-the ability to permit the head to find its path out

of the maternal pelvis

Disadvantages of the vacuum extractor include:

- the application of traction only during contractions- limitation of its use only to term infant- prolonged delivery in comparison to forceps delivery

The head must be engaged and the membranes must be ruptured. There is no danger of catching vaginal mucosa or cervical tissue between the vacuum and the fetal head. Traction should be applied during the contraction with the mother bearing down. A safety feature of the vacuum cup is its inability to remain on the fetal head during excess traction which may occur during forceps delivery.

Cesarean section

About 20-25% of gravidas are now delivered by cesarean section. Appropximately two-thirds of

these procedures are perforemd after the onset of labor.

In elective or not very emergency situations such as - abnormal presentation- placenta previa without bleeding- large fetus- abnormal pelvis- some maternal diseases- prolonged labor- begining of fetal depresiontransverse abdominal incision in the lower part of abdomen, just above the pubic bone, is performed (bikini cut). In such situations there is sufficient time to use regional anesthesia which allows the mother to be awake without feeling pain (spinal block or an epidural catheter).

In emergency situations such as:- fetal depresion- prolapsed umbilical cord- ruptured uterus- severe abruptio placente- placenta previa with extensive hemorrhagea midline vertical abdominal incision (from the nevel to the pubic bone) provides more rapid access to the uterus. In such situations general anesthesia and endotracheal intubation is the preferred technique.