Labor and Delivery Care Module 3 + 4

Sympathetic input for FHR

releases catecholamines that increase the heart rate. Primary control of the FH until the second trimester.

Parasympathetic input for FHR

A. mediated by the Vagus nerve. Becomes dominate over the sympathetic in the second trimester. Gradually slows the HR down.

Chemoreceptors

sensitive to changes in oxygen and CO2 in the blood. Increased CO2 makes chemoreceptors send signals to the medulla oblongata, which stimulates the vagus nerve and slows down FH.

Baroreceptors

in the aortic and carotid arches. Rapidly detect changes in blood pressure. When blood pressure goes up, a quick reflex is sent to the vegal nerve to slow the FHR.

fetal bradycardia

cause may be hypoxic and nonhypoxic. Not associated with acidemia when it has moderate variability. FH >80 will preserve coronary and cerebral oxygenation. <80 will cause variability to diminish and metabolic acidemia. <60 is an emergency.

hypoxic fetal bradycardia

cord prolapse, placental abruption, uterine rupture, and vasa previa. May be result of progressive hypoxia that overwhelms the fetal compensatory mechanisms.

Nonhypoxic fetal bradycardia

heart block and maternal hypothermia. May be idiopathic with postdates babies. Can develop with rapid decent of fetus (head compression leading to increased ICP -> vagal response and bradycardia). Also caused by maternal hypotension with anesthesia.

Fetal Tachycardia

mild is normal in <28 weeks. May be caused by medications given to correct maternal hypotension. May be caused by developing hypoxia (with decels), infections, arrhythmias, fetal anemia, or maternal hyperthyroidism.

Early deceleration

exact mechanism is not determined. Common theory is head compression. Not associated with acidemia. If recurrent, may turn into lates.

Late decelerations

occur in response to transient decreases in oxygen tension. Starts with uterine ctx that causes decrease in uteroplacental perfusion which is followed by lower oxygen levels in the blood returning from the placenta to fetal circulation. Chemoreceptors are activated and drop the FH.

Why lates happen after the peak of a ctx

the CNS needs time to first detect the physiologic pathway that results in chemoreceptor stimulation then generate a response via the vagus nerve.

Late decelerations with moderate variability

indicate a fetus with normal CNS status having an expected, compensatory response to decreased oxygenation related to ctx. No indicative of acidemia

Late decelerations without variability

closely associated with fetal acidemia. Decelerations get deeper as acidemia worsens. May be due to direct myocardial depression that occurs when fetal compensatory mechanisms are insufficient to maintain adequate cerebral and myocardial oxygenation.

Variable deceleration

most common decel. Thought to be caused by umbilical cord occlusion that causes an increase in fetal peripheral resistance and hypertension. This triggers baroreflex-mediated decelerations to restore normal arterial pressure. Chemoreceptors also respond to abrupt reductions in fetal oxygenation related to interruptions in umbilical blood flow r/t cord compression.

Minimal variability

without decels, no correlation of fetal acidemia, may be a rest cycle. May also be caused by admin of opioids, Phenergan, or terb.

Absent variability

without decels may be idiopathic and not associated with acidemia. Cat 3 if happening with decels and reflects fetal acidemia.

Sinusoidal pattern

extremely rare. Develops when fetus is experiencing clinically significant anemia. Usually d/t Rh isoimmunization or maternal-fetal hemorrhage following vasa previa, uterine rupture, or placental abruption.

Category I (normal) characteristics

o baseline rate 110-160.

o Moderate variability

o Absence of lates or variables (earlies are ok)

o Accels are present or absent

Category II (indeterminate) characteristics

o anything that is not cat I or III.

o Bradycardia or tachycardia (without absent variability)

o Minimal, absent, or marked variability

o no accels after scalp stim

o decels with min or mod variability

o prolonged decels <10mins

o lates with moderate variability

Category III (abnormal) characteristics

o Absent baseline with

§ Recurrent lates

§ Recurrent variables

§ Bradycardia

o Sinusoidal pattern

Recommendations for the frequency of FH assessment during first stage of labor

o ACOG - q30 minutes

o ACNM + AWHONN - q15-30 minutes

· Recommendations for the frequency of FH assessment during second stage of labor

o ACOG - q15min

o ACNM- q15 then q5 with pushing

o AWHONN - q5-15

heart rate characteristics that can be assessed with intermittent auscultation.

· Baseline FH

· Occurrence of brief increases and decreases in the FH

· Audible arrhythmias

Intermittent auscultation Category I (normal)

FHR baseline between 110-160bpm with regular rhythm

No decreases of the FHR from the baseline

FH increases of 15 secs in duration. Amplitude from baseline may or may not be present

Intermittent auscultation Category II (indeterminate)

Tachycardia >160 or bradycardia <110

Audible irregular rhythm

Presence of FHR decreases

· Management of cat II FH with IA

o Increased surveillance - longer listening period, increased frequency, or transfer to EFM

o Change positions, IVF, oxygen, tocolytics

The relationship between intrapartum asphyxia and neurological injury in the fetus.

· Most cerebral palsy is not caused by intrapartum asphyxia

· There are established criteria necessary of defining an "acute intrapartum hypoxic event as sufficient to cause cerebral palsy"

· Abnormal FH alone does not indicate intrapartum asphyxia

Friedman's first stage of labor

o Divided into latent and active phase

o Latent phase begins with the onset of regular contractions

o Active phase begins when the rate of progress increases (3cm)

o Ends with complete dilation

Friedman's second stage of labor

o Begins with complete dilation

o Ends with birth of baby

· Friedman’s definition of active labor vs current research

o Friedman said active labor is when rate of progress increases, usually 3cm

o Current research says active labor is 5-6cm

o Misdiagnosing active labor results in unnecessary intervention

Friedman criteria for latent phase of labor length

o Calculated based on total duration, not rate of change per hour

o Nulliparas: <20hr

o Multiparas: <14 hr

Friedman criteria for active phase of labor length

o Calculated based on cm

o Nulliparas: at least 1.2cm/hr

o Multiparas: at least 1.5cm/hr

· Friedman criteria for second stage of labor length

o Nulliparas: 1cm/hr decent

o Multiparas: 2cm/hr

Friedman’s Protracted descent

o only diagnosed in second stage

o progress is occurring but slower than normal

Friedman’s arrest of dilation

o No dilation in 2 hours

Friedman’s Secondary arrest of dilation

o States the 2 hour time frame is arbitrary

o More than half of women with arrested labor gave birth vaginally with no intervention

o Calls into question abnormality of no progress for 2 hours

Friedman’s Arrest of descent

o Only diagnosed in second stage

o No progress made

o No decent in 1 hour

Friedman’s method for determining time limits of labor

o Take upper limit of normal for each stage and phase in total hours, then divide by number of cm

o This calculates upper limit of normal in terms of hourly progress of dilation and decent

Contemporary research on labor duration

o Rate of dilation increases as labor progresses

o Normal progress is:

§ 0.5-0.7cm/hr in nullips

§ 0.5-1.3cm/hr in multips

Arrested labor based on contemporary research

o No progression in cervical dilation in patients who are at least 6cm dilated with ROM

o Despite 4hr of adequate ctx OR 6hr of inadequate ctx with oxytocin augmentation

Evidence and expert opinion regarding when we should intervene in slow labor

o After 4 hours with no progress, consider amniotomy or pit

o Should only intervene in active labor, not latent

When a cesarean birth indicated/appropriate for slow labor

o Slow labor is not an indication alone for c/s

o If cervical dilation is at least 6cm with ROM and there has been no change in 4 hours

o There is adequate uterine activity or at least 6 hours of pit when unable to attain adequate uterine activity

Contraindications of induction of labor

o Any situation that precludes vaginal birth:

o Placenta/vasa previa

o Transverse lie

o Umbilical cord prolapse

o Previous myomectomy entering the endometrial cavity

o Previous classical uterine incision

o Active genital herpes infection

o Presence of a cat III tracing

possible complications of oxytocin use in labor

o Desensitization and increase risk of PPH

o Antidiuretic effect

o Can cause hypotension, tachycardia, and transient myocardial ischemia

o Uterine tachysystole

o Increased risk of uterine rupture

o EFM changes

Oxytocin dosing

o Variability in individual response - start at a small dose and titrate

o Dependent on the development of receptors in myometrial tissue just before and during labor to exert its effects

o Newer evidence shows d/c pit in active labor to reduce risk of uterine tachysystole and abnormal FHR

High dose oxytocin

o Start at 6mU/min increase by 3-6 q15-40

o Associated with uterine tachysystole, and a shorter interval between starting pit and active labor

o Shorter duration of labor

o Not associated with increased c/s rate

Prostaglandins and IOL

o Prostaglandin receptors are always present in myometrial tissue, so prostaglandins can be used to induce at any gestational age

o Soften the cervix and stimulate myometrial ctx

o Contraindicated in people who have had a prior C/S or uterine surgery

Common prostaglandins used in OB

o Misoprostol (Cytotec)- PGE1 for IOL and TOP

o Dinoprostone (Cervidil or Prepidil) - PGE2 for IOL and TOP

o Carboprost (Hemabate) - PGF2 for PPH and TOP

Misoprostol (Cytotec) PGE1

o Not approved by the FDA for cervical ripening (off lable use)

o Contraindicated in TOLAC

o Vaginal doses are associated with higher incidences of tachysystole

Dinoprostone (Cervidil) PGE2

o Approved by the FDA for cervical ripening

o Available in gel (prepidil) and vaginal insert (cervidil)

Cervical balloons

o Most common method of mechanical dilation

o Works directly on the cervix by applying pressure that helps it dilate and increases the tissues response to oxytocin and prostaglandins

o larger fill volumes are associated with shorter labor durations

o risk for accidental ROM or cervical bleeding

The Bishop Score

o Used to predict the success of induction and need for cervical ripening

o Numeric assessment of four different characteristics of the cervix and fetal station

o Indicates whether the cervix is "favorable" or "unfavorable"

Bishop score of a “ripe” cervix

o Score of 8 or greater in a nullip

o Score of 6 or greater in a multip

o Anything less than these is considered unfavorable and ripening is recommended

“other” methods of cervical ripening and IOL

o Sex

o Membrane sweeps

o Nipple stim

o Pineapple

o Castor oil

o Red raspberry leaf tea

o Evening primrose oil

o Date fruit

o Acupuncture

o Blue and black cohosh

Active management of labor

o Package of care the originated in Dublin Ireland in the 1970s

o OB/GYNs guaranteed birth within 12 hours of hospital admission

o No admission until active labor

o Continuous support by a midwife

o Strict progress protocols and interventions in the absence of "adequate" progress

o Decreased c/s rate from 10% to 5%