Parturition/Stages of Labor

Methodius Tuuli, MD, MPH

Division of Maternal-Fetal Medicine

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Objectives

1. Describe physiology of labor

2. Define stages of labor

3. Discuss concepts of normal labor progress– Traditional (Friedman’s)– Contemporary (Zhang’s)– Custom labor curve (Cahill/Tuuli)

PARTURITION4

Parturition

• Early Pregnancy– Uterine quiescence– Closed cervix

• Parturition– Coordinated uterine activity– Cervical remodelling – Progressive cervical dilation

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Mediators of Uterine Activity

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Inhibitors•Progesterone•Prostacycline•Relaxin•Nitric Oxide•Parathyroid hormone-related peptide

•CRH•HPL

Quiescence

UterotoninsProstaglandinsOxytocin

Stimulation

UterotrophinsEstrogen•Progesterone•Prostaglandins•CRH

Activation

InvolutionOxytocin•Thrombin

Involution

Initiation of Labor• Fetus

– Sheep

• Fetal ACTH and cortisol

– Placental 17 α hydroxylase Estradiol Progesterone

– Placental production of oxytocin, PGF2 α

– Humans

• Fetal increased DHEA

– Placental conversion to estradiol

– Increased decidual PGF2 and gap junctions

– Increased oxytocin and PG receptors

– Changes in progesterone receptors

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Initiation of Labor

• Oxytocin– Peptide hormone– Hypothalamus-posterior pituitary– Oxytocin receptors

• Fundal location• 100-200 x during pregnancy

– Actions• Stimulate uterine contractions• Stimulate PG production from amnion/decidua

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Calcium channel

Ca store+ Oxytocin

+ Prostaglandin

Ca+MLCK

Extracellular

Intracellular

Uterine contractions

cAMP

Oxytocin receptor

Phospholipase C

LABOR

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Labor

Regular uterine contractions

and

Progressive cervical dilatation

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Labor

• Cervical effacement• Cervical dilatation

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Labor: the three “P’s”

• Passage

• Passenger

• Powers

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Passage

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Passenger

• Size– Estimated fetal weight

• Lie– Longitudinal– Transverse/oblique

• Presentation– Vertex 95%

– Non-vertex 5%

• Station• Position

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Passenger: cardinal movements of labor

• Descent• Flexion• Internal rotation• Extension• External rotation• Expulsion

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Powers

• Uterine contractions– Duration 30-60 seconds

– 3-5 contractions / 10 minutes

– Montevedeo units (intrauterine catheter)

• Baseline to peak

• Sum over 10 minutes

• Adequate: >200-250 MVU

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LABOR PROGRESS

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Stages of Labor

• First stage – onset of labor to complete dilatation

– Latent phase– Active phase

• Second stage – complete cervical dilation to expulsion of fetus

• Third stage – expulsion of fetus to expulsion of placenta

• (Fourth Stage – First hour after expulsion of placenta)

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Labor Curve

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First Stage

• Latent phase – onset to rapid cervical change• Active phase – rapid cervical change to complete

dilatation• Traditional standards

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Nulliparous Multiparous

Mean95th

% tileMean

95th

%tile

Latent phase

7.3-8.6hr 17-20 hr 4.1-5.3hr 12-14 hr

Active phase

1.5cm/hr 1.2cm/hr

Second Stage

• Traditional standards

• Immediate versus delayed pushing• Spontaneous versus coached pushing

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Nulliparous Multiparous

Mean95th

% tileMean

95th

%tile

No epidural53-57min

122-147min

17-19min

57-61min

Epidural 79 min 185 min 45min 131min

Third Stage

• Standards– Mean – 6 minute– 97th% tile – 30 minutes

• Active versus passive

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CHANGING LABOR STANDARDS

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Why concern?

Too many cesarean

Why concern?

1955: Friedman’s Labor Curve

• Convenience sample – 622 consecutive nullips– 500 with adequate data

• Cervical dilation (Y) plotted against time (X)

• Major advance in his day

“…..introduces a new dimension to us. Evaluation of progress, previously synonymous with nebulous degree of change, becomes available to us in terms of specific change.”

Traditional labor curve: Friedman’s

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Limitations of Friedman’s Curve

• Non-representative sample• More ‘graphical’ than ‘statistical’

– Did not take into account special characteristics of labor data

• Adopted without complete context– Subject characteristics– Interventions

2002: Zhang’s Labor Curve

• Took into account the unique features of labor data– Left censored– Interval censored– Repeated measures– Log-normal distribution

• ‘Appropriate’ analytical tools– Repeat ed measures regression curves– Interval censored regression models medians (95th tile)

• Contemporary sample

2002: Zhang’s Labor Curve

2002: Zhang’s Labor Standard

Zhang’s curve: key concepts

• Transition to active labor after 6cm dilation; not 4cm. • No deceleration phase • Traverse times

– much longer in latent phase– much shorter in active phase

TOWARDS CUSTOM LABOR STANDARDS

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Does one size fit all?: Fetal Size

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810

Cer

vica

l Dila

tion

(cm

)

0 2 4 6 8Duration of labor (hours)

<2500g 2500-3000g3000-3500g 3500-4000g>4000g

Does one size fit all?: Fetal Sex

Cahill AG, Roehl KA, Odibo AO, Zhao Q, Macones GA. Am J Obstet Gynecol. 2012 Apr;206(4):335.e1-5.

Does one size fit all? Maternal Race

Does one size fit all? Induced labor

Harper LM, Caughey AB, Odibo AO, Roehl KA, Zhao Q, Cahill AG. Obstet Gynecol. 2012 Jun;119(6):1113-8.

Does one size fit all? Induction method

Tuuli MG, Keegan MB, Odibo AO, Roehl K, Macones GA, Cahill AG. Am J Obstet Gynecol. 2013 Sep;209(3):237.e1-7.

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68

10C

ervi

cal D

ilatio

n (c

m)

0 5 10 15 20Duration of Labor (hours)

Misoprostol Foley Catheter

Average Labor Curves: Misoprostol versus Foley Catheter

Does one size fit all?: Maternal Obesity

Norman SM, Tuuli MG, Odibo AO, Caughey AB, Roehl KA, Cahill AG. Obstet Gynecol. 2012 Jul;120(1):130-5.

Custom Labor Curve: the Holy Grail

Seeks to incorporate the multiplicity of individual patient factors in estimating expected labor progress

• Has been methodologically challenging• Recent progress

– N=5000– Detailed labor data– Collaboration with statisticians– Mathematical model incorporating

• Parity• Epidural• BMI• Labor type

Custom Labor Curve: the Holy Grail

Custom Labor Curve: the Holy Grail

• Next steps– Validate in independent data set (N=4000)– Refine model to include time variable factors– Software development– RCT to assess impact on cesarean rate

Summary

• Labor involves transition of the uterus from a quiescent state to regular contractions and cervical dilation resulting in delivery of the fetus and placenta

• Initiation of labor in humans is incompletely understood, but involves maternal-fetal-placental interactions

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Summary

• Clinical management of labor requires understanding of the normal progress

• Our understanding of normal progress of labor is evolving towards more ‘customized’ individualized standards

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Questions