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Parturition/Stages of Labor
Methodius Tuuli, MD, MPH
Division of Maternal-Fetal Medicine
2
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
5
Mediators of Uterine Activity
6
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
7
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
8
9
Calcium channel
Ca store+ Oxytocin
+ Prostaglandin
Ca+MLCK
Extracellular
Intracellular
Uterine contractions
cAMP
Oxytocin receptor
Phospholipase C
LABOR
10
Labor
Regular uterine contractions
and
Progressive cervical dilatation
11
Labor
• Cervical effacement• Cervical dilatation
12
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
15
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
17
LABOR PROGRESS
18
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
20
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
28
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
34
Does one size fit all?: Fetal Size
46
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.
24
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
44
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
45
Questions