1. Parturition/Stages of Labor
Methodius Tuuli, MD, MPH
Division of Maternal-Fetal Medicine

3. Objectives Describe physiology of labor Define stages of labor
Discuss concepts of normal labor progress
Traditional (Friedman’s)
Contemporary (Zhang’s)
Custom labor curve (Cahill/Tuuli)

4. PARTURITION

5. Parturition Early Pregnancy Parturition Uterine quiescence
Fetus
Mother
Membranes
Placenta
Early Pregnancy
Uterine quiescence
Closed cervix
Parturition
Coordinated uterine activity
Cervical remodelling
Progressive cervical dilation

6. Mediators of Uterine Activity
Inhibitors
Progesterone
Prostacycline
Relaxin
Nitric Oxide
Parathyroid hormone-related peptide
CRH
HPL
Quiescence
Uterotrophins
Estrogen
Progesterone
Prostaglandins
CRH
Activation
Uterotonins
Prostaglandins
Oxytocin
Stimulation
Involution
Oxytocin
Thrombin

7. 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

8. Initiation of Labor Oxytocin Peptide hormone
Hypothalamus-posterior pituitary
Oxytocin receptors
Fundal location
x during pregnancy
Actions
Stimulate uterine contractions
Stimulate PG production from amnion/decidua

9. Uterine contractions cAMP + Oxytocin + Prostaglandin Oxytocin receptor
Extracellular
Calcium channel
Intracellular
Phospholipase C
cAMP
Ca+
MLCK
Ca store
+ Oxytocin
+ Prostaglandin
Oxytocin binds receptor and activates phospholipase c. PHC increase intracellular Ca by release of intracellular calcium and promote influx of calcium. Ca binds myosin light chain kinase
Uterine contractions

10. Labor

11. Regular uterine contractions and Progressive cervical dilatation
Labor
Regular uterine contractions and Progressive cervical dilatation

12. Labor
Cervical effacement
Cervical dilatation

13. Labor: the three “P’s”
Passage
Passenger
Powers

14. Passage

15. Passenger Size Lie Presentation Station Position
Estimated fetal weight
Lie
Longitudinal
Transverse/oblique
Presentation
Vertex 95%
Non-vertex 5%
Station
Position

16. Passenger: cardinal movements of labor
Descent
Flexion
Internal rotation
Extension
External rotation
Expulsion

17. Powers Uterine contractions Duration 30-60 seconds
3-5 contractions / 10 minutes
Montevedeo units (intrauterine catheter)
Baseline to peak
Sum over 10 minutes
Adequate: > MVU

18. Labor Progress

19. 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)

20. Labor Curve

21. First Stage Latent phase – onset to rapid cervical change
Active phase – rapid cervical change to complete dilatation
Traditional standards
Nulliparous
Multiparous
Mean
95th
% tile
%tile
Latent phase hr
17-20 hr hr
12-14 hr
Active phase
1.5cm/hr
1.2cm/hr

22. Second Stage Traditional standards Immediate versus delayed pushing
Spontaneous versus coached pushing
Nulliparous
Multiparous
Mean
95th
% tile
%tile
No epidural
53-57
min
17-19
57-61
Epidural
79 min
185 min
45min
131min

23. Third Stage Standards Active versus passive Mean – 6 minute
97th% tile – 30 minutes
Active versus passive

24. CHANGING LABOR STANDARDS

25. Why concern?
Too many cesarean

26. Why concern?

27. 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.”

28. Traditional labor curve: Friedman’s

29. 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

30. 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

31. 2002: Zhang’s Labor Curve

32. 2002: Zhang’s Labor Standard

33. 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

34. TOWARDS CUSTOM LABOR STANDARDS

35. Does one size fit all?: Fetal Size

36. Does one size fit all?: Fetal Sex
Cahill AG, Roehl KA, Odibo AO, Zhao Q, Macones GA. Am J Obstet Gynecol Apr;206(4):335.e1-5.

37. Does one size fit all? Maternal Race

38. Does one size fit all? Induced labor
Harper LM, Caughey AB, Odibo AO, Roehl KA, Zhao Q, Cahill AG. Obstet Gynecol Jun;119(6):

39. Does one size fit all? Induction method
Tuuli MG, Keegan MB, Odibo AO, Roehl K, Macones GA, Cahill AG. Am J Obstet Gynecol Sep;209(3):237.e1-7.

40. Does one size fit all?: Maternal Obesity
Norman SM, Tuuli MG, Odibo AO, Caughey AB, Roehl KA, Cahill AG. Obstet Gynecol Jul;120(1):130-5.

41. 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

42. Custom Labor Curve: the Holy Grail

43. 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

44. 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

45. 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

46. Questions