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

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)

PARTURITION

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

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

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

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

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

Labor

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

Labor Cervical effacement Cervical dilatation

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

Passage

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

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

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

Labor Progress

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)

Labor Curve

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 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 Nulliparous Multiparous Mean 95th % tile %tile No epidural 53-57 min 122-147 17-19 57-61 Epidural 79 min 185 min 45min 131min

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

CHANGING LABOR STANDARDS

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

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

Does one size fit all?: Fetal Size

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.

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

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

Questions