Normal and Abnormal Labor

Normal and abnormal labor

An adequate uterine contraction occurs every 2-3 min; lasts 45-60 sec; and has 50 mm Hg intensity; 100 to 200 M V units.

Stage 1 -latent phase, effacement:

• • Includes latent phase and effacement of cervix. Begins with regular uterine contractions and ends in acceleration of cervical dilation. Typical duration: < 20 hrs in primipara and <14 hrs in multipara.

  • Abnormalities: Prolonged latent phase: Cervix dilated <3 cm. No cervical change in 20 hrs (primipara)/14 hrs (multipara). Most common cause is over analgesia.

  • Management is rest and sedation.

Stage I Active phase dilation:

• Continuation of cervical dilation to completion - 10 cm. Rapid cervical dilation. Duration: > 1.2 cm/hr in primipara, >1.5 cm/hr in multipara.

• Abnormalities: active phase prolongation or arrest: Cervix dilated ≥3 cm or more; cervix dilation is prolonged - <1.2 cm/hr in primipara and <1.5 cm/hr in multipara.

• Arrest occurs when there is no cervical change in ≥2 hours. This is called failure to progress.

• Secondary arrest of labor is defined as no change in cervical dilatation over 2 hr in the active phase. Arrest of descent occurs when there is no descent in the fetal presenting part within 1 hr of complete dilatation

  • Cause: Abnormalities with fetal size or abnormal presentation; pelvis, or dysfunctional contractions.

• Management:

  • Hypotonic contractions: Give Oxytocin IV.

  • Hypertonic contractions: Give Morphine IV sedation.

  • Adequate contractions: Perform emergency cesarean section.

Stage 2 - Descent.

Begins: 10 cm (complete) cervical dilation and ends with delivery of the baby.

Duration: < 2 hrs (primipara); <1 hr (multipara) + 1 hour if epidural.

Abnormalities:

Second stage arrest: Failure to deliver within 2 hours in primipara, and 1 hour in multipara. Add 1 hour if epidural.

Causes: Abnormalities with passenger, pelvis, or power.

Management: If fetal head is not in engaged, do emergency cesarean section. If fetal head is engaged, trials of obstetric forceps or vacuum extraction.

Stage 3- Expulsion.

Begins with the delivery of the baby and ends with the delivery of the placenta.

Duration <30 min.

Abnormalities. Prolonged 3^rd stage with failure to deliver placenta <30 minutes.

Causes: Consider placenta accrete/increta/percreta.

Management:

• • Oxytocin IV

  • If Oxytocin fails, attempt manual removal.

  • Hysterectomy may be needed

Precipitous labor occurs when delivery is within 1 hr of the onset of labor.

A. Uterine contraction monitoring

1) External electronic monitoring will give information on frequency alone, whereas internal electronic monitoring, using a uterine pressure catheter, will give accurate information on both frequency and intensity of contractions in mm Hg.

2) Montevideo units are calculated by multiplying the mean amplitude of the contraction by the number of contractions in 10 min. Women with spontaneous labor, mostly exhibit contraction patterns of >100 Montevideo units.

B. Causes of dysfunctional labor patterns

(a) Loss of synchronization of myogenic, neurogenic, and hormonal mechanisms

(b) Malpresentation

(c) Fetal anomalies

(d) Uterine malformations

(e) Pelvic tumors

(f) Overdistension of uterus

(g) CPD

(h) Extrinsic factors

(i) Sedation

(ii) Anxiety

(iii) Anesthesia

(iv)Supine position

(v) Unripe cervix

(vi)Chorioamnionitis

C. Management

1) Labor augmentation and active management of labor

(a) Sedation with Nubain (10 – 15 mg IM), morphine (10 – 15 mg IM), or Vistaril (100 mg PO) for prolonged latent phase

2) Oxytocin use

(a) Goal of oxytocin augmentation is to produce synchronized regular uterine contractions, which result in cervical dilatation and descent of the fetus, without causing uterine hyperstimulation or fetal compromise.

(b) There is high variability in response to oxytocin.

(c) Oxytocin requires 30 – 40 min to reach steady state .

(d) Oxytocin 6 mU/min infusion with increase in 6 mU/min q15 min to a maximum of 40 mU/min until labor pattern of no more than 7 contractions/15 min is achieved or adequate progress documented.

(e) Hyperstimulation controlled by reducing the dosage of oxytocin, change in maternal position, oxygen to mother, administering tocolytics such as terbutaline or magnesium sulfate.

(f) Other risks of oxytocin use: uterine rupture, water intoxication, cardiac arrhythmias, post-partum H’ge, and allergic reaction.

(g) It is acceptable to use oxytocin trial in VBAC.

3) Amniotomy

(a) Advantages:

(i) Decreased need for oxytocin

(ii) Reduction in labor duration

(iii) Reduction in abnormal 5-min APGAR scores

(b) Risks

(i) Increase in abnormal FHTs leading to increased C-sections for presumed fetal distress.

(c) Use fetal scalp pH monitoring if routine amniotomy is performed to better interpret the abnormal fetal heart rate patterns.

4) Continuous FHR monitoring.

5) Cesarean delivery if no delivery 12 hr post admission or if fetal scalp pH sampling revealed fetal compromise.