••• Chapter 5^ Labor and Delivery^57
❍ What is the <5th percentile for nulliparous patients?
<.2 cm/h.
❍ What is the <5th percentile for multiparous patients?
<1.5 cm/h.
❍ What is the definition of the secondary arrest of labor?
It is defined as lack of cervical change for 2 hours following normal dilatation.
❍ What are the most common units used to describe uterine activity?
Montevideo units, a uterine activity unit.
❍ How are these units defined?
Montevideo units refer to the strength of contractions in mm of mercury multiplied by the frequency per
10 minutes. The uterine activity unit is defined as 1 mmHg/min.
❍ When is oxytocin indicated?
When uterine activity is <50 mgHg every 3 minutes or <200 Montevideo units.
❍ What is the duration (half-life) of intravenous oxytocin?
The half-life is 3 to 4 minutes.
❍ Name a maternal systemic effect of oxytocin.
Antidiuresis.
❍ An anthropoid pelvis is often associated with what presentation?
Occipitoposterior.
❍ An android pelvis is often associated with?
Deep transverse arrests.
❍ A transverse presentation is frequently seen with which pelvis type.
Platypelloid.
❍ What percentage of women have a gynecoid pelvis?
Approximately 50% making this the most common pelvis type.
❍ The critical distance of the anterior-posterior diameter of the pelvis is?
10 cm.
❍ The uterus receives what percentage of cardiac output at term?
Approximately 10%.