Normal labor physiology Flashcards
(5 cards)
What is the primary role of prostaglandins during labor?
Choose the correct answer
A) To relax the uterine muscles
B) To increase cervical softening and dilation
C) To inhibit oxytocin release
D) To suppress myometrial activity
B) To increase cervical softening and dilation
B) To increase cervical softening and dilation
Prostaglandins — especially PGE2 and PGF2α — play critical roles in the initiation and progression of labor:
Cervical Ripening (Softening, Effacement, Dilation):
PGE2 promotes collagen degradation and increased water content in the cervix.
This facilitates cervical softening and dilation, preparing for fetal descent.
Uterine Contractility:
PGF2α increases myometrial contractions, synergizing with oxytocin.
📖 Williams Obstetrics, 25th ed.:
“Prostaglandins play a pivotal role in cervical ripening and myometrial activation, both essential for labor progression.”
📖 ACOG – Induction of Labor (Practice Bulletin):
“Prostaglandins such as PGE2 are used clinically for cervical ripening, and endogenous PGs rise before labor onset, contributing to cervical changes and increased uterine activity.”
❌ Why the others are incorrect:
To relax the uterine muscles → Opposite; prostaglandins stimulate contractions.
To inhibit oxytocin release → Incorrect; prostaglandins actually enhance oxytocin’s effect.
To suppress myometrial activity → Incorrect; prostaglandins stimulate uterine muscle.
Which hormone is primarily responsible for stimulating uterine contractions during labor?
Choose the correct answer
Progesterone
Oxytocin
Prostaglandin E2
Estrogen
Oxytocin
Oxytocin is the primary hormone responsible for stimulating uterine contractions during active labor.
It is released by the posterior pituitary gland and acts on oxytocin receptors in the myometrium, which:
Increase in number and sensitivity toward term (upregulated by estrogen)
Trigger strong, rhythmic uterine contractions
📖 Williams Obstetrics, 25th ed.:
“Oxytocin is a potent stimulant of uterine smooth muscle, and plays a key role in the augmentation and maintenance of labor.”
📖 ACOG Practice Bulletin – Induction of Labor:
“Oxytocin is the most commonly used agent to initiate or augment uterine contractions during labor.”
❌ Why the other options are incorrect:
Progesterone → Maintains uterine quiescence during pregnancy; its withdrawal facilitates labor onset.
Prostaglandin E2 (PGE2) → Important for cervical ripening and also supports contractions but is not the primary stimulator.
Estrogen → Upregulates oxytocin receptors and PG synthesis, but doesn’t directly cause contractions.
Which of the following best describes the cardinal movement of “engagement” during labor?
Choose the correct answer
The fetus rotates so that the occiput is anterior in the maternal pelvis.
The biparietal diameter of the fetal head passes through the pelvic inlet.
The fetus descends into the vaginal canal.
The fetal shoulders are delivered after the head.
The biparietal diameter of the fetal head passes through the pelvic inlet.
Engagement – Defined:
Engagement refers to the point during labor when the widest part of the fetal head — specifically the biparietal diameter (BPD) — enters and passes through the pelvic inlet.
It confirms that the presenting part is in the pelvis and labor is progressing.
📖 Williams Obstetrics, 25th ed.:
“Engagement is said to occur when the biparietal diameter of the fetal head has passed through the plane of the pelvic inlet.”
❌ Why the other options are incorrect:
“The fetus rotates so that the occiput is anterior…” → This describes internal rotation, not engagement.
“The fetus descends into the vaginal canal.” → This describes descent, a separate movement.
“The fetal shoulders are delivered after the head.” → This describes the movement of expulsion.
Which of the following is the most accurate definition of the latent phase of labor?
Choose the correct answer
The period of strong, regular uterine contractions with progressive cervical dilation
The period between complete cervical dilation and delivery of the baby
The period of slow cervical dilation and effacement with irregular contractions
The period of active pushing during the second stage of labor
The period of slow cervical dilation and effacement with irregular contractions
Latent Phase of Labor – Definition:
The latent phase is part of the first stage of labor, which begins with onset of regular contractions and ends at 10 cm cervical dilation.
During the latent phase, there is:
Slow cervical dilation (from 0 to ~4–6 cm depending on criteria)
Effacement begins
Contractions may be mild to moderate and irregular or infrequent
This phase precedes the active phase, which is marked by more rapid cervical dilation and strong, regular contractions.
📖 Williams Obstetrics, 25th ed.:
“The latent phase is characterized by gradual cervical effacement and dilation, typically to 4–6 cm, often accompanied by mild and irregular contractions.”
📖 ACOG Practice Bulletin – Dystocia and Augmentation of Labor:
“Latent labor is defined as a period of labor with slow cervical change, generally ending at 5–6 cm dilation, with contractions that may not be regular.”
❌ Why the other options are incorrect:
“Strong, regular contractions with progressive dilation” → This defines the active phase.
“Between complete dilation and delivery” → This is the second stage of labor.
“Active pushing” → This is the expulsive phase of the second stage, not the latent phase.
