Labor (Parturition) - Obstetrics

Definition

Labor is the process of childbirth consisting of progressive uterine contractions that produce cervical effacement and dilation, leading to fetal expulsion and placental delivery. It is a continuous physiologic process divided into stages for clinical management. - The Developing Human: Clinically Oriented Embryology

True vs. False Labor

Before managing labor, the distinction between true and false labor must be made:

Feature	True Labor	False Labor (Braxton Hicks)
Contraction rhythm	Regular	Irregular
Intervals	Gradually shorten	Unchanged
Intensity	Gradually increases	Unchanged
Discomfort location	Back AND abdomen	Lower abdomen only
Effect of sedation	No relief	Usually relieved
Cervical dilation	Yes	No

False labor contractions do not produce cervical change and are treated with hydration and rest. - Tintinalli's Emergency Medicine

Stages of Labor

First Stage - Cervical Dilation

From the onset of regular uterine contractions to full cervical dilation (10 cm).

Divided into two phases:

Latent phase: Irregular, infrequent contractions. Cervix softens, effaces, and dilates slowly. This is the preparatory phase.
Active phase: Begins once the cervix reaches 3-4 cm dilation. Cervix dilates at:
- 1.2 cm/hour in nulliparous women
- 1.5 cm/hour in multiparous women

Average duration:

Primigravidas (first birth): ~12 hours total
Multigravidas: ~7 hours

Second Stage - Fetal Expulsion

From full dilation (10 cm) to delivery of the infant.

Mean duration: 54 minutes for nulliparous women, 20 minutes for multiparous women
The fetus descends through the cervix and vagina via the six cardinal movements

Third Stage - Placental Delivery

From delivery of the infant to expulsion of the placenta and membranes.

Usually lasts <10 minutes; 90% complete within 15 minutes
Active intervention typically not needed until >30 minutes
A placenta not expelled within 60 minutes is classified as retained placenta
After delivery, uterine retraction reduces the placental attachment area; a hematoma forms deep to the placenta and separates it from the uterine wall. Myometrial contractions constrict spiral arteries to prevent excessive bleeding.

(A fourth stage - the first 1-2 hours postpartum - is clinically recognized for monitoring maternal hemostasis.)

Cardinal Movements of Labor (Second Stage)

The fetal head negotiates the maternal pelvis through six movements in vertex presentation:

Engagement - the widest diameter of the fetal head passes below the pelvic inlet
Flexion - chin onto chest to present the smallest head diameter
Descent - downward progress through the birth canal
Internal rotation - head rotates to align with the anteroposterior pelvic outlet
Extension - head extends under the pubic symphysis at delivery
External rotation (restitution) - head rotates to align with fetal shoulders after delivery

Tintinalli's Emergency Medicine, Textbook of Family Medicine 9e

Cervical Assessment

Dilation: Diameter of the internal cervical os, 0 to 10 cm (full dilation)
Effacement: Thinning/shortening of the cervix, expressed as a percentage
Station: Level of the presenting fetal part relative to maternal ischial spines
- Above spines = negative station (-1, -2, -3)
- At spines = 0 station
- Below spines = positive station (+1, +2, +3)
- +3 station = fetal scalp visible at introitus (imminent delivery)

Rupture of Membranes

Spontaneous rupture occurs in active labor in most patients; ~8% rupture before labor onset
Confirmed by nitrazine paper (amniotic fluid pH 7.0-7.4 turns paper dark blue; vaginal pH 4.5-5.5 stays yellow)
Also confirmed by ferning (NaCl crystals on dried amniotic fluid under microscopy)
50% of women with premature rupture deliver within 5 hours; 95% within 28 hours

Fetal Heart Rate (FHR) Monitoring

Normal FHR: 120-160 bpm. Bradycardia: <110 bpm. Tachycardia: >160 bpm.

Key FHR patterns:

Fetal heart rate variability and uterine contraction patterns - showing normal variability, accelerations, flat tracing (possible hypoxia), variable decelerations, and late decelerations

A = Good variability (reassuring) | B = Accelerations (reassuring) | C = Poor/flat variability (possible fetal hypoxia) | D = Variable decelerations (cord compression) | E = Late decelerations (uteroplacental insufficiency)

Late decelerations - drops in FHR both during and >30 seconds after a contraction - are ominous and indicate uteroplacental insufficiency and fetal hypoxia.

Management of fetal distress:

Position mother in left lateral decubitus (reduces aortocaval compression)
IV hydration
Supplemental oxygen
Emergency obstetric consultation

Initial Clinical Evaluation

When a patient >20 weeks presents with signs of labor, obtain:

Maternal vital signs (BP, HR, RR, SpO2, temperature)
Fetal heart rate (Doppler US)
IV access, blood type, urinalysis
History: contraction onset/frequency, membrane status, vaginal bleeding, fetal movement, parity, prior delivery complications, prenatal care, estimated due date

Nagele's Rule: EDD = first day of last menstrual period + 9 months + 7 days

Fundal height: In cm from pubic symphysis to fundal top = gestational age in weeks (±2 weeks) after 20 weeks

Delivery Steps & Post-Delivery

Push only after full cervical dilation to avoid lacerations
Episiotomy is not routine; reserve for fetal distress, shoulder dystocia, or instrumental delivery
After delivery: keep infant warm, gentle stimulation; do not routinely suction nose/mouth (causes bradycardia)
Delayed cord clamping: at least 1-3 minutes after birth (increases neonatal iron stores)
Apgar scores at 1 and 5 minutes (color, tone, heart rate, respiratory effort, reflexes; score <7 requires action)

Sources:

The Developing Human: Clinically Oriented Embryology (9780323611541)
Tintinalli's Emergency Medicine: A Comprehensive Study (9781260019933)
Creasy & Resnik's Maternal-Fetal Medicine (9780323828499)
Textbook of Family Medicine, 9e (9780323239905)

This is a shared conversation. Sign in to Orris to start your own chat.