The Passage: Pelvic Shapes
The shape of the maternal pelvis significantly impacts the ease of delivery:
- Gynecoid: The most common (50%) and most favorable for vaginal birth.
- Anthropoid: Favorable (25%).
- Android: Funnel-shaped and not favorable (20%).
- Platypelloid: The least favorable (5%).
The Passenger: Fetal Characteristics
The fetal head is the largest and least compressible part of the passenger. Because the cranial bones are not yet fused, they undergo molding—an overlapping of bones to fit through the pelvis.
Fontanelles and Molding
Clinicians assess the fontanelles to determine fetal position and head compression:
- Anterior Fontanelle ("Soft Spot"): Diamond-shaped; stays open for 12–18 months.
- Posterior Fontanelle: Triangular; closes by 8–12 weeks.
It is also vital to distinguish between Caput Succedaneum (fluid under the scalp that crosses sutures and is benign) and Cephalohematoma (blood between the periosteum and bone that does not cross sutures).
Stages and Phases of Labor
Labor is divided into four distinct stages:
Stage 1: Cervical Dilation
This stage begins with the onset of labor and ends at 10 cm dilation. It is divided into three phases:
- Latent Phase: 0−3 cm dilation; contractions every 5−10 minutes; mother is often excited or talkative.
- Active Phase: 4−7 cm dilation; contractions every 2−5 minutes; mother becomes more inward-focused.
- Transitional Phase: 8−10 cm dilation; contractions every 1−2 minutes; mother may feel a loss of control.
Stage 2: Expulsion
Begins at 10 cm dilation and ends with the birth of the infant. Pushing may be spontaneous (natural urge) or directed (coached by a provider). Effective positions include lithotomy, semi-sitting, lateral, birthing stool, squatting, or kneeling.
Stage 3: Placental Delivery
Begins after the birth of the baby and ends with the delivery of the placenta. Signs of placental separation include a globular uterus, lengthening of the umbilical cord, and a sudden gush of blood.
Stage 4: Recovery
The first 1−4 hours after birth, focusing on maternal stability and bonding. Nurses must assess the fundus; a firm fundus is normal, but a boggy fundus indicates uterine atony and requires immediate fundal massage.
Fetal Assessment and Monitoring
Fetal well-being is primarily assessed via the Fetal Heart Rate (FHR). The normal baseline is 110−160 bpm.
Variability and Accelerations
Variability (the irregular "ups and downs" of the FHR line) is the most critical indicator of fetal oxygenation:
- Absent: 0 bpm
- Minimal: 1−5 bpm
- Moderate: 6−25 bpm (a positive, reassuring finding)
- Marked: >25 bpm
Accelerations (increases in FHR) are also a positive sign of fetal well-being.
Decelerations (VEAL CHOP)
Decelerations are drops in the FHR and are categorized using the VEAL CHOP mnemonic:
| Type | Cause | Clinical Meaning |
|---|
| Early | Vagal (Head Compression) | Benign; baby is descending |
| Late | Chord (Uteroplacental Insufficiency) | Ominous; risk of fetal acidosis |
| Variable | Cord (Umbilical Cord Compression) | May be ominous; often fixed by position change |
Emergency Intervention: Fetal Hypoxia
If the baby is not receiving enough oxygen, follow these steps in order:
- Change maternal position (lateral/side-lying).
- Turn off Oxytocin (Pitocin).
- Increase IV fluids.
- Administer Oxygen via mask.
- Contact the provider.
Clinical Interventions and Management
Rupture of Membranes (ROM)
The rupture of the amniotic sac can be spontaneous (SROM) or artificial (AROM). To confirm ROM, clinicians use a Nitrazine test (checking pH) or a Fern test (looking for a fern-like pattern under a microscope, which is the most reliable).
- Green fluid: Indicates meconium staining.
- Port-wine fluid: May indicate bleeding/abruption.
Pain Management
- Non-pharmacological: Hydrotherapy, ambulation, massage, breathing techniques, and position changes.
- Pharmacological (Narcotics): Such as Fentanyl. Caution: If administered within 3 hours of delivery, there is a risk of neonatal respiratory depression.
- Epidural: Blocks nerve impulses from $T10toS5$.
Nursing Alert: Epidurals can cause maternal hypotension. Always preload with an IV fluid bolus to prevent a drop in blood pressure.
Obstetric Emergencies
Cord Prolapse is a critical emergency where the umbilical cord slips ahead of the presenting part, causing compression.
- Signs: Severe variable decelerations immediately following ROM.
- Treatment: Place the mother in a knee-chest position, use a sterile finger to manually push the presenting part off the cord, and prepare for an emergency C-section.
Other emergencies include Placenta Previa, Placental Abruption, and Uterine Rupture.
Preterm Labor and Management
Birth occurring between 20–37 weeks is considered preterm.
- Fetal Fibronectin (FFN): A "glue" protein used to predict preterm labor; a negative result is a strong predictor that labor will not occur within 2 weeks.
- Management: Tocolytics (e.g., Indocin, Nifedipine) are used to slow contractions, and Betamethasone (steroids) is administered at 24–34 weeks to mature fetal lungs.
