Physiology of Labor and Birth

The First Stage: Dilation

The first stage begins with the onset of regular contractions and ends when the cervix is fully dilated to 10 cm. This stage is divided into two phases:

1. Latent Phase (0–5 cm): The mother is typically alert, talkative, and able to follow directions. Contractions occur every 5–10 minutes.
2. Active Phase (6–10 cm): The mother becomes more serious, inwardly focused, and may find it difficult to follow directions. Contractions become more intense and frequent, occurring every 2–5 minutes.

The Second Stage: Delivery of the Neonate

This stage begins at full dilation and ends with the birth of the baby. It involves the birth sequence, including crowning (when the head is visible at the vaginal opening) and the expulsion of the fetus. During this stage, the mother may experience involuntary pushing and visible distension of the perineum.

The Third Stage: Delivery of the Placenta

The third stage begins after the birth of the neonate and ends with the delivery of the placenta. Signs that the placenta has separated from the uterine wall include a sudden gush of dark blood and the uterus becoming globular and firm.

The Fourth Stage: Maternal Stabilization

The final stage is the period of recovery, lasting typically 1–4 hours after placental delivery. Clinical focus shifts to assessing the mother's fundus, lochia (vaginal discharge), and perineum, while promoting skin-to-skin contact and breastfeeding.

Factors Influencing Labor: The Five P's

The progression and mechanics of labor are influenced by five key factors, known as the "Five P's":

1. Passageway: The maternal pelvis and soft tissues.
2. Passenger: The fetus, including its size, lie, attitude, presentation, and position.
3. Powers: The primary powers (uterine contractions) and secondary powers (maternal pushing).
4. Position: The physical position of the woman in labor.
5. Psyche: The psychological state of the mother, influenced by culture, anxiety, and previous experiences.

Clinical Monitoring and Interventions

Fetal and Uterine Assessment

Continuous Electronic Fetal Monitoring (CEFM) is often used to assess fetal well-being by tracking the Fetal Heart Rate (FHR) and uterine contractions.

• Normal FHR: A baseline between 110–160 bpm.
• Accelerations: An increase in FHR of at least 15 bpm for 15 seconds, indicating a healthy response.
• Decelerations:
  • Early: Associated with head compression; usually normal.
  • Late: Associated with uteroplacental insufficiency; requires immediate intervention.

Uterine activity is assessed by frequency, duration, and intensity. While intensity can be palpated (tip of nose = mild, chin = moderate, forehead = strong), the only way to quantitatively measure it is via an Intrauterine Pressure Catheter (IUPC).

Labor Support and Pain Management

Interventions aim to support the physiological demands of labor through hydration, position changes, and pain management.

• Non-pharmacologic: Breathing techniques, massage, hydrotherapy, and sacral counterpressure.
• Pharmacologic:
  • Analgesia: IV opioids to raise the pain threshold.
  • Anesthesia: Epidurals or spinal blocks to interrupt nerve impulses.

Warning: Epidural anesthesia can cause maternal hypotension. If systolic blood pressure drops below 100 mmHg or by 20% from baseline, nursing interventions like left lateral positioning and IV boluses are critical.