CAUSES OF ONSET OF LABOUR & PHYSIOLOGY OF LABOUR

CAUSES OF ONSET OF LABOUR AND PHYSIOLOGY OF LABOUR

Labour is the process by which the fetus, placenta, and membranes are expelled through the birth canal. It typically occurs between 37–42 weeks of gestation. It is divided into stages and follows a physiological progression initiated by complex hormonal, mechanical, and biochemical factors.

CAUSES OF ONSET OF LABOUR

AYURVEDIC PERSPECTIVE

According to Ayurveda, the process of labour is a natural function governed by Prakr̥ti, Doṣas, Kala, and Karma. The Apāna Vāyu plays a key role in the expulsion of the fetus.

• ROLE OF APĀNA VĀYU
  Apāna Vāyu is the subtype of Vāta Dosha responsible for downward movements. During term, it stimulates the uterus for contraction and delivery.
  Reference:
  अधो गमनमूत्रपुरीषशुक्रार्तव गर्भनिष्क्रमण कर्माऽपानवायुः।
  (Aṣṭāṅga Hṛdaya Sūtrasthāna 12/4)

• ROLE OF TIME (KĀLA)
  Delivery occurs at the end of Garbha Māsa (ninth month) due to ripening of uterus and fetal maturity.
  Reference:
  गर्भः पूर्णे नवमासे प्रवर्तते।
  (Aṣṭāṅga Hṛdaya Śārīrasthāna 1/53)

• RIPENING OF THE FETUS (GARBHA PĀKA)
  The fetus is considered fully developed by the ninth month, ready for independent existence, prompting natural parturition.

• UTERINE EXPULSION DUE TO VĀTA UTKLEŚA
  Increase in Vāta during the ninth month and depletion of Kapha and Pitta leads to stimulation of uterine activity.

MODERN PERSPECTIVE

Labour is initiated by a series of maternal, fetal, and placental factors involving hormonal changes, uterine readiness, and mechanical stimulation.

HORMONAL FACTORS

• INCREASE IN ESTROGEN & DECREASE IN PROGESTERONE
  Estrogen promotes uterine contractility and oxytocin receptor formation. Progesterone withdrawal reduces uterine relaxation.

• RISE IN OXYTOCIN LEVELS
  Oxytocin, secreted by posterior pituitary, promotes uterine contractions.

• INCREASED PROSTAGLANDIN PRODUCTION
  Prostaglandins (mainly PGF2α and PGE2) cause cervical ripening and enhance uterine contractility.

• CORTISOL FROM FETAL ADRENAL GLAND
  Enhances lung maturation and initiates parturition by influencing placental estrogen synthesis.

MECHANICAL FACTORS

• STRETCHING OF THE UTERUS
  Overdistension of uterus (due to fetus and liquor) stimulates contractions via neuroendocrine reflexes.

• FERGUSON REFLEX
  Stretching of cervix stimulates oxytocin release, reinforcing uterine contractions in a positive feedback loop.

PHYSIOLOGY OF LABOUR

AYURVEDIC PERSPECTIVE

• STHĀNA OF APĀNA VĀYU – GARBHĀŚAYA (UTERUS)
  During labour, Apāna Vāyu exerts downward force to expel the fetus.

• MUKTI OF GARBHA – NATURE’S INTELLIGENCE
  It is said that labour is initiated by the ripening of the fetus who chooses the time of birth in accordance with past Karma.

  Reference:
  गर्भः कालेन पक्त्वा स्वकर्मानुगुणं शरीरेण निष्क्रामति।
  (Aṣṭāṅga Hṛdaya Śārīrasthāna 1/53)

• SUPPORTIVE ROLE OF PRAJA-STHĀPANĪYA MAHĀKAŚAYA DRAVYAS
  Use of herbs like Aśvagandhā, Śatāvarī, Bālā, and Jīvantī aid in strengthening the uterus and supporting labour.

MODERN PERSPECTIVE

PHASES OF LABOUR

• STAGE I – DILATATION STAGE

  • Begins with onset of regular contractions and ends with full cervical dilatation (10 cm).

  • Divided into:

    • Latent Phase (0–4 cm)

    • Active Phase (4–10 cm)

  • Contractions increase in strength and frequency.

  • Cervical effacement and dilatation occur.

• STAGE II – EXPULSION STAGE

  • From full dilatation to delivery of the baby.

  • Maternal pushing efforts (abdominal muscles and diaphragm) assist uterine contractions.

• STAGE III – PLACENTAL STAGE

  • From delivery of baby to expulsion of placenta and membranes.

  • Uterine contractions help in shearing off placenta from the uterine wall.

• STAGE IV – IMMEDIATE POSTPARTUM PERIOD (OBSERVATION STAGE)

  • First 1–2 hours after delivery.

  • Monitoring for hemorrhage, uterine firmness, vitals, and bonding.

MECHANISMS OF LABOUR (CARDINAL MOVEMENTS)

• Engagement

• Descent

• Flexion

• Internal rotation

• Extension

• External rotation (restitution)

• Expulsion

ROLE OF HORMONES DURING LABOUR