Parturition means the birth of the baby at the end of about 9 months of pregnancy. It is controlled by a neuroendocrine mechanism: signals from the fully grown foetus and the placenta start mild uterine contractions called the foetal ejection reflex, this makes the mother's pituitary release oxytocin, and oxytocin causes stronger and stronger uterine contractions to push the baby out. Memory hook: "Foetus signals, Oxytocin pushes" - the baby itself sends the first signal to be born.
The foetus and placenta send the first signals, starting mild contractions (foetal ejection reflex). This releases oxytocin from the posterior pituitary, which causes stronger uterine contractions. The contractions feed back to release more oxytocin (positive feedback) until the baby is delivered.
Your doubts, answered
What triggers parturition? Where does the first signal come from?
The first signals come from the fully developed foetus and the placenta, NOT from the mother. These signals cause mild uterine contractions called the foetal ejection reflex. This is a favourite NEET point: the baby starts its own birth. The signal then triggers oxytocin release from the mother's pituitary.
Which hormone causes the foetal ejection reflex and how?
Oxytocin. After the foetal ejection reflex begins, oxytocin is released from the mother's posterior pituitary. Oxytocin acts on the smooth muscle of the uterus and causes vigorous (strong) contractions. This is a positive feedback loop: more contraction leads to more oxytocin, which leads to still stronger contraction, until the baby is delivered.
Is the foetal ejection reflex the same as the milk ejection reflex?
No, but the SAME hormone controls both, and NEET tests this. Oxytocin causes the foetal ejection reflex (uterine contraction to push the baby out during parturition) AND the milk ejection reflex (milk let-down from the mammary glands during lactation). Same hormone, two different jobs.
Is prolactin part of parturition? Why is this a common mistake?
No. Prolactin controls milk SYNTHESIS (making milk) during lactation, not the start of labour. NEET 2021 asked which is NOT a component of initiation of parturition, and the answer was 'Release of Prolactin'. Remember: parturition uses oxytocin, prostaglandins, and a rising estrogen/progesterone ratio - prolactin is for milk, not for birth.
Where is oxytocin released from during childbirth?
Oxytocin is released from the posterior pituitary (neurohypophysis) of the mother. Important: oxytocin is SYNTHESISED by the hypothalamus but STORED and RELEASED by the posterior pituitary. NEET often traps students who think the posterior pituitary makes it.
What is the role of relaxin in birth?
Relaxin is secreted by the ovary (corpus luteum) in the later phase of pregnancy. It relaxes the pelvic ligaments and softens the cervix so the birth canal can widen for delivery. Relaxin does NOT trigger the foetal ejection reflex; oxytocin does that.
⚠️ The NEET trap ✗ Prolactin is one of the hormones that initiates parturition. ✓ Prolactin is NOT a component of initiation of parturition. The components are oxytocin release, synthesis of prostaglandins, and an increase in the estrogen/progesterone ratio. Prolactin only controls milk synthesis in lactation. 🧠 Prolactin = PRODUCE milk. Oxytocin = PUSH the baby. If a question lists hormones for STARTING labour and prolactin appears, prolactin is the odd one out.
Real NEET questions
NEET 2021
Which of these is not an important component of initiation of parturition in humans?
A · Release of Oxytocin
B · Release of Prolactin ✓
C · Increase in estrogen and progesterone ratio
D · Synthesis of prostaglandins
Solution: Parturition is started by a neuroendocrine mechanism: the foetal ejection reflex triggers oxytocin release, oxytocin causes strong uterine contractions, and prostaglandins with a rising estrogen/progesterone ratio support the process. Prolactin controls milk synthesis in lactation, not the start of labour, so it is NOT a component of initiation of parturition.
NEET 2019 (Odisha)
Which of the following hormones is responsible for both the milk ejection reflex and the foetal ejection reflex?
A · Estrogen
B · Prolactin
C · Oxytocin ✓
D · Relaxin
Solution: Oxytocin acts on smooth muscle. During parturition it drives the foetal ejection reflex (vigorous uterine contraction to expel the baby), and during lactation it drives the milk ejection (let-down) reflex from the mammary glands. Both reflexes are controlled by the same hormone, oxytocin.
Solved Human Reproduction NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Parturition is childbirth - the delivery of the baby out of the mother's uterus at the end of pregnancy (gestation), which lasts about 9 months in humans.
What is the foetal ejection reflex?
It is the set of mild uterine contractions that start when signals come from the fully developed foetus and the placenta. This reflex triggers oxytocin release, which then causes stronger contractions to push the baby out.
Which hormones are involved in parturition?
Oxytocin (drives strong uterine contractions), prostaglandins, and a rising estrogen to progesterone ratio. Relaxin softens the pelvic ligaments and cervix. Prolactin is NOT involved in starting labour.
Why is parturition called a positive feedback mechanism?
Because uterine contraction causes more oxytocin release, and more oxytocin causes even stronger contraction. This cycle keeps building until the baby is delivered, then it stops.
What is the gestation period in humans?
About 9 months. Vigorous uterine contractions at the end of this period cause the expulsion of the foetus, which is parturition.
