Consider the following statements regarding the cause for onset of labour : Statement 1 : Alteration in estrogen-progesterone ratio results in prostaglandin synthesis and onset of labour. Statement 2 : Decreased fetal production of dehydroepiandrosterone sulfate (DHEA-S) and cortisol inhibits the conversion of fetal pregnenolone to progesterone. Which one of the following is correct with respect to the above statements?
Statement 1 is true but Statement 2 is false
The correct answer is Statement 1 is true but Statement 2 is false. Statement 1 states the functional progesterone-withdrawal theory: near term a rise in the oestrogen-to-progesterone ratio ends myometrial quiescence, increasing gap junctions (connexin-43), oxytocin receptors and calcium channels, and activating decidual phospholipase A2, which liberates arachidonic acid and generates prostaglandins E2 and F2-alpha, which ripen the cervix and drive coordinated contractions.
Statement 2 is false because it reverses the physiology. Near term, maturation of the fetal hypothalamo-pituitary-adrenal axis increases adrenal DHEA-S and cortisol. DHEA-S is aromatised by the placenta to oestriol, raising the oestrogen-progesterone ratio, while cortisol up-regulates placental CRH and prostaglandins. The fetal steroid surge therefore promotes labour, so both options calling statement 2 true, and the option calling statement 1 false, are wrong.
Key point: The sequence is fetal HPA activation, rising oestrogen-progesterone ratio, prostaglandin release, oxytocin receptor up-regulation, contraction.
Important Questions from Normal Labour
Which of the following features are correct regarding onset of true labour?
1. Regular uterine contractions
2. Progressive cervical dilation and effacement
3. Presence of show
4. Labour and delivery are synonymous
Select the answer using the code given below.
- According to the WHO Intrapartum Care Guidelines, 2018, the active phase of labour starts from what dilation of cervix?
Onset of labour is initiated by which of the following?
1. Uterine distension
2. Increased CRH and ACTH from foetal hypothalamic-pituitary- adrenal axis
3. Increased level of progesterone immediately before labour
4. Increased synthesis of myometrial receptors for oxytocin due to effect of oestrogen
Select the correct answer using the code given below.
- The normal rate of dilatation of the cervix in a primigravida in the active phase of labor is
- Regarding the phenomenon of 'lightening' in primigravida at term pregnancy, which one of the following statements is correct?
