Engaging Transverse Diameter in Normal Labour
In the mechanism of normal labour, the process of engagement occurs when the largest transverse diameter of the fetal presenting part enters the pelvic inlet.
The engaging transverse diameter refers specifically to the widest diameter of the fetal head lying in the transverse or oblique diameter of the pelvic inlet.
Identifying the Correct Diameter
The fetal skull has several diameters. For engagement into the pelvic inlet, the transverse dimensions are critical:
- The Biparietal diameter is the distance between the two parietal eminences. This is typically the widest transverse diameter of the fetal head.
- The Bimastoid diameter is smaller than the biparietal diameter.
- Diameters like the Suboccipitobregmatic and Suboccipitofrontal are measured longitudinally (front to back), not transversely.
Therefore, the Biparietal diameter, measuring approximately $9.5$ cm, is the key transverse diameter that must engage for the head to descend further during normal labour.
This diameter is crucial for fitting through the pelvic inlet.
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?
