Final answer:
Cervical dilation and effacement are the best indicators of true labor. These signs demonstrate the positive feedback loop of labor, where contractions become more potent and regular, leading to the progression of childbirth. Other signs like 'bloody show' and fetal descent are indicative but not as definitive. The correct option is B.
Step-by-step explanation:
The best indicator of true labor is cervical dilation and effacement. True labor is characterized by a positive feedback loop, where uterine contractions stretch the cervix, causing it to dilate (widen) and efface (thin out). This dilation promotes the secretion of oxytocin, which further stimulates more intense uterine contractions. As labor progresses, these contractions become stronger and more frequent, which is essential for the progression of labor and eventual delivery of the baby.
A so-called "bloody show," which is the expulsion of the mucus plug from the cervical canal, is a common sign that labor will be short. However, it's not necessarily an indicator of true labor, but rather a pre-labor sign. On the other hand, fetal descent into the pelvic inlet and uterine contractions at regular intervals are part of the labor process but are not as definitive of true labor as cervical change.
During the first stage of childbirth, the cervical canal must dilate to about 10 cm to allow the baby's head to pass through. Without adequate dilation and effacement, even regular uterine contractions do not indicate that the labor is effectively progressing towards delivery.