Final answer:
The correct answer to the period after childbirth is b) puerperium, which is the time from the end of childbirth until the mother's body returns to a non-pregnant state, lasting about six weeks.
Step-by-step explanation:
The period after childbirth is referred to as the puerperium. This phase lasts from the end of childbirth until about six weeks after, as the mother's body, particularly her reproductive system, returns to a non-pregnant state. The linea nigra is a dark line that forms during pregnancy and persists for some time after childbirth, but it is not the term for the period after childbirth. The afterbirth is specifically the delivery of the placenta, which occurs after the baby is born. Lastly, a fontanel is the soft spot on a baby's head where the skull bones have not yet fused.
It is important to note that while the neonatal period occurs in the newborn, the puerperium focuses on the mother's recovery, along with physiological changes such as the cessation of lochia (postpartum vaginal discharge) and the uterus returning to its pre-pregnancy size.