**Core Concept**
The menstrual cycle is regulated by a complex interplay of hormonal changes, primarily involving the hypothalamic-pituitary-ovarian axis. After childbirth, the body undergoes significant hormonal shifts, affecting the resumption of menstruation.

**Why the Correct Answer is Right**
The first menstrual period, also known as menstruation or menses, typically resumes 6-8 weeks after delivery in non-breastfeeding women. This delay is due to the inhibitory effect of prolactin, which is elevated during lactation, on the hypothalamic-pituitary-ovarian axis. As long as prolactin levels remain high, the body suppresses the production of gonadotropin-releasing hormone (GnRH), leading to decreased follicle-stimulating hormone (FSH) and luteinizing hormone (LH) secretion. When prolactin levels decrease, typically after cessation of breastfeeding, the hypothalamic-pituitary-ovarian axis is reactivated, and menstruation resumes.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the typical timeframe for resumption of menstruation in non-breastfeeding women is not within 2 weeks after delivery.
**Option B:** This option is incorrect because the resumption of menstruation is not typically associated with the initiation of breastfeeding.
**Option C:** This option is incorrect because the timeframe for resumption of menstruation is not within 12 weeks after delivery.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the resumption of menstruation after childbirth can be influenced by various factors, including the duration of breastfeeding, the presence of any underlying medical conditions, and the overall health status of the individual. A healthcare provider should be consulted to determine the underlying cause of amenorrhea (absence of menstruation) in a postpartum woman.

**Correct Answer:** D. 6-8 weeks.