Climate change can indirectly impact menstruation by affecting access to clean water and sanitation facilities, which can lead to increased rates of infection and illness that can affect menstrual cycles. Additionally, climate change can cause extreme weather events that can disrupt supply chains and affect the availability of menstrual products.

After giving birth, it is common for women to experience changes in their menstrual cycle. The return of periods can vary depending on individual factors such as breastfeeding and overall health. Breastfeeding can delay the return of periods because it affects the production of hormones that regulate the menstrual cycle. This is due to the hormone prolactin, which is produced during breastfeeding and can suppress ovulation.

For women who are not breastfeeding, periods may return as early as six weeks after delivery, although it can take several months for the menstrual cycle to regulate and become predictable again. It is important to note that the first few periods after delivery may be heavier or longer than usual due to hormonal changes and the body's process of shedding the uterine lining that built up during pregnancy.

It is important to discuss any concerns or questions about changes in periods after delivery with a healthcare provider, as they can provide personalized advice and guidance based on individual health history and circumstances

During pregnancy, many changes occur in a woman's body, including changes to the menstrual cycle. In most cases, periods will stop completely during pregnancy. This is because the hormonal changes that occur during pregnancy prevent ovulation, which is the release of an egg from the ovary. Without ovulation, there is no need for menstruation. Some women may experience light bleeding or spotting during early pregnancy, which is often called implantation bleeding, and is usually lighter and shorter than a regular period. However, any bleeding during pregnancy should be discussed with a healthcare provider to rule out any potential complications. After giving birth, it may take several weeks or months for periods to return, as the body goes through a process of healing and adjusting after pregnancy.

The first day of the menstrual cycle is considered to be the first day of menstrual bleeding. This is typically referred to as "day one" of the menstrual cycle. The length of the menstrual cycle is measured from the first day of bleeding to the first day of the next menstrual period.