What constitutes a delayed menstrual period (menstruation)?

From the Guidelines

A late period is typically considered when menstruation is delayed by more than 7 days from when it was expected, based on your regular cycle, as a health-care provider can be reasonably certain that a woman is not pregnant if she has no symptoms or signs of pregnancy and meets any one of the criteria outlined in the U.S. selected practice recommendations for contraceptive use, 2013 1. When determining if a period is late, it's essential to consider the individual's normal menstrual pattern, as what constitutes "late" can vary significantly from person to person.

• If you typically have a 28-day cycle, a period would be considered late if it hasn't started by day 35.
• However, the most common cause of a late period is pregnancy, so taking a pregnancy test is often recommended if you're sexually active, as the sensitivity of a pregnancy test is defined as the concentration of human chorionic gonadotropin (hCG) at which 95% of tests are positive, and most qualitative pregnancy tests approved by the U.S. Food and Drug Administration (FDA) report a sensitivity of 20–25 mIU/mL in urine 1. Other potential causes of a late period include:
• Stress
• Significant weight changes
• Excessive exercise
• Hormonal imbalances
• Polycystic ovary syndrome (PCOS)
• Thyroid disorders
• Perimenopause
• Certain medications If your period is consistently late or irregular, or if you miss multiple periods, it's advisable to consult with a healthcare provider to determine the underlying cause, as they may recommend blood tests or ultrasound imaging to check hormone levels and rule out any medical conditions that might be affecting your menstrual cycle, and provide reassurance if amenorrhea does not require any medical treatment 1.

From the FDA Drug Label

When you do not produce enough progesterone, menstrual irregularities can occur. Progesterone capsules are used for the treatment of secondary amenorrhea (absence of menstrual periods in women who have previously had a menstrual period) due to a decrease in progesterone

A late period is not explicitly defined in the provided drug label. However, it can be inferred that a late period may be related to menstrual irregularities caused by a decrease in progesterone.

• Secondary amenorrhea is defined as the absence of menstrual periods in women who have previously had a menstrual period, which may be due to a decrease in progesterone.
• The label does not provide a specific time frame for what constitutes a late period 2.

From the Research

Definition of a Late Period

A late period is typically defined as a delay in the onset of menstruation beyond the expected date.

Factors Influencing Menstrual Cycle

Several factors can influence the menstrual cycle, including:

• Hormonal changes
• Contraceptive use 3, 4, 5
• Menstrual bleeding changes

Contraceptive Methods and Menstrual Cycle

Different contraceptive methods can affect the menstrual cycle in various ways:

• Oral contraceptive pills can regulate menstrual cycles, but may also cause changes in menstrual bleeding patterns 3, 4
• Progestin-only pills can cause irregular bleeding and spotting 4, 5
• Intrauterine devices and subdermal implants can also affect menstrual bleeding patterns 3, 5

Menstrual Cycle Changes During Perimenopause

During perimenopause, women may experience changes in their menstrual cycle, including:

• Irregular bleeding patterns
• Increased symptoms such as vasomotor symptoms, menorrhagia, and mastalgia 6
• Hormonal changes, including increased estrogen levels and decreased progesterone levels 6