Normal menstruation

  • During the reproductive age, each woman undergoes series of changes at the ovaries and the lining of the womb in preparation for the possibility of pregnancy. These changes are coordinated and if the woman is not pregnant, things repeat again every month. This is called the menstrual cycle.
  • At the ovarian level, a hormone called oestrogen is produced by the ovaries and it makes the lining of the womb grow. This first half of the menstrual cycle is called the ‘follicular’ (refers to the ovary) or ‘proliferative’ (refers to the lining of the womb) phase. An egg is then released from one of the two ovaries and this is called ‘ovulation’. The egg is collected by the fallopian tube where it can meet the sperm for fertilization. After ovulation, the involved ovary produces another hormone called progesterone. This hormone acts on the lining of the womb leading to glandular changes, which is ideal for implantation of the embryo if fertilization happens. The second half of the menstrual cycle is called the ‘luteal’ or ‘secretary’ phase.
  • If pregnancy occurs, the ovary continues to produce progesterone and a placenta is formed. If pregnancy does not take place, the ovary stops producing the hormones at the end of the cycle. The lining of the womb is then shed and it is the menstruation. The cycle will then repeat itself.

The criteria for normal menstrual cycles:

  • Menarche (first period): 12-13 years of age, usually 2-3 years after breast budding has occurred (thelarche)
  1. (i) Should see doctor if still no period by 15 years of age or 3 years after thelache
  2. (ii) Menstrual cycles are often irregular during adolescence. However, by 3rd year after menarche, 60-80% of menstrual cycles are normal
  • Cycle length (duration between the first day one cycle to another): 24-38 days
  • Regularity: some variation in the cycle length is expected for an individual
  1. (i) Considered ‘regular period’ if the difference between the shortest and longest cycle length is </=9 day
  • Duration: 2 to </=8 days
  • Menopause: usually between 45-55 years of age, average in Hong Kong- 51 years old.
    Early menopause: <45 years of age; Premature menopause: < 40 years of age


This article is contributed by Dr. T.N. Danny Leung
updated on 18.11.2020