THE average age at first menstruation is 12.4 years witharangeofagenineto 16. There are a number of factors that influence this, but one of the strongest ones is weight. The critical body weight is 46 to 47kg. Body fat should — at a minimum — be 17pc for menstruation to start and 22pc to maintain it.
It takes on average one to three years for the complex hormone cycle to mature once menstruation commences. The average menstrual period lasts from three to seven days and occurs at a cycle of between 21 and 35 days. The range of normal varies greatly and simply understanding this may be enough to put your mind at rest.
In order for menstruation to occur the body must be progressing through the various stages of puberty.
Primary amenorrhoea is defined as the absence of menstruation by age 16. The first step in deciding the cause is to check how puberty is progressing. If your daughter is showing all other signs of puberty, namely a change in body shape, the growth of hair in the pubic area and under her arms and normal breast development then this is reassuring. You describe a thin active girl and it sounds to me that this may indeed be the cause of delayed menstruation.
Psychological distress can also delay menstruation. You say your daughter is happy and active, so this doesn’t seem to be the cause. Anxiety and stress are, however, very common in teens today and it is important to be vigilant.
As she is nearly 16 I do feel further investigation is warranted. Some simple blood tests can rule out hormonal causes such as pituitary problems or polycystic ovarian syndrome. Your doctor can do a general examination to ensure no other causes are suspected. An ultrasound can help rule out abnormalities of the womb or ovaries.
If the cause is felt to be down to