The simple answer for this will have to be "most likely nothing, but possibly a lot" so i suggest we go through the detailed answer. No short cuts this time!
The main reason for writing this detailed answer is because often a girl such as this may be told simply that it could be a problem with genetics or with hormones. That can scare her un-necessarily. Seeing a doctor is a good idea but being scared by the internet is not!
There could be dozens of reasons why a 16 year old may have not had her first period but thankfully the most common reason is a unexplained delay in menarche. You will be pleased to know that this has no bearing on health or problems in the future, especially fertility. Basically just a matter of chance that your periods have not started "in time".
If you are a student of mathematics or statistics you know that in a "normal distribution curve" or Bell's Curve, around 97% of the subjects will fall within two "standard deviations". The age of 16 is the top end of this range of two standard deviations. It doesn’t mean that somebody who begins her menstrual period six months later, is abnormal. Just less common than expected.
However since menstruation is so closely linked with fertility, it is obviously a cause for concern more for the parents than for the girl herself. I will list the five main groups of causes of primary amenorrhoea(absence of periods) which are most likely..
The point to note in the above list is if you have any of these problems you should not worry, because most can be resolved quite easily.
answered Jun 26 '13 at 02:13
may be some genetic abnormality
answered Feb 26 '13 at 22:17
One or more of the following are the common causes for primary amenorrhea.
1. Structural problems
2. Hormonal imbalance arising from improper functioning of pituitary gland and ovaries either due to birth defect or some disease like Craniopharyngioma (non cancerous pituitary tumor), Cystic fibrosis
3. Anorexia (extremely low body fat) or excessive and rigorous exercise
There could be other reasons too than the ones mentioned above. An obstetrician or gynecologist would perform several tests to narrow down to the probable cause for primary amenorrhea in a patient.
answered Mar 03 '13 at 07:56