High Fertility can have a number of different meanings. When it is used in reference to a person it usually means the time when a woman can get pregnant the easiest. A woman has around 7 days of high fertility in her periodic cycle. This is when the egg is in the uterus and can therefore get fertilised after sexual intercourse. It is recommended that a woman uses contraception during her high fertility unless she wants to get pregnant. High fertility ends when the person in question ovulates and the egg leaves the uterus. A woman's fertility can depend on her diet, environment and other factors such as medication. High fertility can also refer to a country's fertility rate which is the number of children on average a woman has in her lifetime. A higher fertility rate means that more children are born in the given country every year. If it is higher than the replacement rate (which is usually around 2.1, however it is higher in developing countries due to a higher mortality rate), then the population will increase, however if it is lower than the replacement rate then the population will decline. Developing countries have higher fertility rates due to a number of factors including the aforementioned high mortality rates, lack of education and lack of available contraception just to name a few, leading to an increasing population. More developed countries on the other hand usually have lower fertility rates due to a better understanding and better availability of contraception, later marriages and cultural factors such as women pursuing a career instead of raising children and staying at home.
It just means these are days you have a high chance of getting pregnant because you are very fertile.
High Fertility means there is possibility of getting more pregnancy