If hundred eligible couples decided to have a family, they should have intercourse especially at the time of ovulation. This is called fertile period. For example if a woman is having a 28 day regular cycle she will ovulate on day 14 according to Knause, and Ogino. Latter half of the menstrual cycle is regular and if woman is, having 35 days regular cycle her will ovulate on day 21. Similarly, if the woman is having 21-day regular cycle she will ovulate on day 7 of the cycle. If the woman is having irregular cycles in situations such as polycystic ovarian disease or obesity or underweight in excise induced, psychological condition such as crash dieting causing anorexia nervosa.
So if 100 eligible couples have intercourse in a month only about 10-20% will conceive. If they have, intercourse regularly for one year 80% will conceive. If they go on for 2 years 90% will conceive leaving 10% childless or infertile or sub fertile.
At the time of ovulation if a woman feels secretions in her genital area and try to stretch the secretion between thumb and index finger she will be able to stretch it to about 5cm. This shows that she is about to ovulate. Occasionally she may have a little bit of brownish or blood with this secretions. This is called mid-cycle spotting. If the woman wants to conceive, she should have intercourse at this time. If she wants to avoid, she can use natural or artificial method of contraception such as condoms at this time. A man called Biling popularized this method.
Ideal age a woman should conceive is between 25-30. After 35, her nucleus in the ovum or egg gets defragmented and she will conceive, abort, or end up with a chromosomally abnormal baby such as Downs Syndrome.
If the woman is above 35 if she does not conceive after 6 months of regular intercourse, she should seek specialist fertility advice.