There are different kinds of fertility drugs to stimulate the ovaries. Each has advantages and disadvantages in terms of time, negative side effects, cost, and so on. Some are taken orally, others require shots. Still, others are delivered via a pump which is worn at the waist with a drip-feed entering a vein in the arm; this allows for small doses to be slowly and steadily absorbed.
Fertility drugs work in various ways, usually on the pituitary and/or hypothalamus. They stimulate the ovaries in the early part of the cycle to produce more and better follicles. They are very effective; 80 to 90 percent of women will ovulate regularly on the 13th or 14th day. Where the only cause of infertility is poor ovulation, there is a very good chance of pregnancy.
In fact, fertility drugs stimulate the ovaries so successfully that more than one egg is produced. This results in the problem of multiple births. There is a 10 to 25 percent chance of twins and triplets; with higher numbers, some of the embryos die, and/or are severely retarded. Though fertility drugs do involve multiple births, further research may soon reduce this risk.