Presently 5 to 10 per cent of reproductive-age women suffer from infertility because of PCOS.

Women suffering from PCOS usually have excessive levels of a hormone called androgen, infrequent periods, with development of small cysts on the ovaries and have trouble conceiving.

Clomiphene citrate known to stimulate ovulation has been used as the standard treatment for PCOS. But researchers say it has certain drawbacks and the success rate is no more than 22 per cent. It also causes some annoying side effects like hot flashes and frequent mood swings.

Letrozole is another drug which blocks estrogen production. It also increases the rate of pregnancy in women with PCOS , these results have appeared in the current issue of the New England Journal of Medicine by Dr. Richard Legro, professor of obstetrics and gynecology and lead author of the study.

In order to compare the effectiveness of these two drugs, scientists studied 750 infertile women with PCOS between 18 and 40 years old who wanted to get pregnant.

Women were randomly given clomiphene or letrozole and took the medications for up to five cycles, with increasing dosage at each cycle.

The group of women who took letrozole had a higher rate of live births ( 27.5 per cent) than the women who received clomiphene (19.1 per cent). Also ovulation rates were significantly higher with letrozole each month.

Fewer twin pregnancies occurred in the women who took letrozole (3.9 per cent) and 6.9 per cent on clomiphene. Clomiphene taking women experienced significantly higher incidence of hot flashes while letrozole caused significantly higher incidence of fatigue and dizziness. Birth defects were rare and rates were similar between the two medications, comparable to those from studies of women who conceive without treatment.

Further investigation is required with a larger number of infants to clarify the safety of letrozole.