Which method of contraception is the most effective? The Pearl index helps in the comparison and choice. The most favourable, i.e. lowest, indexes are characterised by long-term solutions: intrauterine systems and subcutaneous implants. What is more, their theoretical effectiveness is equal to their practical effectiveness. But one step at a time..
The effectiveness of hormonal contraception is due to the effect of inhibiting ovulation and changing the structure of cervical mucus and the mucous membrane in the uterus. This mechanism used in contraceptive pills should translate into 100 per cent effectiveness.
However, this is not the case. The absorption of the hormones - and therefore their metabolism, which influences their effectiveness - is affected by many factors. The most common is forgetting to take a tablet, but this is not the only risk factor. Even taking other medicines or eating disorders (vomiting, diarrhoea) can weaken or nullify the effect of the tablets.
Pregnancy in statistics
The effectiveness of contraception is measured by the Pearl index. This indicates, on the basis of the number of "slip-ups" by current users, how many women per hundred using a particular method become pregnant in a year. This rate is given as a number (e.g. 3 per 100) or as a percentage (3%).
When comparing Paerl indices for different forms of contraception, there are clear differences. Relying on periodic abstinence or condoms, we have to reckon in practice with a high (24 and 18 respectively) probability of unplanned pregnancy in the first year of use. When hormones are involved, the effectiveness increases significantly - solutions such as intrauterine systems or subcutaneous implants are practically as effective as female surgical sterilisation (Pearl index even at 0.05).
For other forms of hormones - e.g. pills/plasters/rings - the index ranges from around 0.3 to 9, with the actual contraceptive efficacy being most influenced by correct, regular use.
