Measures to be taken to avoid pregnancy after intercourse

You take measures to avoid pregnancy BEFORE intercourse. It's not something that is just an afterthought.

There is something called a "morning after pill". I believe it can be purchased from a pharmacy without a prescription but am not sure - you might need a prescription. It needs to be taken within a short time of intercourse - a day or two I believe (a doctor of pharmacist should be consulted). It works by preventing implantation of the fertilized egg.

The morning after pill is for emergency use, if you use it too often, it has serious side effects that are possible.

You need to first consider should you be having sex, are you ready for a baby, since no birth control is 100 percent.

The women needs to be on birth control pills and the pills be taken correctly.
They need to also always use a condom.

Even then pregnancy is possible.