The most likely time for fertilisation to occur is around ovulation which is roughly half way through the menstrual cycle (day 14 although this varies from person to person). There are kits you can get to test for fertility which look for an increase in hormones and there is on average a 0.3 degrees increase in body temperature around the time of ovulation.

Sperm are viable for up to 6 days after ejaculation once they are inside the female.

Woman underneath with a small cushion below her pelvis to raise the hips slightly.

This is very rare and yet it is technically possible as sperm may come into contact with the vagina in other ways. Also IVF can lead to fertilisation without intercourse.

Fertilisation can occur the first time you have sex. However it does require more than one sperm in order to create a path through the outer layers of the egg to enable the successful sperm to penetrate the egg.

The Morning After Pill (which is the common emergency contraceptive pill), is in effect named wrongly. It can work up to 72 hours (3 days) after sex however the earlier you take it the more effective it will be.