How effective is the withdrawal technique …………getting pregnant?

Don't ever fall for this one, baby. It cuts you both ways.
If withdrawal is done properly, you are left a bit unsatisfied. Don’t you realize how important it is that the ‘material’ be emptied deep inside you? Men, too, find full sexual satisfaction only when they are able to ejaculate deep inside you.
On the other hand, if withdrawal is not proper, you risk getting pregnant. So don't risk it.
Insist on a condom or use contraceptives.