The soft folds of the wall of the vagina allow it to adjust to the size of the penis. Vaginal intercourse can cause pregnancy. Touching the vulva with the penis can cause pregnancy, too. During sexual excitement the penis leaks semen that has thousands of sperm in it. Millions more sperm spurt out during ejaculation.
Pregnancy can happen if any sperm land on the vulva or inside the vagina.
A woman can become pregnant regardless of her position during vaginal intercourse. It doesn't matter if she has an orgasm or not. It doesn't matter if she is standing, sitting, or lying down. And it doesn't matter if the penis is withdrawn before ejaculation, or even if it's the first time she can still get pregnant. How sperm get from the vagina to the egg.