No study has confirmed that one position is more effective than any other in achieving pregnancy. In fact, sperm can be found in the cervical canal mere seconds after ejaculation, regardless of position. Of course, aiming for the deepest penetration and maximum cervical contact makes sense, but the optimal position varies because every woman's body is different.
And since sperm start swimming immediately after ejaculation, it isn't necessary for a woman to become a gymnast or a yoga master to make a baby. There may be a little advantage to lying around after intercourse to keep the sperm inside you, but there's absolutely no value in standing on your head, says Dr. Thatcher. So savor the mood however you please.