The Gemora states that the beds should be positioned between North and South.

One who fulfills this will merit 1) male children; 2)his wife will not miscarry.

It would seem from Rashi, and others say explicitly that the head of the bed should be to the North and the foot of the bed should be to the South.

Tosfos and other Rishonim explain that this is referring to a married couple during relations, for the Shechina is to the East and West and it is derogatory to engage in marital relations facing the direction of the Shechina.

Rabbeinu Yonah discusses the tefillah one should recite prior to relations; the tefillah then is easier than after the child is born.

Commentators on the Rosh discuss the scientific facts regarding the relationship between the position during relations and the gender of the child; the direction of the wind is a strong factor.

Shulchan Aruch rules that the correct position of the beds is from North to South, and even if his wife is not with him. (Does this apply to a single person?)

Mishna Berura cites Acharonim in the name of the Zohar that the correct position is East and West.

He rules, however, that we should follow our Gemora in this instance because the Vilna Gaon says that the correct interpretation of the Zohar is also like our Gemora.