Positions for intercourse vary. The commonest sexual position is the so-called missionary position in which the woman lies on her back with her legs bent up and the man lies on top of her. Penetration is generally deepest in this position.
Other commonly used positions include the reverse of the missionary position with the woman on top of the man, the woman sitting on top of the man (either facing towards him or away), the man entering the vagina from behind while the woman kneels on all fours and lying side by side, either face to face or the woman’s back to the man.
Numerous other positions are used regularly by many couples, and as can be attested by the Kama Sutra, the Indians of 3000 years ago were adept at conjuring up all sorts of gymnastic combinations and permutations of male and female anatomy that managed in some way to bring the penis into the vagina.
It does not matter which position is used for sex as far as becoming pregnant is concerned. The couple should use the position that suits their needs and desires most.