sperms carrying Y and X chromozome are slightly different (because X is much larger than Y); woman’s opinions on her situation and her partner are reflected by her hormones; hormones might make woman’s reproductive system somewhat more friendly/hostile towards the desired/undesired sperms.
sperms with Y are smaller and faster, so they have a greater chance to fertilize the egg, but the male fetus also has a greater chance to be spontaneously aborted; stress (a predictor of bad future) makes the woman more likely to have a spontaneous abortion.
Some guesses at a possible mechanism:
sperms carrying Y and X chromozome are slightly different (because X is much larger than Y); woman’s opinions on her situation and her partner are reflected by her hormones; hormones might make woman’s reproductive system somewhat more friendly/hostile towards the desired/undesired sperms.
sperms with Y are smaller and faster, so they have a greater chance to fertilize the egg, but the male fetus also has a greater chance to be spontaneously aborted; stress (a predictor of bad future) makes the woman more likely to have a spontaneous abortion.