I had asked what is the source for the segulah of having relations twice in order to have a boy. I first asked this in order to obtain a source to better ask this question.
The Gemorah says in Niddah 31b הרוצה לעשות כל בניו זכרים יבעול וישנה – One who wants to make all his children males should cohabit once and then repeat it.
In the answer to my question, Michoel so nicely brought the following explanation,
Rashi there explains that this comes in continuation to the previous statement in the Gemora that if the wife emits seed first the child conceived will be a male. By first arousing his wife's desire in the initial act, she will emit seed first the second time.
Howevver the Gemorah in Pesachim Daf 109b says ולא יעשה צרכיו תרי That a person shouldn't have relations twice as it is a problem of "zugos". Doing something in "pairs" could lead to some sort of sacana (danger).
Is there a stira between the 2 gemorahs? If so how can it be resolved?