Is this bollocks about boy sperm and girl sperm?

[Moancup]

I was browsing a pregnancy for dads book and it included the claim that only girl sperm can survive to fertilise the egg if you have sex two or three days before ovulation.

Surely it’s bollocks to be that definitive?

Now I’ve heard frequently that male sperm are faster and female sperm are slower but hardier. But given how the fertile window works, surely there would be a massive surplus of women in the population if boys were only conceived from sex right before ovulation?

I personally think it’s bollocks but have no idea if there’s any scientific evidence tbh. I have 2 boys and am pregnant with a girl. When ttc I used ovulation sticks and they were all conceived by having sex either the day of or the day before ovulation (didn’t care what sex, just wanted a baby so tried to do it at the best time to conceive!)

I think that's the idea behind the shettles theory, which has been debunked. If there was any reliable way to sway gender I'm pretty sure people would have figured it out by now - especially in times / places where one sex is/was prized above another.

We only DTD day before ovulation, ovulation day and the day after, and NIPT test says I'm having a girl 🤷‍♀️