Now, about fertility ~ did you see the trouble Abraham got into when he didn't "test first"? Yup. God had to provide him some direction to get an early heir!
That one event can be taken as a COMMANDMENT if you want. I am just guessing you don't want ~ but there it is.
Not to worry, I've met snakehandlers in my time ~ and they've told me that unless I take up the serpents I'm going to go to Hell, and you can't hardly beat that.
Still, the marriage to pregnant brides is hardly a myth ~ it's been going on among the peasantry for thousands of years.
Isaac took one wife. Rebekah.
Abraham was a monogamist until, at the urging of his wife, he took a concubine. He later sends that concubine and their son away and does not take a wife until Sarah dies.
Jacob takes two wives and two concubines; he was a polygamist, and his polygamy led to much grief, jealousy and pain.
In none of their cases is it recorded that they “tested” out their wives prior to marriage to determine their fertility.
David and Solomon took many wives, but their examples are not held up for emulation. Solomon’s wives turn him away from the Lord, and David arranges for the husband of a married woman he takes to his bed to be murdered.
There is no “commandment” for testing for fertility anywhere in Scripture.
None of the people mentioned “tested first” for the purpose of determining fertility, and you have yet to establish any ancient people who had the custom of “testing” a young woman’s fertility before marrying her.
You have made claims without backing them up, and you have distorted what Scripture records about the examples you have held up.
Abraham got into trouble by not trusting God to provide the promised child. He tested the fertility of Hagar, and now we have Mideast mess.