Illegitimate births

We very recently discovered that in 1788 my OHs 4x great grandfather was detained in a House of Correction for six weeks, only being released on the very day of his marriage.
Records state that his wife-to-be had sworn an oath that he was the father of the baby she was carrying, and that he was detained due to fears that he might otherwise abscond.

Yes, I have found the same.

I've found what seems to be a disproportionate number of eldest daughters who have had an illegitimate child.
I've come to the conclusion that their parents raised them in ignorance of sexual matters, but younger sisters tended to learn from their big sister's mistake.

It took me a long time to find anything other than childhood census records for one relative (the eldest child in the family!) and there was no sign of her after marriageable age either.
I eventually worked out that she had been born a couple of years before her mother married (he was not the father) but they tried to hide this by lying about her legal surname on the censuses, and gave a later date of birth too.
No wonder I hadn't been able to find a birth record or a marriage record for her, as they were in her mother's maiden name, not her married name!

I find it all fascinating.