Hebrews 13:4 Marriage is honourable in all, and the bed undefiled: but whoremongers and adulterers God will judge.
If a person has sex before they are married the bed is defiled. Marriage and the intimate relationship that comes with marriage is blessed when the couple agrees to become one flesh and united in Matrimony.
Many people have sex before they are wed and sometimes pregnancy occurs. Many times for whatever reason people "break up" and the marriage never happens.
A man should save himself for his wife and a woman should save herself for her husband. A couple is not saving themselves if they have sex before marriage.
Fornication is a sin and unless a person is married they are commiting fornication if they engage in a sexual relationship.
The bible calls children born out of wedlock "illegitimate" although the real word starts with a b and ends with an d in the King James Bible.
We have become very "politically correct" even in the bible.
Women were considered "whores" in the Old Testament if they had sex outside of marriage and they didn't necessarily have to be in business to be called one.
The brothers of Tamar slew the Hivites because Shechem had sex with their sister before marriage. The reason is because she was treated as a whore.
Genesis 34:31 And they said, Should he deal with our sister as with an harlot?
The bible is very clear that sex outside of marriage is forbidden by God.
In the OT there are examples that as soon as a man and a woman had a sexual relationship that meant that they had become man and wife.
Genesis 24:67 And Isaac brought her into his mother Sarah's tent, and took Rebekah, and she became his wife; and he loved her: and Isaac was comforted after his mother's death.
Having sex before marriage is "putting the cart before the horse".
I hope this has been helpful.