TLDR: That translation takes a Hebrew passage that describes a curse on the the literal "belly" and "thigh" of the woman, and unjustifiably translates that as "miscarriage" even though no pregnancy is mentioned and no other Bible translation I know of translates it that way.
christians can squirm and lie their way out of anything, including and up to the catholic church (one of god's kellyanne conways on earth) running a child molestation ring that would make hollywood blush
im curious if any christians in here would like to refute this passage
surely the baby of a cheating wife is 'still just an innocent baby that deserves a chance
", right?
Other than that single word that the NIV translates as "miscarriage", there's no indication anywhere in there that they were even describing pregnancy. No pregnancy or fetus is mentioned, and why would the test for adultery only apply to pregnant women? It's almost certainly a mistranslation by the version you used.
Body parts can be difficult translations in Hebrew, because ancient Hebrew often used euphemisms rather than refer to things scientifically, or use the same word to refer to two things close to each other. (Even in English there can be confusion - when someone says, "I got shot in the stomach", does it refer to their lower torso where the muscles are, or their actual digestive organ? If you say someone hurt their groin, did they strain their groin muscle or get kicked in the balls?)
But some translations are more likely than others. Whoever fed that passage to you used the NIV on purpose, because the NIV is the ONLY place I've ever seen that passage translated as "miscarriage". In every other translation it's a curse on the the women's belly or more specifically the womb (implying the woman wouldn't be able to have children again), not a curse on any baby. The words are actually literally "belly" and "thigh", but most scholars agree that "thigh" was used as a euphemism for the reproductive parts in Hebrew just like "groin" is used as a euphemism in English. But there's no word for "miscarriage" in there - that's something the NIV adds as a loose interpretation, probably without legitimate justification.
If you want to refer to the ancient Jewish Talmud, where the whole process is described in much more detail, they never once refer to pregnancy or miscarriage anywhere there either. So even 2,000 years ago that verse wasn't being interpreted in that way by the Jews who were actually using it. And the NIV translation wasn't done by anyone who had ever done that trial or ever would.
New Revised Standard Version (what I and many others consider the most competent, unbiased, direct translation out there):
When he has made her drink the water, then, if she has defiled herself and has been unfaithful to her husband, the water that brings the curse shall enter into her and cause bitter pain, and her womb shall discharge, her uterus drop, and the woman shall become an execration among her people.
King James Version (if you're into the OG stuff)
And when he hath made her to drink the water, then it shall come to pass, that, if she be defiled, and have done trespass against her husband, that the water that causeth the curse shall enter into her, and become bitter, and her belly shall swell, and her thigh shall rot: and the woman shall be a curse among her people.
American Standard Version
And when he hath made her drink the water, then it shall come to pass, if she be defiled, and have committed a trespass against her husband, that the water that causeth the curse shall enter into her and become bitter, and her body shall swell, and her thigh shall fall away: and the woman shall be a curse among her people.
English Standard Version
And when he has made her drink the water, then, if she has defiled herself and has broken faith with her husband, the water that brings the curse shall enter into her and cause bitter pain, and her womb shall swell, and her thigh shall fall away, and the woman shall become a curse among her people.
You can keep going - none of the other translations write that passage as "miscarriage". It's a new thing the NIV added.
The whole point of the passage is that if the woman has been cheating, and lies about it yet still agrees to be tested, that the priest will perform the test (giving normally harmless barley water) and God, with the approval of the couple, will judge. And the judgment will be in her inability to have babies again and social ostracization.
Of course, in practice it's completely irrelevant for Christians, as we don't even have Jewish priests nor are any of those rituals meant for us.