There is a passage that describes a procedure that a husband is to perform if he suspects his wife of committing adultery. He is to go to the priest, and they prepare a drink. The woman then drinks it, and it will or won't affect her depending on if she is guilty.
This passage is used by abortion advocates to claim that Christians cannot judge them, alleging that God himself caused abortions.
This, just like a passage about fornication that is also commonly assaulted, is a translation issue. The NIV renders the passage as follows:
Numbers 5:21-22, 27 (NIV)
21 here the priest is to put the woman under this curse—“may the Lord cause you to become a curse among your people when he makes your womb miscarry and your abdomen swell.
22 May this water that brings a curse enter your body so that your abdomen swells or your womb miscarries.”
27 If she has made herself impure and been unfaithful to her husband, this will be the result: When she is made to drink the water that brings a curse and causes bitter suffering, it will enter her, her abdomen will swell and her womb will miscarry, and she will become a curse.
Therefore, according to the NIV, this is an abortion inducer. Now, let's see how the text is rendered in the KJV (and most other Bibles as well):
Numbers 5:21-22, 27 (KJV)
21 Then the priest shall charge the woman with an oath of cursing, and the priest shall say unto the woman, The Lord make thee a curse and an oath among thy people, when the Lord doth make thy thigh to rot, and thy belly to swell;
22 And this water that causeth the curse shall go into thy bowels, to make thy belly to swell, and thy thigh to rot: And the woman shall say, Amen, amen.
27 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.
Obviously, when reading the NIV, "thigh" has been changed to "womb", and "rot/shrink" has been rendered as "miscarry". This is an interpretation, not a translation, and on top of that, it's completely inaccurate, and leaves an entirely wrong impression of what's going on. The woman would not miscarry if guilty, she would get sick in a distinct way that would declare her guilt.
The concoction that she was to drink was made of two ingredients - blessed water and dust from the floor of the tabernacle. Obviously, this would have no effect whatsoever outside of supernatural intervention from God on behalf of the man if the woman was guilty.
If the woman was innocent, the husband loses the offering, and she's completely blameless. If she's guilty, she's put to death - but so would a guilty male adulterer:
Leviticus 20:10
10 And the man that committeth adultery with another man's wife, even he that committeth adultery with his neighbour's wife, the adulterer and the adulteress shall surely be put to death.
Note also that pregnancy is not even mentioned in Numbers chapter 5. So no, this is not describing an abortion potion or attributing a magical affect to the concoction of water and dust itself. God supernaturally intervened publicly back in the Old Testament when dealing with the Jews because He dealt closely with them as a special nation.
In conclusion, pregnancy is never mentioned in the passage, and the judgement was for a sign indicating guilt that was supernaturally carried out by God as a public witness to the Israelites of His presence.