Is a miscarriage the same thing as an abortion?

No. A miscarriage is a natural loss that God permits. It becomes an abortion only if the mother deliberately took something, such as an abortifacient pill, to cause the death of the child, and knew that is what she was doing. They are not the same thing. Keeping them apart matters, because grieving mothers are often tormented by the fear that they did something wrong. Start with what makes an abortion an abortion. It is the deliberate taking of an innocent human life in the womb. If any artificial method is used to abort the developing baby, at any stage, it is murder, and premeditated murder at that, because it is planned. That is why I say in my Bible study material on Genesis that the willful destruction of the unborn falls under the same divine prohibition as any other shedding of innocent blood: "Whoever sheds the blood of man, by man shall his blood be shed; for God made man in his own image" (Genesis 9:6). The human being in the womb is made in that image from the first moment. God infuses a soul into the embryonic cell at conception. He does not wait for the fourteenth day or the fortieth. Aristotle thought the soul arrived later, and Augustine and even Thomas Aquinas inherited that opinion from him, but they were working with the biology of their day. We are not. We know what happens in those first minutes, and we believe as Catholics that the soul is given at the moment of conception. Scripture treats the unborn as a person, never as tissue. "Before I formed you in the womb I knew you" (Jeremiah 1:5). Psalm 139 says God knit us together there. John the Baptist was filled with the Holy Ghost from his mother's womb and leaped at the presence of Christ (Luke 1:15, 41). Look also at Exodus 21:22. The Hebrew word there is yeladeha, "her children." It is not "fetus," it is not "embryo," it is a human child, and the word for coming out is the ordinary Hebrew word for being born, the same used in Genesis 25 and Genesis 38. Hebrew has perfectly good words for a miscarriage, and the inspired text did not use one. It used the word for a child. The Septuagint muddies this, and that is where a great deal of bad interpretation came from over the centuries, but the Septuagint is not the inspired text. Now the miscarriage. Sometimes a baby does not survive. The child dies in the womb for reasons no one chose and often no one can identify, and the mother's body senses that the child is no longer living and expels him. That is nature taking its course. There is no act of the will against the child's life, so there is no sin. In that case we say God made the decision to take the baby, and we leave it there. It is His to give and His to take. So the test is not what happened to the child; it is what the mother did and what she knew. If she swallowed a pill in order to end the pregnancy, and understood that is what the pill does, that is an abortion, and it is a grave matter that belongs in the confessional. If she did nothing of the sort, she has committed no sin whatsoever, and no priest, no relative, and no voice in her own head has the right to tell her otherwise. One caution does bear on this, because people do not always know it. Some artificial contraceptives work by making the womb inhospitable so a fertilized egg cannot implant. A woman who learns that about what she has been taking has something to bring to confession, not because she miscarried, but because of the method. As for the child, entrust him to the mercy of God. The Church has not defined the fate of infants who die without baptism. The Catechism says plainly that she can only entrust them to God's mercy (1261), and it notes that God is not bound by His sacraments even though we are (1257). That is speculation, and I will not pretend it is doctrine. But it is a real hope, grounded in the character of the God who said, "let the little children come to me."