I suppose this is common sense but here is Calvin on abortion related principle from Exodus 21:22
22. If men strive, and hurt a woman. This passage at first sight is ambiguous, for if the word death 39 only applies to the pregnant woman, it would not have been a capital crime to put an end to the foetus, which would be a great absurdity; for the foetus, though enclosed in the womb of its mother, is already a human being, (homo,) and it is almost a monstrous crime to rob it of the life which it has not yet begun to enjoy. If it seems more horrible to kill a man in his own house than in a field, because a man’s house is his place of most secure refuge, it ought surely to be deemed more atrocious to destroy a foetus in the womb before it has come to light. On these grounds I am led to conclude, without hesitation, that the words, “if death should follow,” must be applied to the foetus as well as to the mother. Besides, it would be by no means reasonable that a father should sell for a set sum the life of his son or daughter. Wherefore this, in my opinion, is the meaning of the law, that it would be a crime punishable with death, not only when the mother died from the effects of the abortion, but also if the infant should be killed; whether it should die from the wound abortively, or soon after its birth. But, since it could not fail but that premature confinement would weaken both the mother and her offspring, the husband is allowed to demand before the judges a money-payment, at their discretion, in compensation for his loss; for although God’s command is only that the money should be paid before the judges, 40 still He thus appoints them to settle the amount as arbitrators, if the husband should chance to be too exorbitant. We plainly perceive, by the repetition of the lex talionis, that a just proportion is to be observed, and that the amount of punishment is to be equally regulated, whether as to a tooth, or an eye, or life itself, so that the compensation should correspond with the injury done; and therefore (what is first said of the life 41 ) is correctly applied also to the several parts, so that he who has plucked out his brother’s eye, or cut off his hand, or broken his leg, should lose his own eye, or hand, or leg. In fine, for the purpose of preventing all violence, a compensation is to be paid in proportion to the injury. But although God commands punishment to be inflicted on the guilty, still, if a man be injured, he ought not to seek for vengeance; for God does not contradict Himself, who so often exhorts His children not only to endure injuries patiently, but even to overcome evil with good. The murderer is to be punished, or he who has maimed a member of his brother; but it is not therefore lawful, if you have unjustly suffered violence, to indulge in wrath or hatred, so as to render evil for evil. Since this error was rife among the Jews, our Lord refutes it, and teaches that the punishment, which is publicly awarded to the wrong-doer, is not subservient to every man’s private passion, so that he who is offended should make haste to retaliate. (Matthew 5:38.) Nor indeed are these words addressed to them in order to inflame or excite the desire of vengeance, but all violence is restrained by the fear of punishment.
John Calvin, Commentaries on the Last Four Books of Moses, trans. Charles William Bingham, Grand Rapids, Michigan: Eerdmans, 1950, 3:41,42.