Wasn't there once a pledge doctors used to have to make about not performing abortions?

Yes indeed! Please listen to the words of Hippocrates, the great ancient Greek physician (died 377 BC). The following is the Hippocratic Oath--once required of doctors to recite in this form. (I have edited it for clarity and relevance to your question.)

I swear by Apollo the physician...that, according to my ability and judgment, I will keep this Oath and this covenant. To reckon him who taught me this Art equally dear to me as my parents, to share my substance with him, and relieve his necessities if required; to look upon his offspring on the same footing as my own brothers, and to teach them this Art, if they shall wish to learn it, without fee or stipulation; and that by precept, lecture, and every other mode of instruction, I will impart a knowledge of the Art to my own sons, and those of my teachers, and to disciples who have signed the covenant and have taken an oath according to the law of medicine, but no one else. I will follow that system of regimen which, according to my ability and judgment, I consider for the benefit of my patients, and abstain from whatever is deleterious and mischievous. I will give no deadly medicine to anyone if asked, nor suggest any such counsel; and in like manner I will not give to a woman an abortive remedy. Whatever, in connection with my professional practice, or not in connection with it, I see or hear, in the life of men, which ought not to be spoken of abroad, I will not divulge, as reckoning that all such should be kept secret. While I continue to keep this Oath unviolated, may it be granted to me to enjoy life and practice of the Art, respected by all men, in all times. But should I trespass and violate this Oath, may the reverse be my lot.

What do you notice about the Oath? A number of things strike me. Not to counsel naivety, still I urge us as a society to consider how far we have wandered since the days of the fourth century BC physician.
* No tuition fees for medical school!
* No euthanasia. (Sorry, Doctor K.)
* No abortion.
* No breach of confidentiality.
* A curse is invoked on any physician who reneges on his pledge.
* Addendum:

(Used with permission from John Clayton and Does God Exist? May/June 2010)

HIPPOCRATIC OATH CHANGES. A recent survey of medical schools in the United States shows that there have been major revisions in the Hippocratic Oath that doctors take as a reflection of how they will use their expertise. One hundred and fifty medical schools were surveyed with 98 percent of their graduates taking the oath their schools presented to them. Only one of those schools used the classical version of the oath. Other schools deleted sections that included the avoidance of sexual contact with patients, references to a covenantal relationship with God, and a refusal to do abortions and euthanasia. It is pretty obvious that the medical profession has given in to cultural pressure to allow doctors to do things that would have been unthinkable not too many years ago. Source: Journal of the American Scientific Affiliation, March 2010, page 3.

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