Buddhism doesn't view human life as gradually formed in embryo development; instead, many Buddhists believe that "the flux of consciousness from a previous being is necessary condition for the development in the womb of a body endowed with mental abilities which amount to sentience: feeling, identification, volition, sensory stimulation and attention" (Harvey 311)
Buddhism also emphasizes on four rare opportunities: "Human birth is hard to gain, hard for mortals is their life, to come to Dharma True is hard, rare the Buddha's arising" (Dhamapada Verse 182). Therefore, human life forms at contraception with consciousness, as the fetus grows, it would be more sensitive to pain and the external environment. .
Buddhists follow the five precepts, and the first of five precepts is no killing. Destroy any form of human life will yield bad karma, such as ill health, brevity of life, as well as birth in animal, hungry ghost or hell being realms. The karmic consequences of the act depends on the intention and the psychological state of the actors. Many would argue that all births are due to their previous karma, being aborted might well be the fetuses' past karma. Buddhism focuses on how to end samsara, the cycle of rebirth, in order to end all suffering. There was a story recorded in the commentary to the Dhammapada: there was a man had two wives, the first wife caused the second wife to have three miscarriages, and the second wife died from the third miscarriage. Before the second wife passed away, she made a wish to be reborn as an ogress to devour any children her rival might bear. She was reborn as a cat, and the first wife reborn as a hen. The cat ate the hen's eggs three times, and then ate the hen. The hen (the first wife) made a wish to eat the enemy and her offspring before she died. The hen reborn as a leopardess, and the cat reborn to a doe. As one could imagine, the cycle of revenge kept going until both sides met Buddha.