Destroying the undeveloped embryo of the soul in the womb is sinful.
As stated in the Amara-kosa dictionary, bhruno’rbhake bala-garbhe: the word bhruna refers either to the cow or to the living entity in embryo. According to Vedic culture, destroying the undeveloped embryo of the soul in the womb is as sinful as killing a cow or a brahmana. In the embryo, the living entity is present in an undeveloped stage. The modern scientific theory that life is a combination of chemicals is nonsense; scientists cannot manufacture living beings, even like those born from eggs. The idea that scientists can develop a chemical situation resembling that of an egg and bring life from it is nonsensical. Their theory that a chemical combination can have life may be accepted, but these rascals cannot create such a combination. This verse refers to bhrunasya vadham–the killing of a bhruna or destruction of the embryo. Here is a challenge from the Vedic literature. The crude, atheistic understanding that the living entity is a combination of matter belongs to the grossest ignorance.
Source: A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “Srimad Bhagavatam”, Ninth Canto, Chapter 9 – Text 31
