Many people, including pregnant women, wonder when exactly a fetus becomes a baby. By "baby," they frequently mean a full-fledged, if very young and small, human being or human person. Embryology, the science of prenatal development, distinctly shapes the available answers to this question, as do ethical and political considerations.
The question of when a fetus becomes a baby is vital to many reproductive debates, including fertility technologies, cloning, embryonic stem cell research and abortion. Whether from those who identify themselves as prolife/anti-abortion or those who identify themselves as pro-choice/pro-abortion rights, most answers to this question are proposed in the context of the abortion debate.
As both pro-choice and pro-life historians note, the early 19th century discovery of conception--the fusion of egg and sperm cells--sparked a multigenerational, sometimes familiar-sounding debate over fetal status and abortion. Pioneering women doctors like Elizabeth Blackwell and Alice Bunker Stockham argued that life began at conception and was remarkably developed by quickening, or the pregnant woman's first sensations of fetal movement, the time then popularly understood as the beginning of life. Other physicians, like Edward A. Schumann, maintained that in some situations, "a small inconsequential fetus [could be] removed without concern."
Current Scientific Information
Visualization technologies like ultrasound and magnetic resonance imaging have greatly increased our knowledge of prenatal development. Yet science still defines conception as the beginning of life, at least in the biological sense.
The just-conceived prenatal life form is called a zygote. While migrating down the woman's Fallopian tube to her uterus, it is named a morula, and from days five to 12 post-conception, a blastocyst. The blastocyst implants in the nutrient-rich lining of the mother's uterus. From day 12 through week six, this being is termed an embryo.
According to the American Pregnancy Association, "everything that is present in an adult human is now present in the small embryo." From week seven until birth, it is named a fetus; however, scientific facts and terminology regarding prenatal development cannot on their own answer the question of the prenatal being's ethical and political status.
Pro-choicers frequently do not dispute that the prenatal life form is biologically alive. At the same time, as Dalton Conley observes, they view the fetus as "an individual under construction" and thus not yet a person. They do disagree about when in that construction process it becomes a baby. That transition might occur, for example, at certain milestones in brain development; at viability, the earliest age the fetus can survive outside the mother's womb, which is currently around 20 to 24 weeks; or at the moment of birth. Diana Philip from the National Coalition of Abortion Providers comments: "Pro-choice docs would say that it is not their business to determine for a patient when life begins. Ultimately each patient determines the value and definition of life...within her own mind and heart."
Donna J. Harrison, MD, president of the American Association of Pro Life Obstetricians and Gynecologists, argues that if the prenatal being "is nourished and protected, it will proceed uninterrupted through the developmental stages of embryo, fetus, newborn, toddler, child, teen, adult and aged adult: one continuous existence... The real argument in the abortion debate is whether or not this human being is a 'person,' with all the...protections of 'personhood.'" She compares the exclusion of prenatal beings from personhood to the exclusion of African-Americans. Other pro-lifers connect the exclusion of prenatal life forms from personhood to the exclusion of other groups, such as women, Latino/as, Native Americans, people with disabilities, LGBT (lesbian-gay-bisexual-transgendered) persons, the poor, and death row prisoners.