Pregnancy is the continuous development of a new human being from the moment fertilization occurs. At fertilization, a distinct human organism comes into existence, already possessing its own genetic identity, including sex and many inherited traits. This is not a potential human, but a developing one, whose growth unfolds in an orderly, coordinated way over time.
Within about a week, implantation begins as the embryo embeds in the uterus and continues organizing itself. By just over three weeks after fertilization, a heartbeat can be detected. Soon after, the body plan becomes visible: arm and leg buds appear around four weeks, and by five to six weeks the developing child shows spontaneous and reflexive movements. At six weeks from fertilization, measurable brain activity is present and bones begin to form.
By seven and a half weeks, the hands can move together, fingers and toes become distinct, and behaviors such as hiccups may occur. At the beginning of the ninth week, the child has reached close to one billion cells and is now described as a fetus—a term that marks a stage of development, not a change in kind. At this point, the child can suck a thumb, swallow, grasp, touch their face, stretch, and sigh. By eleven weeks, there is active movement and exploration, with continued growth and maturation through the remaining months of pregnancy until birth.
Key Takeaways
From fertilization onward, pregnancy involves the growth of a distinct, living human organism, not the gradual creation of one.
Major life-signs such as heartbeat, brain activity, and purposeful movement appear very early in pregnancy.
Terms like “embryo” and “fetus” describe developmental stages, not differences in humanity or moral worth.
The continuity of development shows that abortion ends the life of the same human being who would otherwise continue growing toward birth.