Life in the Womb
The life of a human being begins at fertilization (or conception), when a sperm cell fuses with an oocyte (egg) to produce a new human organism. This individual is called a zygote at the one-cell stage of development, an embryo through the first eight weeks, and a fetus from eight weeks until birth. Each of us was once a zygote, embryo, and fetus, just as we were once infants, toddlers, and adolescents. All of these terms refer to stages in the life of a member of the species Homo sapiens.
Day 1 (Conception)
A new member of the human species begins. The zygote has a complete and unique set of 46 chromosomes (23 from each parent), the entire genetic blueprint. He or she needs only a suitable environment and nutrition in order to develop himself or herself through the different stages of human life.
6 Days
The developing embryo, called a blastocyst at this stage, begins attaching to the wall of the mother’s uterus.
17-21 Days
17 days: Blood cells have developed.
19 days: The eyes start to develop.
20 days: The foundation of the nervous system has been laid.
18-21 days: The baby's heart begins to beat.
28-30 Days
28 days: 40 pairs of muscles have developed along the trunk of the new individual; the baby's arms and legs are forming.
30 days: Regular blood flow exists within the vascular system; the ears and nasal passages have begun to develop.
6 Weeks
The skeleton is complete and reflexes are present. The child has measurable brain waves.
7 Weeks
The baby has the appearance of a tiny infant, with fingers, toes, and ears.
8 Weeks
All organs are functioning—stomach, liver, kidney, brain—and all systems are intact.
9-10 Weeks
The baby squints, swallows, and retracts his or her tongue.
11-12 Weeks
The baby sucks his or her thumb and inhales/exhales amniotic fluid.
16 Weeks
The mother may begin to feel her child’s movements. The baby grasps with hands, swims, kicks, and turns somersaults.
18 Weeks
The vocal cords are working.
20 Weeks
A wealth of evidence indicates that, at least by 20 weeks, unborn children can experience pain. In the fifth and sixth months, the child responds to outside stimuli, including music and voices.
22 Weeks
Babies today are usually capable of surviving outside the womb (with assistance) at 22 weeks post-conception (24 weeks from the last menstrual period). They can often survive even earlier (including notable cases at 19 weeks from conception). This is called viability.
38 Weeks
The unborn child dramatically increases in size and weight during the second half of pregnancy until birth at about 38 weeks (40 weeks from the last menstrual period).
