Life in the Womb

At conception, also known as fertilization, a male sperm unites with a female ovum (egg). The single-celled human organism formed by the fusion of sperm and egg is known as a zygote.

Until 1965, physicians considered pregnancy to begin at fertilization, when the male sperm unites with the female ovum in one of the mother’s Fallopian tubes, creating a new human life. Since then, the American College of Obstetricians and Gynecologists has identified the beginning of pregnancy as implantation, when the tiny human being (now scientifically known as an “embryo”) implants in the mother’s uterus and begins to draw nourishment, eight to ten days after life begins.

The reasons for this change are disputed. Some argue the new definition was established to allow intrauterine devices (IUDs) to be characterized as contraceptives rather than abortifacients, since they can inhibit implantation.

But even if one concedes the new definition, the critical question is when a new human life begins, not when pregnancy begins. Once that new life has begun, any measure taken that destroys that life constitutes an abortion.

Many stages of prenatal development can be identified, especially in the early days and weeks of life when change takes place at an extremely rapid pace. The following are the primary stages:

• Zygote—A single-celled human being from fertilization until the first cell division
• Embryo—A human being from the time of the first cell division until approximately the eighth week of life
• Fetus—A human being from approximately the eighth week of life up until birth

To this list of stages of human development might be added: newborn, infant, toddler, child, adolescent, adult and senior—the continuum of human life which begins with conception.

Prenatal development and pregnancy can also be divided into trimesters:

• First Trimester—From conception to approximately 12 weeks gestation
• Second Trimester—From approximately 13 through 26 weeks gestation
• Third Trimester—From approximately 27 weeks gestation to birth

An embryo’s heart begins to beat between 18–24 days after conception.

An embryo’s brain waves can be detected six weeks after conception.

Based on the development of the nervous system, a fetus likely has the capacity to feel pain as early as 8-12 weeks gestation.

By nine weeks after conception, a fetus’s fingernails are forming.

The point in pregnancy after which a fetus is capable of living outside the womb is known as “viability.” As medical technology has improved, that point has been pushed back earlier and earlier in pregnancy. Babies born as early as 24 weeks routinely survive with medical assistance, and some have survived as early as 21 weeks.

Other important milestones of fetal development include:

• At 9 weeks after conception, a fetus is able to bend its fingers around an object in its hand, and sucks its thumb. All essential organs have begun to form. 
• At 11 weeks, a fetus is breathing amniotic fluid steadily and will do so until birth. 
• At 12 weeks, a fetus can kick, turn over, make a fist, open its mouth and press its lips together. 
• At 13 weeks, a fetus’s vocal cords and auditory sense are present. 
• At 20 weeks, a fetus can be startled by a loud external noise. 
• At 23 weeks, a fetus can demonstrate rapid eye movements (REM). 
• At six months, fine hair grows on the fetus’s head and eyebrows, and small eyelashes begin to appear. 
• At seven months, a fetus’s hands can support his entire weight.
• At eight months, a fetus weighs more than four pounds.
• During the ninth month from conception, a fetus gains half a pound per week. Of the 45 total generations of cell replication that will occur by mature adulthood, 41 have already taken place.