A new human being forms at fertilization, when a man’s sperm fuses with a woman’s egg. Within the next two decades, that newborn becomes a 30 trillion cell adult! Before a new life can form, a woman’s body must prepare for pregnancy, and a man’s body must produce sperm.

In the first week, the sperm and the egg unite to create a unique single-celled human, the zygote, with all the genetic instructions to form an adult with distinct physical features. The embryo follows a predictable set of cell divisions for the first week of pregnancy, forming a morula and blastocyst as the developing human travels through the mother’s fallopian tubes.

Just as infants need a safe, nourishing environment to grow outside the womb, the embryo needs a safe place to grow for the next 37 weeks. During the second week, the unborn baby attaches to his mother in a process called implantation.

Remember how the zygote and the early embryonic cells could become many different types of cells in the human body? In the third week, the cells specialize based on their position in the embryo. Brain tissue and heart tissue begin to develop.

In the fourth week, the embryonic heart starts beating. The neural tube, which becomes the brain and spinal cord, forms. At this point, a woman has likely only been aware of her pregnancy for one week.

In the fifth week after fertilization, the unborn baby is 10,000 times bigger than he was at conception, about the size of a blueberry. Almost all the major organs have started to form, and the brain starts growing at an average rate of 250,000 neurons per minute.

In the sixth week after conception, the embryo starts moving and responds to a light touch. This shows that neurons and muscles form functional connections, the same connections that will underly complex thought processes in an adult. The lips and the nose continue forming this week.

In the seventh week after conception, networks of neurons produce brain waves that have been recorded as early as 6 ½ weeks after conception. The embryo spontaneously moves his arms, hands, and legs, and may even hiccup. The embryo’s heart now has all four chambers.

During the first eight weeks of development, more than 90% of the body parts have formed. Already, the embryo will show a preference for either her right or left hand as she moves in the womb. The eyeballs finish forming.

The fetus moves a lot! In fact, in the ninth week after conception, the fetus does not usually stay still for more than 13 minutes at a time! Male and female genitalia start developing.

By the tenth week after conception, the fetus’s heart has beat over 10 million times! The fingernails start growing and fingerprints start forming. If something tickles the sole of the fetus’s foot, she will curl her toes. Tooth buds are developing as well.

In the eleventh week after conception, the fetal heart pumps about 6 quarts of blood per day. Furthermore, antibodies from the mother transfer to the fetus, so vaccines given to the mother often provide the child with initial protection against some diseases as well.

In the twelfth week after conception, the intestines start absorbing nutrients and the fetus starts making goal-oriented hand movements. Mature tastebuds cover the tongue, and the placenta provides a barrier that protects against most bacteria and some viruses.

At 13 weeks after conception, the evidence points to the fetus being able to experience pain. Eyebrows finish forming and the fetus moves each finger separately. Boys and girls move differently in the womb, and may respond to loud noises.

In the fifteenth and sixteenth week after conception, the mother may feel her unborn child moving. Also, one research study shows that a fetus as young as 16 weeks after conception responds to a needle entering his hepatic vein with a stress response that includes recoiling and increasing circulating stress hormones in his bloodstream.

By the seventeenth and eighteenth week after gestation, the fetus shows a clear response to pain in multiple studies, and at least one brain pathway is mature enough to create a perception of pain. The fetus also practices breathing, crying, and breastfeeding in the womb. The fetal heart has beat over 20 million times and circulates about 55 quarts of blood per day.

The youngest premature babies to survive have been born in the 19^th week after conception (21 weeks gestation). As hospitals invest in life-saving technologies to save their smallest, most miraculous patients, the age of viability gets younger and younger, bringing joy and hope to many families.

In the sixth month, the fetus consistently responds to loud noises, music, reading, and singing with changes in behavior. The eyes continue maturing and respond to changes in light. The fetus practices breathing in the womb.

In the seventh month of pregnancy, the fetus shows a variety of sleep and wake patterns throughout the day. The fetus overproduces neurons such that at 28 weeks gestation, he has more neurons than he will ever have again. The fetus can start learning sound patterns, and can smell different odors in the amniotic fluid.

In the eighth month of pregnancy the fetal brain is ready to learn! At 34 weeks gestation, neurons are creating 40,000 new connections, called synapses, every second! With repeated exposures, the fetus can learn flavors, nursery rhymes, songs, and even words that she will recognize after birth!

In the ninth month, the lungs finish maturing and the baby is born. In the womb, the infant’s lungs are half-filled with amniotic fluid, but the pressure of a vaginal birth helps push some fluid out, or into the lymph system. Most babies are born around 40 weeks gestation. A newborn has terrible visual acuity and limited color vision. However, she can identify her mother simply by her smell, voice, or a silent video of her face.