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.

The sperm and the egg unite to create a unique single-celled human, the zygote. From day one the unborn baby has all the genetic instructions to form the child’s distinct hair color, height and gender. There is enough genetic variation that no two humans will ever be genetically identical! In the week after conception this tiny life follows a predictable set of cell divisions while travelling 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. This week, the unborn baby attaches to his mother in a process called implantation.

At first, the zygote and early embryonic cells can become almost any type of cells in the human body. Now the cells specialize more and more based on their position. Brain tissue and heart tissue begin to develop. This week, a home pregnancy test can accurately confirm the whether a new human life is growing within the mother.

In week 5, the heart starts beating rhythmically, moving oxygen throughout the developing baby. Without the beating heart, the unborn baby cannot survive. The neural tube, which becomes the brain and spinal cord, also forms.

In week 6, the heartbeat can usually be detected in an ultrasound. The heart keeps beating rhythmically, moving oxygen-rich blood throughout the developing embryo. The eyes, lungs and limbs start taking shape.

In week 7, the unborn baby is 10,000 times bigger than he was at conception, about the size of a blueberry. The unborn baby starts moving and responds to light touch. 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 week 8, brain waves have been recorded from a baby the size of a jellybean, showing that neurons are already beginning to connect. The baby can quickly move his arms and legs, as if startled, showing that the nerves and muscles are already working together. The face is taking shape with eyes, nose, mouth, and a tiny tongue.

In week 9, the unborn baby spontaneously moves his arms, and legs one at a time. The baby even hiccups! The baby’s heartbeat peaks this week around 170 beats per minute, nearly twice as fast as mom’s. Tiny toes start forming. Boys and girls start growing differently.

By week 10, more than 90% of the body parts have formed. Already, the unborn baby will show a preference for either his right or left hand as he moves in the womb. The unborn baby’s heart now has all four chambers.

In week 11, the baby is called a fetus. The baby moves a lot, and does not usually stay still for more than 5 minutes at a time! The baby can yawn, stretch, and touch his face. The first hair follicles start growing. Male and female genitalia start developing.

By week 12, 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, he will curl his toes. The earliest in utero surgeries have been performed at this age, although most are performed later in pregnancy.

In week 13, the unborn baby’s heart pumps about 6 quarts of blood per day, enough to fill a large slow-cooker. The tissue under the nose has fused, giving the baby a unique facial identity. The fetus practices breathing and starts peeing in the amniotic fluid.

In week 14, the fetus moves his hands more slowly as he approaches his face, showing that he is planning his movements. This week an ultrasound can reveal whether the baby is a boy or a girl. The intestines start absorbing nutrients and several eyelashes have formed.

Scientific advancements provide clear evidence that the unborn baby feels pain by 15 weeks gestation, and possibly even earlier. The unborn baby may start to smile and can move each finger separately. Boys and girls move differently in the womb.

In weeks 17 and 18, the mother may feel her unborn child moving. Also, a fetus as young as 18 weeks responds to a painful procedure with a stress response. Antibodies from the mother may transfer to the fetus now. Mature tastebuds cover the unborn baby’s tongue.

In weeks 19 and 20, the unborn baby may start responding to loud noises like a car horn. The unborn child clearly responds to a painful procedure with grimacing, recoiling, and a spike in stress hormones. His vocal cords sometimes vibrate as if he is crying. The heart has beat over 20 million times, pumping enough blood each day to fill a small car’s gas tank.

The youngest premature baby to survive was born at 21 weeks gestation (133 days premature). 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 month six, the fetus responds to loud noises with a startle response. While every baby is different, most of the unborn open their eyes this month. The baby is beginning to sense light, and is already drawn to faces. More than half of premature babies born at the beginning of this month survive, and by the end of the month more than 90% of premature babies survive.

By month 7, more than 92% of premature babies survive. The unborn baby now cycles through a variety of sleep and wake patterns, starts to smell the amniotic fluid, shows signs of simple learning. Scientists can even measure brain responses to light and sound in the womb. This month, the brain contains more neurons than it will at any other time in life.

In month eight the baby’s brain is ready to learn! At 34 weeks, neurons are creating 40,000 new connections every second. With repeated exposures, the unborn baby can learn flavors, nursery rhymes, songs, and even words that he will recognize after birth! He can recognize his mother’s voice and makes happier faces when she eats sweeter foods.

In the last month, the baby prepares for birth by gaining about half a pound each week. After 37 weeks, he is considered full-term and he is ready to breathe on his own. After birth, the baby prefers flavors he encountered in the womb. He  will also imitate the melody of his mother’s native language when he cries, so babies from different cultures sound different.

Around 40 weeks, the baby is born! At birth, the baby is ready to clear amniotic fluid from his lungs and take his first breath. Though his vision is limited, he can already recognize his mother by scent, voice, and even sight. Far from passive beings focused on survival, newborns show an incredible ability to sense, learn, and respond to the world around them.