The first week of pregnancy starts from the first day after someone's last menstrual period. Pregnancy usually lasts from 38-42 weeks.
After the egg has been fertilized a sperm, it starts a rapid cell division and travels up to the uterus. The combination of the egg and the sperm's chromosomes determines the baby's sex and physical characteristics.
After fertilization of an egg, all of the DNA needed to make it human are present. The cells continue rapid cell division as it travels from the fallopian tubes through the uterus and embeds itself into the uterus' lining.
The fertilized egg, also known as a blastocyst, implants itself to the uterine wall where it releases hCG, a hormone used for detecting pregnancy. The rapid increase of hCG levels produces the symptoms for pregnancy.
The blastocyst multiplies quickly and divides into the placenta and the baby. By the end of the week, the baby's spinal cord and brain starts to form.
The mother can become extremely tired because of the rapid development of the baby. The baby's heart starts beating, its brain divides into five parts and their optic pits form.
The baby's lungs, liver, mouth, ear, vocal cords, limbs, and other major organs are developing.
The baby's limbs continue to grow and it starts to move. Its facial features are visible and the mother goes to her first prenatal visit.
The head appears larger than the rest of its body because of the rapid delevopment of the brain. The fingers and toes become more noticable and cartilage begin to form.
It's now called the fetus and they're about the size of an inch. Their fingerprints are now visible, and their hair follicles begin to form.
The fetus' reproductive organs and tooth buds begin to form and cartilage starts to become bones. Its neurons multiply, totaling to about 250,000 a minute.
Its pancreas produces insulin and nails starts to form. They start to move a lot.
The fetus can flex their limbs, open and close its mouth, and suck its thumb.
The baby starts to pee in the amniotic fluid, and they become covered with very fine hair to protect them from the fluid they currently live in.
The head and the body is more proportional, bones and muscle continue to grow, and they can now taste. Some mothers may feel the movement of the fetus.
Facial expressions are noticable. They can hear voices, sleep, breathe and kick around.
The baby is about 5 ounces and 9 inches in length. They develop fat under their skin to help keep them warm, and they start to poop.
Vernix forms on the baby's skin to protect them from the water. They hear sounds, sleep and even dream.
The baby's genitals can be recognized, and their hair continues to grow.
It can now recognize different voices. Their heartbeat can be heard and, the mother can feel its movements.
The baby starts producing its own blood cells and absorbing sugar.
The fetus has a regular sleep-wake cycle, and their taste buds start to form.
They may know their different positions. Their pancreas continues to grow and now produces their own insulin.
They start to breath more as they inhale and exhale the amniotic fluids. They have a 36% chance of survival if they are born now.
They explore their living quarters using their fully developed hands. The parts of the spine form, brain cells start to mature, and their sex organs become fully developed.
The eyes start to open. They become really active and are sensitive to touch.
It can open its eyes and blink. Its hairs continue to grow and muscle continues to develop.
They can recognize the mother's voice and respond to it when heard. They can dream.
They can taste, feel pain and follow the light. Their movements lessen because of the increasing amount of space they take up.
They baby gains weight, produce its own red blood cells, have smoother skin, and control its own temperature.
Its major organs starts maturing. Their eyes can fully open and respond to the light and darkness.
The baby has a lot less movement, and their reproductive organs continue to develop.
The baby drinks and pee constantly. The mother will gain pounds that will go towards her and her baby.
The baby is about 18 inches in length and weighs five and a quarter pounds. They gain a lot of fat in their limbs.
They continue to gather fat under their skin and have reflexes.
They continue to get fatter and may position themselves into the birth canal.
The mother is considered ready to give birth and may often experience vaginal discharge.
The baby continues to gain weight and eat up most of the fluids in their current home.
There is very little movement in the belly, and the lanugo that covers the baby is gone.
The baby is ready to come out into the world at any second. It's normal for the mother to become very sensitive around this time.