Fetal Development

  • Week 1: Last Period

    Week 1: Last Period
    We start this process at the mother's last period. This is the most accurate way of figuring out when the baby will be born (It should take about 40 weeks give or take). Week 1 also marks the beginning of the first trimester which will last until week 14.
  • Period: to

    First Trimester

  • Week 2: Fertilization

    Week 2: Fertilization
    In the falopian tube an egg is waiting for a sperm cell to fertilize it. The egg is only 1/200th of an inch which cannot be seen with the naked eye. When fertilization happens, only one sperm is meant to break through and once this has happened the egg instantly shuts down and no other sperm will be allowed to attach.
  • Week 3: Division of Cells

    Week 3: Division of Cells
    Once fertilized, the egg is going to begin floating out of the fallopian tubes. It takes about 3 days to finally implant into the uterus. And while this is happening there is rapid division going on inside the egg. It will split into 2, then 4, then 8, etc.
  • Week 4: Im-PLANT-ation

    Week 4: Im-PLANT-ation
    The egg, now called a blastocyst, will continue multiplying and create a placenta for the embryo. The embryo is still very small but once in the uterus it will begin developing extremely fast. Implantation can take up to three days and once it attaches, hCG will be released to stop the uterine lining from shedding.
  • Week 5: Embryo Time

    Week 5: Embryo Time
    The embryo is no longer super tiny; since implantation it has grown to the size of a pinhead and kind of looks like a sea horse. The embryo will begin developing nerves and start to get oxygen and other nutrients from its mother. Week five is also when Mum figures out she's pregnant because she wouldn't have had her period.
  • Week 6: WE GOT A PULSE

    Week 6: WE GOT A PULSE
    The one chamber of the embryo's newly developed heart begins beating at this point. The embryo is also preparing for other new developments such as eyes, arms, legs, and the use of an umbilical cord. All other major body organs have already been made, they just aren't fully developed.
  • Week 7: Appendages Begin to Grow

    The cells that were put to the side to become arms and legs begin developing. They start out as buds and the hands won't have any fingers. Those will develop in about two weeks.
  • Week 8: Tiny Movement

    The fetus has been sort of moving for a little bit but now it actually has limbs and major muscles working. It practices moving but Mum won't be able to feel it until way later in the pregnancy. The fetus' face is also forming and it's heartbeat is going twice as fast as an adult.
  • Week 9: Findin' the Phalanges

    The little paddles on the ends of the arms and legs begin developing fingers and toes that are webbed. The embryo has grown to about an inch and is developing its tongue, larynx, eyelids, and anus. Movement now mostly involves swimming in fluid.

    From week 10 on, the embryo is now called a fetus. It has grown to the size of a strawberry, can move around, and many facial features and limbs can be seen. The fetus' unique fingerprints can now be seen. The sex of the fetus will be determined in a few weeks.
  • Week 11: Neurons Multiply

    The toes and fingers have separated and the baby's brain will produce more than 250,000 nerve cells. It is too early however to determine sex.
  • Week 12: You've Got Nails

    Week 12: You've Got Nails
    With the fingers and toes separated, nails will start to form but won't be completely hardened until later in the pregnancy. Week 12 is also when the baby's face becomes more recognizable as a face.
  • Week 13: Fetus begins Flexing and Kicking

    Week 13: Fetus begins Flexing and Kicking
    Muscles are moving in jerking and kicking ways. Movements go unnoticed by Mum and will continue for a while. The baby will move until there is no more room in the uterus.
  • Period: to

    Second Trimester

  • Week 14: HORMONES

    The start of week 14 means the beginning of the second trimester. Hormones will be released into the baby's body and this will cause a number of different things. Hair will be seen and the ears will be developed.
  • Week 15: Bones and Muscles Grow

    Your baby's legs have grown longer than the arms and the body is longer than the head. This is due to muscle and bone growth. The baby will probably start kicking.
  • Week 16: Baby Making Faces

    The baby has learned how to breathe and most of the face has developed so most of the faces the baby makes is frowns and squinting.
  • Week 17: Fatty Fetus

    Fat stores under the baby skin and this will provide energy to keep your baby warm after birth. Eyes remain closed and the skeleton is transforming cartilage to bone.
  • Week 18: Baby is All Ears

    The baby will start to hear things going on inside the mothers body. And will become startled by loud noises.
  • Week 19: He or She?

    The genitals are now recognizable. So the sex of the baby can now be determined in an ultrasound.
  • Week 20: Hey! Mum is Halfway Done!!

    The baby is around eleven ounces and is about seven inches long. It can react to sounds and recognizes it's mothers voice. There should only be about 20 weeks left in the pregnancy.
  • Week 21: Baby's Nourishment Upgrades

    Bone marrow is making blood cells and its body has upgraded to being able to absorb small amounts of sugar from swallowed amniotic fluid.
  • Week 22: Baby Can Now Taste

    With the tongue done, taste buds will form. The baby is hypersensitive to whatever it's mother is doing and will react to just about anything.
  • Week 23: Let's Get Physical

    Week 23: Let's Get Physical
    The baby is now moving around and learning how to balance. The inner ear is developed and that's why it's able to turn about. Skin pigment and the pancreas begin forming around this time too.
  • Week 24: IT'S BREATHING.... sort of

    The baby is only practicing breathing but it's body is becoming accustomed to unconsciously using its lungs.
  • Week 25: WHAT'S THIS

    So the baby's hands do a lot of exploring in the womb while it still has room. It will hold onto itself and to its umbilical cord. Also by week 25 the sex organs are done developing.
  • Week 26: Second Trimester Ends

    By the end of the second trimester, the baby will be about 14 inches long and will weigh a little over a pound. Painless contractions start now and you can actually play with the baby.
  • Period: to

    Third Trimester

  • Week 27: IT'S DARK IN HERE

    Week 27: IT'S DARK IN HERE
    The baby can now see but it's not going to be much because it hasn't developed the sensory it needs to respond to light. The baby is able to blink, sleep and stay awake.
  • Week 28: "Mother? Is that you?"

    Ears are working and the majority of what it'll hear is its mother so it makes sense that the baby now can recognize and respond to its mothers voice. The baby will also fall asleep and wake up in intervals.
  • Week 29: Baby is a forceful tenant

    The baby has most of its muscles done and so it it's going to start moving around. The movement will be very often until the womb becomes too cramped. This is great for the baby but it's poor Mum has to deal with it constantly doing flips.
  • Week 30: Gainin' Weight

    The baby looks really thin and wrinkly and needs to put on pounds and fast. Mum will gain weight and some of it is going to the baby in order for it to grow more. With this weight gain means less room in the uterus and so it will not kick around as much.
  • Week 31: And then there was Light...

    The eyes can start to respond to light and the baby reacts to many of the things such as noise going on in the outside world. Most organs are beginning to mature in preparation for birth.
  • Week 32: Reproductive Development Continues

    The baby tries to move but now the uterus is cramped. The baby will also sleep most of the day. At this week a baby boy's testicles will move to the scotum. A baby girl's clitoris will become prominent.
  • Week 33: Fuzziness Begone

    The lanugo that the baby has is starting to disappear so that real hair can grow in its place. Mum is also going to gain more weight so that most of it can go to the baby.
    How selfish.
  • Week 34: Still Growing

    Fat is going to build up in the arms and legs as well as the rest of the body to make it so the rapid growth is being leveled out.
  • Week 35: Cat-Like Reflexes

    Week 35: Cat-Like Reflexes
    Well maybe not cat-like per se but you understand. It's reflexes are going to be coordinated so they work properly. The baby is still trying to work up the fat it needs so it's not ready to be born yet.

    This should be the last month of the pregnancy. The baby is getting chubbier and contractions will most likely be felt in the womb. The baby drops to birth position which makes it easier for Mum to breathe, but trouble walking and frequent bathroom trips are what takes its place.
  • Week 37: Mum is "at term"

    At this point the baby is close enough to being fully developed and so it's Mum's water could break at any second.
  • Week 38: Done Diddly Developing

    38 weeks after the end of Mum's last menstrual cycle, that weird looking embryo has grown into a fat baby who has just finished developing and is prepping for birth. It has grown hair and is no longer wrinkly.
  • Week 39: Any Day Now...

    The baby is about to come out. It's going to continue to beat up your lower abdomen as it reach it's final birth position. Contractions may start but that doesn't necessarily mean you're going into labor.
  • Week 40: IT'S TIME

    Week 40: IT'S TIME
    Mum's body is tired of the seven pound, 20 inch long baby in her uterus so contractions are going to start. Sometimes the baby will want to come out sooner and sometimes later but around the 40 week mark it's just a matter of time. Also congrats to the new Mum!