Welcome to the beginning of a series of articles on the stages of fetal development. In this particular one we will be discussing the first trimester. If you are searching for information on the second or third trimesters then stick around until I write them. LOL!
In the first twelve weeks however, amazing things are happening inside of you (or have happened), so read on to learn more…
Week 1 – Your Menstral Cycle begins
Believe it or not… you are not actually technically pregnant for the first two weeks! Yes you read that right… random but true. The pregnancy timeline actually begins on the first day of your last period, as your menstrual cycle and ovulation are counted as part of the process.
So on the first week this includes your last known period. During which time you can expect to experience some or all of the known side effects, bleeding, cramps, bloating, sore boobs, and PMS.
Week 2 – Your Fertile Window and Ovulation happen
Week 2 of the pregnancy timeline is typically your fertile window, with which you are undoubtedly familiar with if you planned to have a baby with your partner. It is the only time during the month when unprotected intercourse can lead to pregnancy. During ovulation your egg will be fertilised.
Your fertile window can vary as to when it actually is, but it is typically 6 days in length with ovulation happening on the sixth day. Signs of ovulation which can be tested naturally are, the consistency of your cervical mucus, an increase in basal body temperature and the feel and positioning of the cervix.
All women’s cycles are different of course, not every woman has a 28-day cycle, and not everyone ovulates on day 14 (although it is typically the norm). Some women can have a cycle as long as 40 days and will therefore ovulate a lot later, others will be fertile during their period.
Although you would never ovulate during your regular bleeding cycle, sperm can survive within your body for up to 5 days. Which is why your fertile window is 6 days in length even though you only ovulate for 24 hours. So if you have ever heard that you cannot get pregnant while on your period then this not exactly a lie… but it doesn’t mean that pregnancy is not a risk!
Week 3 – The Zygote descends the Fallopian Tube and becomes a Blastocyst
Once the egg has been fertilised it is known as a Zygote. Only a few hours after conception the zygote will begin to divide, until approximately 3 days after fertilisation, when it reaches a ball of 16 cells and is then called a Morula. The Morula will begin its long descent down the Fallopian tubes and this will take another couple of days. During this journey it will continue to divide and thus becomes a Blastocyst.
Week 4 – The Blastocyst Implants itself to the uterine wall and becomes an Embryo
The Blastocyst has finally finished its journey down the Fallopian tube and implants into the uterine wall. It does this by dividing into two distinct groups of cells. The inner cells will in time become your baby, and the outer cells transform into the placenta. The placenta is what surrounds your baby and connects it to the wall of the uterus. By undergoing this journey the Blastocyst has become an Embryo.
Week 5 – Rudimentary Heart and Nervous system
The Embryo is now the size of an orange seed. Although it doesn’t resemble a baby like shape just yet. It does look a bit like a tadpole and believe it or not it is even starting to grow a tail! But before you start to panic, don’t worry you aren’t giving birth to a frog! This tail is called the caudal appendage and it plays an important role in the development of the spine when it transforms into the coccyx or base of the spine.
What else is going on? A very basic heart exists within the embryo, but it is definitely beating. The start of a circulatory. system is beginning to form. There are two tubes that have formed. One of these is the neural tube which is the start of the nervous system and will grow into the spinal cord and brain, extending from the “head” to the “tail” of your Embryo. The second tube is the beginning of the digestive system and this extends from the “mouth” to the “tail”. This will eventually become the stomach, liver, pancreas, esophagus, and intestines.
Week 6 – Baby’s head, arms, and organs starting to take shape
The Embryo is now the size of a sweet pea and will take on a C-shaped curvature. You will also likely be relieved to know that it is starting to develop human features. No more frogs! There is the shape of a head along with very rudimentary eyes, jaw, chin and ear buds. There is also the beginning of very basic arms buds.
Inside there is also a lot going on too with some major organs that are taking shape, the kidneys, liver and lungs. The heart is continuing to beat and at this stage that has reached approximately 110 beats per minute.
Week 7 – Brain Cell Development and formation of the Kidneys
The embryo is the size of a blueberry and you will be glad to know that the tail has vanished. The most important thing that is happening this week is your baby’s brain development. The baby’s head is really taking shape and new brain cells are being produced at a rapid rate of 100 new cells per minute. The kidneys are coming along nicely too and are just about ready to start producing urine, which will happen soon.
Outside new features are continuing to form with the development of a mouth and tongue, as well as rudimentary lips and even tooth buds. The eyes now appear distinctly as two dark spots and there are two holes that will become nostrils. The arm buds are growing in length with little paddle hands at the ends becoming more distinct.
Week 8 – Growth Spurts and Nervous System Development
The Embryo is the size of a raspberry now with the largest part being the head. This is because the nervous system development is really starting to take off. The nerve cells are growing and making connections and these connections will become a vast neural network to enable the brain to communicate with the body.
There are huge growth spurts all over the body now causing other vast changes within the structure of the Embryo. In the face there is the start of a button nose and tiny eyelids to cover tiny eyes. The newest exciting development within the arms and legs is the appearance of cartilage and bones. This brings with it the beginnings of joint formation and soon to come will be elbows, knees and shoulders. Fingers and toes have also formed although these will be webbed, not separate.
Week 9 – The Development of the Placenta and Brand New Organs
The Embryo is the size of a green olive measuring a whopping 2.5 cm in length and growing at an amazing rate of a millimeter a day. If you haven’t felt tired already then you will likely start to really feel it in week 9 as this is the week when the placenta begins to develop. Your body is working overtime to grow the placenta, which will nourish your baby and supply it with oxygen via the umbilical cord.
The newest development in your babies body though is the construction of the liver, spleen and gallbladder, which will soon be fully formed. The bladder and urethra have separated from the digestive tract. The diaphragm is nearly fully formed and this will help your baby to breathe after being born. Another exciting development though is the start of small muscles causing reflex movements in the arms and legs.
Week 10 – From Embryo to Fetus – Functioning Organs and Systems
Good news this week, your Embryo will finally graduate to the status of Fetus and is now the size of a prune. The cartilage and bones are rapidly taking shape and the arms and legs can bend thanks to the development of joints and ankles. The face is continuing to take shape with growth to the nose, ears, and tooth buds.
Amazingly, even in this short time, there are now working systems of organs within the Fetus, the stomach and kidneys are clearing out digestive juices in the form of urine. The circulatory system is also functional with the heart containing all four chambers. The ventricles are sending blood to the Fetus’s lungs and body and the atria are taking that blood back. There will also be an increased blood supply within your own body to nourish the growing baby. You may notice blue veins appear on you breasts and abdomen as a result.
Week 11 – Detailed Development – Practicing Yawning, Swallowing and Chewing
Your baby is the size of strawberry and furthermore, the torso is getting longer to be in proportion with the head. The head also has more human features. The ears have completed their development and are now in their final shape. There is a tongue and palate in the mouth and open nasal passages. Your baby will now be practicing yawning, swallowing and chewing. The more detailed development has begun. There is the new growth of hair follicles all over the body and even the development of fingernail and toenail beds. The fingers and toes are no longer webbed but separate and the nipples are now visible.
Week 12 – Baby’s Brain Structure is Complete and Key Body Systems are Fully Formed
This is a pretty big week as the key body systems and vital organs are fully formed. Throughout his or her time in the womb your baby will perfect these systems, bringing them up to speed. The most exciting development this week though is that the babies brain structure is finally complete. The pituitary gland will begin to produce hormones and the thyroid gland is working on its own. Not to be outdone, the pancreas has already begun to synthesize its own insulin. In immune system development the babies bone marrow is already churning out white blood cells in preparation for the baby meeting germs in the outside world.
Furthermore, muscles in the digestive tract are developing, practicing their contractions so that the baby’s stomach can process food after birth. Your digestive system on the other hand is doing the opposite, it is slowing down to enable you to absorb nutrients from you food better. In more exciting news, your babies heart beat is now loud and clear on an ultrasound.
The Second Trimester
The second trimester begins at the start of week 13, but that is another article. So hang about while I write it and come back to read more. LOL.
If you have any comments about your pregnancy experiences during the first trimester then I would love to read about them so be sure to leave them below.
Alternatively if you have any questions at all about anything that I have missed then drop me a comment also and I will reply.
Jacqueline