Fetal development is the process through which your baby will grow from a couple of cells to a small human. It’s exciting to observe and if you know what stages to expect your pregnancy will be a lot more manageable, especially if its your first.

If you are pregnant, congratulations! The next few months are going to be filled with wonder and questions as to what is going on inside you. You will soon start to wonder things like: When will its heart start beating?. When does the kicking start? Can it hear me? And of course is it a boy or girl so I can stop calling it, “it”?


Luckily the course of fetal development is predictable. Your pregnancy calendar can be segmented into weeks during which you will notice slight changes from one stage to the next. Expect at 40 week period for the full pregnancy (this starts counting on the first day of your latest menstruation). Premature babies usually arrive before the 37th week of pregnancy.

The series of articles on fetal development will be segmented into the three trimesters of pregnancy and we will see what happens week by week during each trimester.


Weeks 1, 2 and 3: Getting ready & Fertilization

In the first two weeks of the first trimester the female body is getting ready for ovulation and potentially implantation. Yes this is the beginning of of your usual period, and you might say, “how is that important or even part of my pregnancy?”. Well theoretically every new menstruation period is the beginning of a potential pregnancy. So when your uterus is ready to potentially host a fertilized egg, ovulation will begin. Typically, ovulation occurs between 11 and 21 days from the first day of the menstrual period.

Once the egg has left your ovary and reached the bottom of the Fallopian tube it is ready for conception. We wont be including the talk about the birds and the bees in this article, For conception to occur, the sperm will have to travel through the cervix into the Fallopian tube and penetrate the egg to create a zygote. This zygote is typically a set of 46 chromosomes, 23 belonging to the mother and the other 23 to the father. These chromosomes determine the baby’s traits, gender, and possibly intelligence and personality. If more eggs are released and fertilized, one might have multiple zygotes, otherwise known as triplets, twins etc.

Next, the fertilized egg travels through the Fallopian tube towards the uterus. At this stage it will have divided into multiple cells that will form a cluster called a “morula”.

Enamored couple finding out results of a pregnancy test sitting on the bed

Week 4: Implantation – Your first important bond

Once the tiny morula reaches the uterus it is still the size of a tiny seed and now called a blastocyst. The blastocyst’s goal will be to attach to the uterine wall and nourish from it. Upon contact the blastocyst will embed itself into the uterine wall during a process called implantation.

Inside the blastocyst cells are already forming the embryo and grouping themselves according to their purpose. Some will become internal organs, others will become body members and altogether they will ultimately create a little human.

Requirements for food, vitamins, oxygen but also removal of waste will develop at this stage, and so the placenta will begin to form. The placenta will be the main way with which the embryo will be nourished throughout the rest of the pregnancy.


Week 5: We now have an embryo

Week five is considered to be the stage during which the embryonic period begins. The embryo will start to develop extremely fast, and what used to be a bundle of cells will soon start to form important organs and body members.

All the cells in the embryo are now divided into 3 groups which will form the various parts of the little body that is starting to develop. The top layer is the ectoderm. From the ectoderm the embryo will develop a layer of skin, parts of the nervous system, eyes, ears and surrounding tissue. The next layer, known as the mesoderm will provide the building blocks for the muscle, bones, kidneys and reproductive system. The final layer which is located at the center of the embryo is known as the endoderm. The endoderm will create the baby’s bladder, intestines and lungs.

By the end of week five the embryo will probably be the size of a pencil tip.


Week 6: Face starts to develop

Your baby is still developing rapidly during week six. And guess what? Her or his heart could now be beating at more than 110 beats per minute. The neural tube that was forming on the baby’s back, running from the head down is now closing itself.

The basis for some facial characteristics are also forming. Spots and arches are appearing to accommodate the passageways for the eyes and ears as well as the structure of the baby’s jaw.

Tiny little sprouts will bulge a little more where the hand and feet will develop.

Although the upcoming arrival of your baby will not be evident yet on the outside, you will start to feel the effects of pregnancy. This means that you may start experiencing nausea, mood swings, sore breasts and possibly diarrhea.


Week 7: A brilliant mind in the making

This week will mark some important changes for the baby’s head and brain. Brain cells are multiplying at a very rapid rate to form the basis for a brainy future.

Features on the face are taking form as well. Ears and eyes are continuing their development and so are parts of the mouth such as the palate and tongue.

Little paddles are growing where the sprouts were before and they are being segmented to form the different parts of the arms and legs.

At this point you will probably be experiencing most of the pregnancy symptoms that you have heard other mothers complain about. Morning sickness, vomiting, and frequent bathroom runs will become a habit but a lot of it will diminish throughout the pregnancy. Although you probably wont be feeling it, some exercise will help you. Read about the 6 types of physical activities for women during pregnancy and consult with your doctor.


fetal development first trimester

Week 8: Nerve cells are branching and connecting

During the eighth week of fetal development your baby’s nerve cells will start to branch and connect to one another. Its all about the details in this week as the wrists will start to bend, eyelids cover part of the eyes, and taste buds develop on the tongue.

Organs, muscles and nerves are beginning a job that they will carry on, uninterrupted, for many years to come! Her/his heart is powering through all this at more than 150 beats per minute, keeping up with the incredible new developments.

By the end of this week, your baby could reach a length of 16 mm. Its still tiny, but so far from where we started just a couple of weeks back. At this point you have probably made many changes to accommodate the healthy development of your baby.


Week 9: All “main body parts” aboard !

By now almost all the important parts have developed and your baby is ready to gain some weight.

In the ninth week of pregnancy, your baby’s arms are developing their elbows, eyes are covered with paper thin eyelids and wrists and ankles have formed. Toes are also making their appearance and muscles are beginning to twitch.

By the end of this week, the baby might be about 23 mm long. Parts of the genitalia will start to form, but its too early to ask about the sex as it wont be evident through ultrasound.

Your first antenatal appointment should be booked for you to be tested by your doctor and midwife and of course have some of the questions that are pilling up answered.


Week 10: We have a fetus

Your baby is no longer considered an embryo and has now become what we call a fetus. The fetus will be about 31 mm long and its looking more like a baby than ever before.

If you could take a peek you would see details like tiny toes and fingers, and a protruding forehead where the brain has fully developed to carry out its complex functions. The spinal cord is stretching and nerves are branching out of it to make connections with important signal receptors. Tiny little teeth are sprouting under the gums but they wont be visible for a couple more months.

You might be able to feel your womb which has reached the size of a grapefruit right above the middle of your pubic bone. Remember the pair of pants you got last week that fit just right? you probably should have gone for one size larger…


Week 11: Busy baby

Development hasn’t slowed down and although you wont be able to tell the gender yet the fetus has developed ovaries if it is a girl.

Open nasal passages are visible, a tongue, and even nipples. His or her body is straightening itself out some more and mobility in the hands and feet is more than just a muscle twitch. Red blood cells are also forming.

By now the baby might measure up to 50 mm long.


Week 12: Baby’s turning point

Most of the structural parts are almost complete. From here on, body members will fine tune themselves and start training. This means that some muscles in the digestive system will start contracting and organs will begin to function and mature.

The baby’s face has distinct characteristics and the brain has the ability to feel pain. Vocal cords will soon have reached the point where they can produce certain sounds.

In most cases if you visit your doctor at this stage you will be able to hear your baby’s heart beat for the first time.