first trimester

Baby’s development in the first trimester (weeks 0 – 12)

Pregnancy usually lasts 40 weeks, counting from the first day of your last period and is grouped into three trimester. Find out everything about your baby’s development in the first trimester.

Week 1 – 2

The weeks of your pregnancy are calculated starting from the first day of your last period. This means that in the first two weeks or so, you aren’t actually pregnant. During this time your body prepares itself for ovulation, as any other month.

Conception usually takes around 2 weeks after your period during ovulation. When you ovulate, an egg gets released from the ovaries around two weeks after the first day of your period, depending on the length of your menstrual cycle.

Week 3 – 5

During the third week, your fertilised egg moves along the fallopian tube towards the womb. The egg begins as a single cell, which divides again and again, and by the time the egg reaches the womb, it has grown into a mass, that consist around 100 cells or more. At this point it’s classified as an embryo. Once the embryo reaches the womb, it burrows into the lining of the womb. This phase is called implantation.

During the 4th and 5th week, the embryo grows and develops within the lining of the womb. The embryo is attached to a tiny yolk sac  that provides nourishment and is surrounded by fluid inside. It’s the outer layer of this sac that develops into the placenta. A few weeks later, the placenta will be fully formed and will take over the transfer of nutrients to the embryo.

During the 5th week, you’ll have noticed that you missed your period. By this time, the baby’s nervous system is already developing, and the foundations for its major organs are in place. At this stage, the embryo is around 2mm long.

The embryo’s outer layer of cells develop a groove and folds to form a hollow tube called the neural tube, which will eventually become the baby’s brain and spinal cord. The heart is also starting to form. In the beginning it is only a simple tube-like structure, but at this stage the baby already has some of its own blood vessels and blood begins to circulate. A string of these blood vessels connects the baby and mother. This bond later on will be known as the umbilical cord.

Week 6 – 7

By the 6th week of  pregnancy, the embryo has developed a large mass where the heart is and a bump that will become the brain and the head. At this stage, the embryo is curved and has a tail.

The limbs are already visible in the form little swellings as they’ve started developing. Little dimples on the side of the head will become the ears, and there are thickenings where the eyes will be. By now the embryo is covered with a thin layer of see-through skin.

By the 7th week, the embryo has grown to about 10mm. The brain is starting to grow, that results in the head growing faster than the rest of the body. The inner ear starts to develop, however the outer ear on the side remain the same dimples.

Cartilages start to form inside the limbs, which are going to be leg and arm bones later on, and the shape of the limbs start to flatten out, to later form the hands. Nerve cells continue to multiply and develop as the the nervous system starts to take shape.

Week 8 – 9

By the time you’re 8 weeks pregnant, the baby is called a foetus. The legs are getting longer, but the different parts aren’t properly distinct yet.

The foetus is still inside its amniotic sac, still receiving nourishment, and the placenta is continuing to develop, so that it can attach to the wall of the womb later on.

By the 9th week, the baby’s face is slowly forming. The eyes are bigger and some pigmentation can be found in them. The a mouth and a tongue with tiny taste buds have also started developing. Tiny ridges identify where the fingers and toes will be on the hands and toes, although they haven’t separated out yet. Most major internal organs continue to develop. By this stage the baby has grown to about 22mm long in size.

Week 10 – 12

The ears and ear canals are starting to develop. The jawbones are forming and already contain all the future milk teeth.
At this stage, the heart has fully developed and the baby is making small movements that can be detected on an ultrasound scan.

During week 11, the baby grows quickly and the placenta is rapidly developing until it’s fully formed by week 12. The facial bones are formed, and the eyelids are closed. They won’t open for a few months yet.

Your baby’s head makes up one-third of its length, but the body is growing fast too. The fingers and toes are separating, with fingernails present. The body itself is also starting to straighten out.

The foetus is fully formed by the 12th week. All the organs, muscles, limbs and bones are in place, and the sex organs are well developed, although the sex of the baby can’t be told yet.  The baby’s skeleton is made up of cartilage and it starts to develop into bone. From now on, the baby only has to grow and mature. You won’t be able to feel the baby’s movements yet, however rest assured, there’s plenty of movement!

Credit: NHS.

More you might like

Baby’s development in the second trimester
How to cope with pregnancy swelling
Aches and pains in pregnancy you can’t ignore


Q. I’m would like to start an exercise programme that will benefit my emotional health as much as my physical health, but I don’t know which type of class would be best. Should I consider choosing from yoga, pilates, tai chi, or could you recommend a class, please?

A It’s great that you have decided to get into exercise. The benefits to you are going to be great. You’ll sleep better, have more energy, better skin, reduced stressed, not to mention all the amazing physical benefits of your clothes fitting better, and looking healthy, trim and toned! My advice to you would be to try them all. Even if some don’t offer pay-as-you-go sessions, if you get in touch directly with the instructor, they will almost always let you try it out first to see if it’s for you. All of the above things that you mentioned are great for mental health, so it really will be a personal preference as to which you go for. On top of the classes you mention, all forms of exercise will give you great mental rewards so consider the not so obvious interval training sessions, bootcamp, and circuits too, as you will also feel on top of the world after a class like that.


Ask Sarah

Q I’ve heard a lot about the Paleo diet and as I am very interested in reducing the amount of processed foods and grain based meals my family eats, we are considering following this diet. From what I read it seems to be a back-to-basics type of eating. Is a Paleo diet safe for children? My kids are aged seven and nine.

A The Paleo diet is one of the most fashionable diets around at the moment. It is also known as the ‘caveman diet’ and is based on cutting out processed foods, starchy foods like bread and potatoes and eating more meat, vegetables and fruit.
As fad diets go, it is not the worst but there are some good and bad sides to it. Reducing the amount of processed foods we eat is always a good idea and by doing that you will usually reduce the amount of fat, salt and sugar you eat, which is a good thing! The problem with the Paleo diet is that it also cuts out dairy (on the basis that cavemen didn’t drink milk) and this means that the diet is very low in calcium. For this reason it is really not suitable for children who do need a lot of calcium for growing bones. How did cavemen manage without dairy? They ate a lot more food than we do (up to 10,000 calories per day compared to the 2,000 most of us eat). By eating that amount of food they were able to pick up just enough calcium from green vegetables and seeds. To put it in perspective, you would need to eat 16 servings of broccoli a day to get all the calcium you need. This is easier to do if you eat 10,000 calories per day rather than 2,000.
The other problem with the paleo diet is that it is not entirely based in science. Many of the Paleo diets out there say you should not eat wheat, even though we know that cavemen did in fact eat wheat and other grains. These diets also don’t recommend that you eat blubber and the big lumps of fat that were also a large part of the caveman diet!
A final problem is that many Paleo diets encourage people to cut out beans and lentils and to get their protein from meat and fish instead. Many studies over the last few years are clear that eating too much animal protein is linked with more cancer and heart disease. Eating some vegetarian meals based on beans and lentils is a great way to get your protein without always going for meat.
Is this a diet we should follow? I think there is a lot we can learn from the Paleo diets. We could all do with eating less salt, sugar and processed foods and adding in more nuts and seeds as well as more vegetables. However, I think following a strict Paleo diet could lead to low levels of calcium and vitamin D and so it is not suitable for children or teens and adults would need to think about a calcium supplement.