Congratulations if you’ve just found out you’re pregnant!
Here is the very crucial, first trimester of your baby’s development.
The first trimester will lay important foundations for the rest of your baby’s life.
Find out what will happen in your pregnancy week by week.
Also, you might like to see our pregnancy week by week section, which has each week detailed individually with an illustration of development.
Here’s the first week of pregnancy if you’d like to get started!
The First Week Of Pregnancy
No you are not pregnant yet! In fact your period has just started. Everything begins on day 1 of your cycle when you get your period. Even though your baby has not yet been conceived, ironically, this is still classed as part of the gestation period – the nine months of pregnancy.
So why is this the first week of your pregnancy? The medical profession don’t like unknowns and uncertainties – they prefer proof. It is known that conception takes place approximately 14 days after the start of your period – so to work out an estimated due date, they calculate it from the first day of your last period.
Even at an early stage, there is no exact science to working out your baby’s birth date – only 3-5% of babies are born on their ‘due’ date. So as far as excited family members go, it’s best to just say baby is due, ‘sometime at the end of July!’ for example, to avoid excessive anticipation of a certain day, because there is 97% chance baby wont make a move on your due date!!!
Let’s take a look at what’s happening to your body. Since the end of your last period your endometrium (the inner lining of your uterus), has been thickening in preparation for implantation. This thickening has been caused primarily by an increase in the hormone progesterone. As implantation has not taken place, progesterone levels fall and your body gets rid of this thickened layer causing bleeding – your period.
At the moment, your baby is still a small, single celled egg, hiding in one of your ovaries, completely unaware of what is about to take part!
Pregnancy Week 2
Progesterone levels in your body begin to build. Your uterus starts to thicken, and again starts laying down many extra small blood vessels. Your period has likely ceased by now and an egg in one of your ovaries is ripening, and will soon be released.
Unlike a man who produces new sperm through his life, a woman is born with a lifetime’s supply of eggs already in her ovaries.
Pregnancy Week 3
This is it — the magic week when you conceive!
At this stage you will not know that you are pregnant, but your body will. Your body starts to produce a hormone called Human Chorionic Gonadtrophin (HCG) which you will be able to detect in your urine in a week or so, if you take a home pregnancy test. HCG encourages the ovaries to continue to produce progesterone, preventing your body from shedding the lining of your uterus. Your immune system becomes suppressed so your body wont reject your baby as a foreign object, which is why pregnant women are susceptible to any bugs and colds going around.
Your ovaries will continue to produce progesterone for about 7 weeks, until the placenta takes over. Progesterone is to blame for many of the pregnancy side effects and pregnancy symptoms you will feel – for example the tingling sensation in your breasts and your tender nipples that you will probably start to notice in the next couple of weeks. It also enables your baby to feed from deposits of glycogen. But that’s not all. Progesterone is also responsible for the extra fat your body starts to store. It helps to relax smooth muscle thus preventing premature labour, but it also causes constipation, nausea, reflux, and indigestion. Exciting times ahead!
Your Baby – Week 3 of Pregnancy
So you made love last night with your partner – are you pregnant? Probably not, well not yet anyway. It takes a little while for the sperm to swim to your egg and break through the egg’s outer shell. Out of the 300 million or so of the sperm released by your partner, only one will fertilise your egg – and at that moment of fertilistion, your child’s genetic make-up has been decided – including the sex of your baby. The gender of your baby is determined by your partner’s single successful sperm, which will contain either a male chromosome or female chromosome. As soon as the egg is penetrated, it starts to rapidly divide.
What may surprise you is that an egg is usually fertilised in the fallopian tube. The fertilised egg is swept along the fallopian tubes and down into the uterus (womb) and attaches itself to the uterine wall (implantation). During its journey of around six or seven days, your egg has been continually dividing and is now a cluster of about 100 cells, and is known as a blastocyst.
Pregnancy Week 4
This is when you may first start to suspect you are pregnant. Your period hasn’t arrived (although some women do experience bleeding during pregnancy – see our bleeding during pregnancy article) and you may start to experience some symptoms of early pregnancy. Read our early signs of pregnancy article to find out what early signs you could notice. You might also be wondering when your baby might be due – our due date calculator will give you an estimated date.
Your egg is now well attached to the inside wall of your uterus. It is sending out tiny little hair like tendrils, which will wrap around the abundant small blood vessels in the lining of your uterus and provide oxygen and nutrients to your growing baby. In normal circumstances your blood and the blood of your baby do not mix – you have a separate circulatory system. Exchange of oxygen, nutrients and waste products is made possible due to the closeness of your blood vessels to the blood vessels of the placenta.
Implantation bleeding may occur for some women, resulting in some spotting at around about 10 – 14 days after conception. Some women may think they are starting to get their period, however implantation bleeding is very light and lasts only a day or two.
If you have an indoor cat, you may be wondering about toxoplasmosis, or may not know about it – it’s best to have your partner to change the kitty litter while pregnant due to a parasite which is found in some cats’ faeces, and can be harmful to a fetus. Have a read about what our members think about toxoplasmosis and their cats.
Your Baby – Week 4 of Pregnancy
Your baby is now classed as an ‘embryo’, and it’s heart and a primitive circulatory system rapidly form. Your baby’s neural tube begins to form, which will develop into the nervous system, consisting of the brain, spinal cord, hair and skin. This is an important reason to up your intake of folate (see our list of folate rich foods) as well as take a supplement. It helps the neural tube develop and prevents spina bifida incidence by around 70%. Spina bifida is a birth defect which is where the neural tube does not close completely.
It would be wise to get tested for the MTHFR gene mutation as soon as you can. Many people have this gene mutation, and it impacts how the body uses folic acid (which is synthetic folate). The mutation can cause a range of complications, including miscarriage and loss. There is a simple fix, which includes taking folinic acid instead of folic acid.
Pregnancy Week 5
The tenderness in your breasts and nipples may increase. This is also the week that you may notice some mild stomach cramps and backache. If the cramping is painful then you should seek advice from your Obstetrician or Midwife.
Your Baby – Week 5 of Pregnancy
If you could remove your fertilised egg and have a good look at it, you would see a strange very small shape in the centre. It looks a little like a miniaturised version of a new flower bud on your favourite plant. This tiny little bud will grow to create every organ, bone and muscle in you baby’s body. Your baby’s brain has already started to develop. The placenta and umbilical cord has developed and is helping to feed your new baby. It is responsible for pumping in oxygen, expelling waste, and supplying essential nutrients to your baby during pregnancy. Pretty impressive for a tiny bud only 2 millimetres long, which is about half the size of a grain of rice!
Pregnancy Week 6
You may notice that you need to pee more often, especially in the middle of the night! This will ease in the coming weeks only to return with a vengeance later in your pregnancy! You will also be feeling a little more fatigued than normal – your body is making a baby which is a mammoth effort!
There is a good chance that morning sickness has paid you a visit. Morning sickness affects around 88% of women. Some women will develop hyperemesis gravidarum (severe morning sickness) which usually means a stay in hospital for rehydration. Don’t get mislead by the name, ‘morning sickness’, because it often lasts all day. No one is sure what causes morning sickness but it is suspected that the rising levels of HCG play a major part.
Your Baby – Week 6 of Pregnancy
Your baby starts to look a little like a ‘jelly bean’ and is about 4-5mm long – the size of a grain of rice! Babies at this age are measured from crown to rump (i.e. head to bottom), so this is not it’s full body length including legs.
Your baby already has a bloodstream, and it’s heart, which no bigger than a poppy seed, has started to beat and pump. The heart is not yet fully formed – it only has two chambers instead of the usual 4, but this will soon develop. The baby’s heart beats at around 150bpm (beats per minute) which is around twice the rate of an adult!
If you look closely you would see four little buds which will soon become arms and legs. On the sides of your baby’s head, eyes have started to develop, and over the following weeks the eyes will move into the correct position. The lungs are just starting to appear along with the kidneys and intestines, and the spine has started to form.
Pregnancy Week 7
Not much has changed from last week for the mother-to-be, however morning sickness could be worse. To help:
- Try eating small meals often – avoid going for long periods without food
- Avoid spicy or fatty foods
- Some women find that fizzy drinks help, but this may make gas worse!
- Ginger in any form is also known to help. Try drinking ginger beer, ginger tea or eating ginger biscuits. You can get ginger capsules from health food stores too.
- Some women find that keeping crackers on their bedside table and eating before they get up helps, as well as keeping a pack in their bags or at their desk for the day
- Make sure you are taking enough vitamin B6 (but don’t overdo it – too much isn’t good either)
- There are also many ‘over the counter’ medications you could try if you find morning sickness unbearable, just don’t forget to let the pharmacist know you are pregnant.
Remember that different things will work for different women – you will have to experiment to see what works for you.
Your Baby – Week 7 of Pregnancy
Your baby is now the size of a cherry – around 1.25cm long. His intestines start to develop, along with the eye lenses and liver.
Your baby’s limb buds are now arms and legs, so it’s time for the elbows start to form – soon your baby will start having fun bending and flexing and will soon realise his or her strength – and you’ll know about it!
Your baby’s fingers and toes look like little ridges but will start to develop into tiny digits. Nostrils, lips and a tongue begin to form, along with teeth under your baby’s gums.
Pregnancy Week 8
Your tummy is growing and you may just be able to see the start of your bump. Pimples may start to develop on your face along with darker patches of skin.
Nose bleeds and bleeding gums are caused by the increasing blood volume in your body (about a 30% increase), and a possible lack of vitamin C.
Your Baby – Week 8 of Pregnancy
At a tiny 1.6cms, organs are developing making this a very crucial time for your baby – which is now classed as a ‘fetus’ which is latin for ‘offspring’.
Your baby’s heart is now beating more regularly. The ears, tongue, lips, nose, toes and fingers are forming and you can see baby’s brain and veins through his skin, which is as thin as waxed paper.
Baby’s eyelids are still covered over with skin, but this will later split, forming his eyelids.
Cartilage and bones start to form and the intestines which started off developing in the umbilical cord (yes, seriously!) will soon move into the abdomen. Organs, muscles and nerves begin to function and your baby no longer has an embryonic tail.
Your baby’s limbs are getting longer and it’s elbows and knees are developing.
Pregnancy Week 9
Your Body – 9 Weeks Pregnant
You (and probably your partner!) will probably notice that your breasts have started to grow, due to the development of ducts and glands. The increase in blood supply may cause small blue veins to appear on your breasts. You may consider purchasing a maternity bra to help feel more comfortable – ideally chose a store where you can be properly fitted. See our maternity bra article for more information.
Your Baby – Week 9 of Pregnancy
Your baby is developing rapidly and is now recognisable as a little person. The eyes, nose and ears are recognisable and bones and muscle are visible beneath the thin translucent skin. Your baby also starts to move but these movements are small and you will not be able to feel them yet. Your baby is feeding from the placenta which has been developing over the past few weeks. Ankles have formed and your baby can bend his arms with his little elbows.
Ovaries or testes are well developed but at this stage it is not yet possible to determine the sex.
Your baby measures approximately 2.3-2.5cm long and isn’t quite 2 grams.
Pregnancy Week 10
You may be getting some crazy, wild mood changes, which is caused by the rapidly increasing hormones. Constipation can also be a problem at this time, which is caused by progesterone relaxing the bowel and intestine, slowing down the passage of food. When this happens your body removes more water from your stools causing them to harden. To help relieve this ensure that you are drinking plenty of filtered water (2-3 litres a day). A high fibre diet (from fresh foods, not cereals and breads which can make constipation worse) will also help. Wind or gas often increases in pregnancy. Find out more about gas during pregnancy.
Your Baby – Week 10 of Pregnancy
Baby can now make small un-coordinated movements. Fingers toes and joints are now fully developed and your baby even has fingernails and hair! The nervous system is starting to develop along with the large muscles and the digestive system.
Eye colour is now determined and the eyelids are fused shut until early in the third trimester, as the the irises develop. Your baby’s head is about half it’s body length!
Your baby measures approximately 3cms long and weighs around 4 grams.
Pregnancy Week 11
You become more sensitive to smells. Some smells will make you feel sick. Your temperature will increase causing you to feel hot and sweaty at times. Your emotions may still be a little wild and erratic but should start to calm down soon. You may get a ‘linea nigra’ (Latin for ‘black line’) on your belly which is a purple/brownish line down the middle of your belly to your pubic area, about 1cm in width. It’s known that hormones cause the linea nigra but not known why it forms in the vertical line that it does. The linea nigra is more common in dark skinned women, but not uncommon in fair skinned women.
Your Baby – Week 11 of Pregnancy
Major organs are now formed and functioning. Your baby starts to pass urine from it’s kidneys. It is also able to suck and swallow and has also started to make small voluntary movements. It’s fingers and toes have fully separated and baby spends his spare time kicking and swimming!
Everything your baby needs in now supplied by the placenta. Your baby’s heartbeat can now be heard with a doppler.
Your baby measures approximately 4cms long and weighs around 7 grams.
Pregnancy Week 12
Your uterus has now grown out above your pelvis taking some of the pressure of your bladder. You should notice that you don’t need to go to the toilet quite as often. For now, anyway!
It’s a great time to treat yourself to a new pair of pants or a skirt etc – you have probably put away many of your pre-pregnancy clothes now and have very little clothes that fit or feel comfortable. Some women may feel down about their appearance at the end of the third trimester – they know they are pregnant and have a little bump, but to the outside world, they may not realise it’s a baby bump! So women may feel very self conscious, especially if hormones haven’t been kind to your skin too! So if the finances allow, treat yourself and you will feel so much better.
Your Baby – Week 12 of Pregnancy
Your baby’s sex organs are now distinguishable, but still incomplete. Your baby’s eyes are almost in the correct position in relation to it’s head, as are it’s ears.
The lungs are developing and primitive breathing can be seen. Vocal cords begin to form. The amniotic fluid that your baby swallows is now passed out through it’s bladder.
Your baby’s bones, which until now were soft, are starting to harden, including the ribs and spine. It’s arms are in proportion with the size of it’s body. Toes and fingers are formed.
Movement will not be felt yet but your baby is still kicking away, and can now curl it’s toes, rotate it’s ankles and wrists, press it’s lips together and make facial expressions, like frowning and smiling.
Your baby measures approximately 4-5.5cms long and weighs around 14 grams.
Pregnancy Week 13
Welcome to the last week of the first trimester!
Stretch marks may start to appear on your breasts, stomach and thighs. You may feel an ache or pulling sensation in your tummy. This is caused by the ligaments that support your uterus stretching. A lot of the discomforts that you have been feeling up until now start to disappear. However for some women these symptoms can continue until week 20. The next 3 months are usually the most comfortable. Some women are a little concerned about this reduction in symptoms, often thinking that it a sign that something is wrong.
Your Baby – 13 Weeks of Pregnancy
Your baby now has fully functioning kidneys and starts to pass urine regularly. It is also able to suck and swallow and it’s neck is getting longer. The spleen has started to develop. And your baby is now producing bone marrow. Movements increase but it is unlikely that you will be able to feel these movements, especially in a first time pregnancy. Baby even has it’s unique set of fingerprints.
You’ve gotten through a crucial part of your baby’s development. All the forming and foundations have now been laid and the main thing that remains is maturity and growth of the baby. It’s been a very busy trimester for your body and your baby, so now it’s time to grow and mature ready for birth!
Your baby measures approximately 7-8cms long and weighs around 23 grams.
DID YOU KNOW: If you are pregnant with a girl, there are now around 2 million eggs in her ovaries… but there will only be one million by the time she’s born. Her eggs will decline she gets older – by the age of 17, she will only have around 200,000 eggs.
Enjoy the second trimester – it’s usually the most favourite trimester for pregnant women. The bump is finally noticeable, but not too big and uncomfortable, you get the ‘glow’ and your risk of miscarriage has dropped dramatically. Your moods tend to be more settled and energy much better than in the first trimester – so we hope you enjoy your next 13 weeks!