If you're newly pregnant (or trying to become pregnant), you'll start to hear a lot about "trimesters". It might become one of the most used or read word for you during this time. So, what does it mean?
It simply means each three-month block of your pregnancy. So, we've broken it down into need-to-know features from each trimester, for both baby and you.
First Trimester – weeks 1-12
Baby (we'll just call him "he")
- He grows very quickly – from 1g at four weeks to about 15g at 12 weeks.
- At first the embryo floats in a bubble that will become the amniotic sac. All nutrients come from an attached “yolk sac”.
- By the end of the first month, the embryo has a recognisable head, nervous system, body and tiny limb buds, which will grow into arms and legs.
- The major organs are forming. The heart starts to “flutter”, and then beat.
- At 12 weeks facial figures can be distinguished.
- Towards the end of the third month, the kidneys begin to secrete urine. Soft nails form on the fingers and toes and twenty buds; that will become baby teeth, appear in the gums.
- He starts to move, stretching and kicking, long before you can feel movement.
Mum
- First symptoms can include sore breasts, morning sickness, exhaustion, increased urge to urinate, constipation, and headaches.
- A plug of mucus is formed in your cervix as protection.
- Your metabolism, heart rate, circulation and breathing rate all increase and you may feel light-headed and dizzy.
- The areola (skin around your nipples) darkens.
- Mood swings can be extreme and you may feel indecisive.
- You may get pimples or acne.
- You may experience a drop in libido.
- Your breasts may increase in size and your waist starts to thicken.
Second Trimester – weeks 13-28
Baby
- The placenta takes over as your baby’s source of food and oxygen.
- After 14 weeks your baby’s heartbeat can be heard with a sonic aid.
- At 16 weeks he resembles a tiny human being.
- He starts to have a pattern of active and resting times.
- He can hear and may “jump” if there are sudden loud noises.
- As early as 18 weeks his eyes will open and he can make facial expressions.
- At 24 weeks major organs work, but lungs and digestive systems need further development.
- Scans now show babies from 26 weeks exhibiting a whole range of behaviours including scratching, hiccupping, and thumb sucking.
Mum
- You will feel the first movements – often a sensation like butterflies known as “quickening”.
- Your waistline will disappear, and you will “show” from about week 16.
- The sickness and other symptoms of early pregnancy will decrease or disappear but heartburn may set in.
- Mood swings are less extreme – and you are likely to feel calmer and more positive.
- You will probably feel more energetic. Your libido returns, and may even increase.
- You may begin to experience backache as your shape changes, and hormones cause your pelvic joints to soften and your muscles to relax.
- Your appetite tends to increase but your digestion becomes sluggish.
- Your body temperature may rise and you may sweat more.
- You may get leg and foot cramps – particularly at night - and your feet and legs may start to swell.
Third Trimester – weeks 28-40
Baby
- He starts to make breathing movements.
- His skin becomes smoother.
- His nails and hair grow longer and his skull hardens.
- He lays down fat ready for labour and the first few days of life. He should double his weight in these last three months.
Mum
- Your nipples may begin to leak colostrum, the first antibody-rich milk that your body produces.
- Pelvic pains and aches increase.
- Braxton Hicks (practice) contractions begin.
- You start to become more tired and uncomfortable, and may have difficulty moving about. You may feel restless and have difficulty sleeping.
- You need to wee more again as baby’s head moves down into the pelvis.
- You may feel a surge of increased stamina and energy as the delivery date draws near.
You can read more about each trimester in this brilliant ebook
From Bump to Birth.
Louise Ní Chríodáin co-authored ebook From Bump to Birth with Margaret Hanahoe, Assistant Director of Midwifery at the National Maternity Hospital. It’s a no-nonsense companion for pregnancy and labour, packed with essential tips and advice from midwives and mothers. A second ebook “After Birth”, a guide to minding mum and baby in the first weeks, will be along shortly. You can find more of their tips and advice on the site: Bump to birth to baby. 
You can read more about each trimester in this brilliant ebook From Bump to Birth.
Louise Ní Chríodáin co-authored ebook From Bump to Birth with Margaret Hanahoe, Assistant Director of Midwifery at the National Maternity Hospital. It’s a no-nonsense companion for pregnancy and labour, packed with essential tips and advice from midwives and mothers. A second ebook “After Birth”, a guide to minding mum and baby in the first weeks, will be along shortly. You can find more of their tips and advice on the site: Bump to birth to baby.
