Pregnancy - Week by Week
Pregnancy - Week by Week

First trimester

  • Not much to see but plenty going on inside, and lots to think about. As your baby begins to develop and her brain and spinal cord start to form, you and your partner will be adjusting to being pregnant and to all the imminent changes to your life that a baby brings.

  • Physical changes include larger, more tender breasts; more sensitive nipples; tiredness; constipation; passing urine more often; changes in smell and taste; mild dizziness; going off foods that you previously enjoyed; and morning sickness (at any time of day).

Weeks 1-2

Although you haven’t yet conceived, you’re officially pregnant from the first day of your last period, as this is when your pregnancy is dated from. Most women tend to ovulate around 12 to 16 days before their next period so, in an average cycle, that’s towards the second week after your period started. Once your egg is released from your ovary, it will survive for 12 to 24 hours – that’s the perfect time to start trying for your baby!

Week 3

Your egg and your partner’s sperm can meet in as little as 45 minutes after ejaculation. Once the sperm breaks through the egg’s protective shell, and merges his genetic material with yours, they begin to create your baby. Though it’s hard to identify exactly, from the moment of fertilisation a pregnancy lasts for 266 days.

Week 4

The original sperm-egg cell is now a fluid-filled ball of hundreds of cells. By around seven days after fertilisation it should have begun burrowing into the lining of your womb. By day eight or nine, your future baby has begun sprouting fronds called chorionic villi, seeking nourishment. Although it would fit on the head of a pin, it’s impressive, producing the human chorionic gonadatrophin hormone that stops your womb lining shedding in a period.

Week 5

She looks like a tiny bubble as her miniature yolk sac and amniotic sac are now visible. The different cells for each major tissue type – skin, intestines, nervous system and bones – have been jockeying for position, and the different parts of the body are already starting to form.

Week 6

Her heart is only about the size of a poppy seed but it is beating on its own. Her neural tube (future spinal cord and brain) has formed. In rare cases, the ends of this tube don’t close, resulting in spina bifida. She has 125,000 cells – and that is quite an achievement when you think that just a fortnight ago she only had 64 cells!

Week 7

The size of a small pea, your baby is growing at a rate of 1mm a day. All her vital organs are now in place – heart, liver, kidneys, pancreas and thyroid. Tiny eyelids have begun forming over her eyes. Her umbilical cord is in place, containing two arteries and a vein, which connects to the placenta, her nourishment source.

Week 8

Her fingers and toes are developing with webbing between them. Her tiny skeleton is fully formed but is made from soft cartilage instead of bone. Her yolk sac has disappeared as she no longer needs it for food, and her tail has almost vanished. She’s already begun her physical training program by making little twitches.’

Week 9

Your baby’s arm and leg bones are lengthening, and she’s making definite movements, though you can’t feel them. If you’re having a boy, the first signs of a penis emerge around now, but you’d need a very sensitive scan to spot it.

Week 10

Your child is now about the size of a large strawberry. She’s making arm and leg movements, though you can’t feel these yet, as well as chest movements, which may be practice for breathing. She is already picking up on your emotions (such as stress, calm and happiness) through the hormones that cross the placenta.

Week 11

Your baby is getting more and more active. If you could peep inside your womb, you’d see how graceful her movements are. She’s now graduated from being an embryo to being a foetus. The name means “little one”, and your carers will refer to her as such until she’s born.

Week 12

You’ll usually be offered an ultrasound scan to check the position of your placenta, your baby’s position and probably her age/size. Some research suggests babies dislike ultrasound scans, that they try to duck headfirst into the pelvic bowl to avoid them, and that the ultrasound waves may even leave them with a headache.

1st Trimester Pregnancy Guide

Take a detailed week by week look at the 1st trimester in our 1st Trimester Pregnancy Guide

Second trimester

  • This is generally the most comfortable and enjoyable time of a pregnancy. Your belly begins to grow – finally, you look pregnant! As the symptoms of early pregnancy disappear (though some can linger), the chances are you look and feel great. As hormones settle down, you should feel calmer and less susceptible to mood swings than in the first trimester (again, no promises!).

  • Expect changes to your hair, skin and nails. Stress incontinence (as pelvic floor muscles stretch), heat rashes and itchy skin are common complaints, and you’re five times more likely to get thrush now than when not pregnant.

Week 13

She’s extending her fingers, yawning and sucking her thumb. Some unborn babies are so keen on this pastime that they’re born with calluses on their thumbs. She won’t stay still for more than about 15 minutes at a time, day or night, until around week 20.

Week 14

If you were able to touch your baby very gently on her cheek, she would turn her head and start searching as if reaching for a breast to suckle from. She is beginning to perform rhythmical movements with her arms and legs.

Week 15

You may be offered an amniocentesis test to check for chromosomal problems such as Down syndrome. Your baby may notice the needle, even though her eyelids are still shut, and react with alarm, so try to stay calm yourself and to send calming messages in your head to your baby.

Week 16

Your baby would now fit into the palm of your hand. She’s beginning to make her first eye movements and may be starting to respond to sound, even though her ears aren’t yet fully formed. She probably picks up sound via vibrations through her skin. She’s starting to explore the inside of your uterus with her hands.

Week 17

Your baby is now about 16cm long and weighs about 175g. She’s covered in fine, downy hair called lanugo, which will mostly have disappeared by birth. Her movements are becoming more vigorous.

Week 18

She starts practising making sounds. The idea that unborns could do this was once dismissed as a sentimental fancy, but research has shown foetuses on ultrasound scans using their tiny larynxes to produce sound vibrations.

Week 19

Your baby is around 18cm long and is developing the fine neurological pathways and skills she’ll need after the birth. She is now practising whole-body movements (such as back flips and rolls) and actions (like kicks, punches, sucking and breathing movements).

Week 20

She’s reached the halfway mark. She can now reach out with her hands for a light source panning across your tummy (from a strong torch beam), even though her eyes are fused shut. You can safely do this at home – lift your top and shine a torch onto your bump.

Week 21

Doctors usually offer to scan your baby to check the major organs, see how many babies you’re having (twins are a one in 80 chance), make sure it’s growing normally and find out what sex it is. They won’t reveal the sex unless asked specifically, but many mums have their own ideas anyway!

Week 22

In Thailand, the Hua Chiew Hospital now starts playing the unborn baby tapes of her parents’ voices, calling the baby’s name, talking to her and playing gentle music to stimulate her brain and nervous development. Do you ever find yourself talking to your baby out loud? You’re not alone – many mums-to-be do!

Week 23

Your baby measures around 19cm. Her skin is becoming less transparent and her little fingernails are fully formed. And she even notices when you make love! A Scandinavian study found unborns’ heart rates either shot up or slowed whenever their mums had an orgasm.

Week 24

Your most rapid weight gain starts to happen about now. And your baby can start to play her first games with you! According to research by a US obstetrician, you can teach baby to kick in response to you patting your tummy and saying, “Kick, kick!” When she responds, gently rub the area and say, “Good baby, kick again!” This kind of play helps to stimulate her neurological development.

Week 25

Her ears are now structurally complete, which suggests she may be able to hear more complex sounds, like voices, better. If your partner and any older siblings try talking to her through your bump from now on, the chances can increase that she’ll be born knowing their voices.

Week 26

About 23cm long and weighing about 0.9kg, your baby could begin developing a sweet tooth now as her tastebuds are starting to form. Research as far back as 1937 shows that if something sweet is introduced into the amniotic fluid, an unborn baby’s swallowing rate increases.

2nd Trimester Pregnancy Guide

Take a detailed week by week look at the 2nd trimester in our 2nd Trimester Pregnancy Guide

Third trimester

  • You may feel great or you may feel dreadful; you may be enormously excited about the impending birth or terribly anxious. Or all of the above.

  • Likely discomforts include backache, breathlessness, heartburn and leg cramps. Your breasts become heavier and your nipples enlarge.

Week 27

Your baby is growing fast, and is now around 25cm long and 1.1kg in weight. Her eyes have opened and, like all babies, are blue, as the irises don’t acquire their final colour until after birth. Her nostrils are open and she’s practising breathing movements.

Week 28

She’s now taking language lessons from you. In 1975, a study used sophisticated audio technology to analyse the cries of newborn 28-week-old premature babies. Researchers were startled to find the premature babies were copying their mother’s basic speech patterns.

Week 29

She’s about 28cm long and 1.4kg in weight. Her eyes can move and she’s becoming more sensitive to light. If you were to sunbake with your tummy uncovered, the light would appear to her as a warm, orange glow.

Week 30

Your baby is moving often now because she’s the strongest she’s ever been and she still has plenty of room in the womb. Many women find that their unborn babies are at their most active at around midnight, and this carries on for many weeks after they’re born while you’re trying to teach them to tell the difference between night and day.

Week 31

She’s now becoming a little plumper and, although she still appears thin, you can no longer see the tracery of blood vessels beneath her skin or the shadowy images of her growing bones. She’s laid down around 50g of fat, which may not sound like much, but it represents 3.5 per cent of her total body weight (the average woman’s body is 27 per cent fat).

Week 32

She is now fully formed, with her head in proportion to her body at long last. She even has eyebrows and eyelashes! Your baby is busy building up her immune system, borrowing from you, to protect her from contracting a wide range of diseases once she’s born.

Week 33

According to French research, your unborn baby could now be taught to recognise a simple piece of music and will respond to it after birth if it’s played daily over the next month. Usually, the music that calms you will also soothe your unborn baby, so try popping on your favourite CD when
she seems particularly restless.

Week 34

She’s now about 33cm long and weighs around 2.3kg. She has grown so much that she’s beginning to find it a tight squeeze and so will be kicking and punching less, although she wriggles and rolls, and tries to stretch more. By about now she should be positioned with her head downwards, in preparation for the birth.

Week 35

Your baby’s little legs and arms are plumping up nicely. She’s exercising her kidneys by getting in some impressive weeing practice, urinating about 115 teaspoons’ worth every day into the amniotic fluid. The waste products in her urine are being filtered through the placenta into your bloodstream, where they are then dealt with by your own kidneys.

Week 36

If you’re one of the one in 80 mothers having twins, it is usual for them to be born between 35 and 37 weeks, instead of 40. A powerful closeness between your babies has already developed. In the early 1990s, an Italian psychologist, Dr Alessandra Piontelli, filmed unborn twins hugging, stroking and patting each other’s faces in the womb.

Week 37

Now about 40.5cm long and weighing around 2.75kg, your baby is steadily putting on weight and looks like a newborn. Her head could engage this week, moving down into your pelvis into the ready-for-birth position. If she’s landed bottom-first in a breech position, she may still turn around. However, if she stays breech, her birth is likely to be by caesarean.

Week 38

She’s spending 60 per cent of her time asleep. Research has revealed that Rapid Eye Movement (REM), which indicates dreaming, takes place in unborn babies from 23 weeks on. Dreaming also encourages brain development, which occurs at a rapid rate in these last few weeks.

Week 39

Most of your baby’s lanugo is gone and her umbilical cord is just about as long as she is. She has no fewer than 300 bones, some of which will fuse as she grows. Antenatal psychologists suggest mothers could help to prepare their unborns for the big surprise of birth, and some obstetricians advise lightly spraying your belly with cold water each day from now on to help them get used to colder temperatures.

Week 40

By now some 15 per cent of your baby’s body is fat and she has a total length of about 48cm. Several controversial studies suggest that babies may remember being born. They appear to recall the birth process, and even the first words that were spoken to them, under hypnosis.

3rd Trimester Pregnancy Guide

Take a detailed week by week look at the 3rd trimester in our 3rd Trimester Pregnancy Guide

Sources: Your Pregnancy Bible, consulting editor Dr Anne Deans (Penguin/Viking, RRP $45), and Birth by Catherine Price & Sandra Robinson (Pan Macmillan, RRP $39.95).

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