First trimester: amazing pregnancy facts

Being Pregnant – 09 Feb 24 By Sanchia Pegley

Your body is doing incredible things!

Pregnancy is dividing into three trimesters and the first trimester is weeks 1 to 12. The first 12 weeks is an exciting time – a rollercoaster of emotions, physical changes and much more that only you can feel, and no one else can see (yet)!

You have probably already started thinking about baby names, starting school, where you’ll spend the long summer holidays! You might also have the occasional little freak out or panic as you move into this lifechanging time. This is completely normal if this your first time (or even if it’s your second or third and you’ve thinking about how to juggle a growing family).

Here, you can learn 18 incredible facts about the first trimester of your pregnancy.

18 facts about the first trimester

It takes 24 hours for sperm to fertilise an egg

1.It may only take one sperm to fertilise an egg, but when you have sex around 100,000 of your partner’s swimmers surf into your cervix to have a shot at making a baby.

2. 24 hours is the time it takes for the sperm to enter the egg and fertilise it. Your pregnancy has begun, although you don’t even know it.

3. About 2% of all pregnancies involve twins. Identical twins occur when one egg is fertlised by one sperm, then divides into two separate zygotes (the cell that becomes a baby). Non-identical twins are conceived when two separate eggs are released and fertilised by two separate sperm. Non-identical twins run in families, but identical twins appear to be completely random.

4. A four-week-old embryo is the size of a poppy seed.

Young long-haired couple, smiling and leaning into each other so their foreheads touch — The first trimester is an exciting time with lots of changes. *(Image: Getty)*

Chromosomes determine the gender

5. Boy or girl? Your partner is the one who decides. All eggs carry a single X (female) chromosome, while sperm carry either an X or a Y (male) chromosome. If an X sperm fertilises your egg, it’s a girl; if a Y makes it in, you’re having a boy.

6. Just six weeks into your pregnancy, your baby already has a heartbeat… yet she’s still only as big as a lentil.

7. Jeans feeling tight? At six weeks, your uterus has already expanded from the size of a plum to the size of an apple.

8. By seven weeks, your baby already has the three distinct regions of the brain that will form the basis of all her thoughts and actions: FOREBRAIN: this part of the brain is responsible for problem-solving, reasoning and memories; MIDBRAIN: directs electrical impulses from your baby’s body to the right areas of her brain; and HINDBRAIN: controls physical activity like breathing, heartbeat and muscle movements.

View looking over woman's shoulder as she looks at scan photos of early pregnancy — Your baby’s heartbeat is visible from about 8 weeks. *(Image: Getty)*

Tiny fingernails are forming!

9. At eight weeks, your baby is officially classed as a foetus, which means ‘little one’ in Latin. Aww!

10. If you have a scan at eight weeks and a heartbeat is visible, the risk of miscarriage falls to just 2%.

11. By the 10th week, your baby is just the size of a peapod, but they already have recognisable eyes, ears, nose and mouth, all four limb buds, plus fingers and toes. They also have tiny fingernails and the bubs for the milk teeth.

12. If your unborn baby is a thumb-sucker, their preferred hand at just 10 weeks could reveal whether they will be left- or right-handed. A Belfast University study showed that at the age of 12, all the children who had sucked their right thumbs in the womb were right-handed, and two-thirds of those who’d sucked their left thumb became lefties.

Black and white ultrasound image of a foetus sucking their thumb — Thumb sucking in the womb may indicate whether your bub will be left or right handed. *(Image: Getty)*

Baby’s reflexes are developing

13. At 10 weeks, your baby can already respond to touch! If you prod your tummy now, they’ll wriggle away – not that you can feel it… yet.

14. Your baby’s heart beats 110-160 times per minute – twice as fast as yours.

15. All of your baby’s major organs – including heart, lungs, kidneys, brain and intestimes – are formed and full functional by 10 weeks. Now they just have to do some serious growing!

16. Your baby’s reflexes begin to develop at about week 12. If she accidentally brushes her face with her arm or leg, her lips will purse as if to suck, and if she touches her eyelids, she’ll blink.

17. Most women have a eggcupful of amniotic fluid at the end of their first trimester, and about a bottle of wine’s worth by the end of their pregnancy.

18. At 12 weeks, your baby weighs about the same as an empty soft drink can.