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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.
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.
About 2% of all pregnancies involve twins. Identical twins occur when one egg is fertilised 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.
A four-week-old embryo is the size of a poppy seed.
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 anX sperm fertilises your egg, it's a girl; if a Y makes it in, you're having a boy.
Just six weeks into your pregnancy, your baby already has a heartbeat… yet she's still only as big as a lentil.
Jeans feeling tight? At six weeks, your uterus has already expanded from the size of a plum to the size of an apple.
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.
At eight weeks, your baby is officially classed as a fetus, which means 'little one' in Latin. Aww!
If you have a scan at eight weeks and a heartbeat is visible, your risk of miscarriage falls to just 2%.
By the 10th week, your baby is the size of a peapod, but she already has recognisable eyes, ears, nose and mouth, all four limb buds, plus fingers and toes. She also has tiny fingernails and the buds for her milk teeth.
If your unborn baby is a thumb-sucker, her preferred hand at just 10 weeks could reveal whether she will be left- or right-handed. A Belfast University study showed that at the age of 12, all of 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.
At 10 weeks, your baby can already respond to touch. If you prod your tummy now she'll wriggle away – not that you can feel it… yet.
Your baby's heart beats 110–160 times per minute – twice as fast as yours.
All of your baby's major organs – including heart, lungs, kidneys, brain and intestines – are formed and fully functional by 10 weeks. Now she just has to do some serious growing!
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.
Most women have about an eggcupful of amniotic fluid at the end of the first trimester, and about a bottle of wine's worth by the end of their pregnancy.
At 12 weeks your baby weighs about the same as an iPod Shuffle.