• Penni from Up Up n Away


Updated: Mar 12, 2021

Twins account for around 90% of multiple births and far outnumber triplets or quads in the multiple birth stakes. Currently in Australia almost 2% of all babies born come in multiples.

Double trouble! Once you have found out that you are expecting twins it can very exciting. It can also be scary as you think about how you will juggle two babies at once.

The following information aims to help you to understand more about twins and offers some ideas about how to care for them. Most of the information also applies to triplets and other multiple births.

How will I know if I’m having twins?

You may suspect you are having twins long before they are positively diagnosed. The pregnancy hormone, hCG is being produced in massive quantities and its effects on your body become very evident. One of the first symptoms is likely to be extreme nausea and the inability to keep any food down. You’re likely to be able to tick all the boxes for early pregnancy symptoms, but increase them tenfold - smells are more acute, your bladder seems miniscule, you’re absolutely exhausted and your breasts have taken over your chest.

Pregnancy is usually not obvious until after the 12th week when the uterus starts lifting up out of the pelvis. Two babies, however, take up double the space so it’s likely you’ll “show” much sooner and often a little round bulge is visible long before the end of the first trimester.

Another give away sign is lots of movements, felt earlier than normal. Quickening is not generally felt until around 16 weeks by first time mothers and as early as 14 weeks for those who’ve been pregnant before. But with twins, those tiny first movements can be very clear as they fill up the uterus much earlier than one baby and are in contact with the uterine wall as they bounce and flit around.

You may also find out from having an ultrasound and see two babies on the screen. Sometimes pregnant mothers don’t know they’re having twins until the 18 week screening ultrasound; others as early as 12 weeks. It’s possible to see on ultrasound at 12 weeks or earlier which type of twins a woman is carrying.

Finally, a twin pregnancy can be detected through Doppler; when two separate heartbeats are heard.

How are twins formed?

Identical twins (or monozygotic twins)

  • Identical twins occur when a single sperm fertilises an egg, and then, at a very early stage, the fertilised egg divides into two and starts forming two babies.

  • Identical twins have the same genes, so they are the same sex.

  • Some of these twins have their own separate placenta (afterbirth) and sac to grow in the mother’s uterus (womb) but many share the same placenta and sac.

  • Monozygotic twins may be quite different sizes at birth, but they become more alike with time. They are often hard to tell apart when they are older.

  • Identical twins do not usually “run in families” and it is not known why monozygotic twins occur.

  • Identical twins happen about once in every 250 live births.

Non-identical twins (or dizygotic twins)

  • Non-identical twins are also sometimes called fraternal twins. They happen when two separate eggs are fertilised by two different sperm so that two embryos (the beginnings of a baby) are formed.

  • Each has its own separate place in the uterus and separate placenta and sac.

  • They may be the same sex or different sexes.

  • Dizygotic twins are often similar at birth, but they become less alike as they get older, as do other (different age) brothers and sisters.

  • Dizygotic twins are more likely to happen when there are twins in the mother’s family, or if the mother has been having fertility treatment. If a mother is a non-identical twin, she has about a 10% chance of having twins herself. (A mother of twins who is not a twin herself, has about a 5% chance of having another set of twins). If the father is a twin, this does not make it more likely that the parents will have twins.

  • About two births in every hundred are dizygotic twins. There has been a rise in the number since the use of fertility treatment has become more common.

Siamese twins (or conjoined twins)

  • Siamese twins are extremely rare.