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Twin pregnancies: facts and fiction

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twin newborns crying


Many new mothers have stories to tell of unsolicited advice, intrusive questions and unwanted touching. But discovering that you are having twins or can expect a multiple birth can generate an even higher order of public discussion and comment. In the past decade, fertility treatments and the fact that women are having babies later has made multiple births more common. So how do you separate facts from fiction?

According to the Australian Bureau of Statistics there were the following multiple births in Australia:

  • In 2018, 1.4% (or 4,500) of confinements resulted in a multiple birth, remaining relatively consistent over the past decade.
  • 63 of these confinements were triplets or higher order.
  • Although there was an increase in the number of total confinements, there were 28 less multiple births in 2018 than in 2017.

The prospect of having twins probably raises many questions.

Different types of twins

One-third of all twins1 will be identical and two-thirds non-identical.

Identical twins

Identical (monozygotic) twins happen when a single egg (zygote) is fertilised. The egg then divides in two, creating identical twins who share the same genes. Identical twins are always the same sex, so if your twins are identical, you'll have two girls or two boys and they'll look very alike.

Non-identical twins

Non-identical (dizygotic) twins happen when two separate eggs are fertilised and then implant into the woman's womb (uterus). These non-identical twins are no more alike than any other two siblings. Non-identical twins are more common. The babies may be of the same sex or different sexes.

Are you carrying twins?

You might think you’re carrying more than one baby if:

  • you seem bigger than you should be for your dates
  • twins run in your family
  • you have had fertility treatment

It’s usually possible to find out if you're having twins through your ultrasound scan, which happens when you’re 10-14 weeks pregnant.

At the scan, you should be told whether the babies share a placenta (meaning they’re identical) or if they have two separate placentas (meaning they can be identical or not). If this isn’t clear from the first scan, you should be offered another one.

One-third of identical twins have separate placentas. This occurs when the fertilised egg splits before implanting in the uterus, up to four days after conception.

What causes twins?

Nobody knows what causes identical (monozygotic) twins. All pregnant women have approximately the same chance of having identical twins – about 1 in 250. Identical twins don’t run in families.

However, there are some factors that make having non-identical twins more likely:

  • non-identical twins are more common in some ethnic groups, with the highest rate among Nigerians and the lowest among Japanese
  • older mothers are more likely to have non-identical twins because they are more likely to release more than one egg during ovulation
  • non-identical twins run on the mother's side of the family, probably because of an inherited tendency to release more than one egg

In vitro fertilisation (IVF) can increase the chance of twins, as more than one embryo may be transferred.

How can I tell if my twins are identical?

The most accurate way to tell if twins are identical is through a DNA test. This can only be done after your babies are born.

The placenta could also provide clues. If your first ultrasound scan is done before 14 weeks, it should be possible to tell accurately what kind of placenta your twins have. Otherwise, the placenta can be examined after your babies are born. However, neither of these methods is foolproof.

Risks in twin pregnancies

While most multiple pregnancies are healthy and result in healthy babies, there are more risks to be aware of when you are pregnant with two or more babies. If you're pregnant with more than one baby, you're at higher risk from pregnancy complications, such as anaemia, pre-eclampsia and gestational diabetes.

Make sure you go to all your antenatal appointments, so any problems can be picked up early and treated if necessary. Twins and triplets have a higher risk of being born prematurely (before 37 weeks) and having a low birth weight of under 2.5kg (5.5lb). Triplets have a 94% chance of being born prematurely and of having a low birth weight.

Being premature increases the risk of problems after birth, such as breathing difficulties. Your obstetric team will work closely with you throughout your pregnancy and after your babies are born to help make sure you and your babies are safe and healthy.

Twin-twin transfusion syndrome

TTTS affects identical twins who share a placenta (monochorionic).

It’s caused by abnormal connecting blood vessels in the twins' placenta. This results in an imbalanced blood flow from one twin (known as the donor) to the other (recipient), leaving one baby with a greater blood volume than the other.

TTTS affects 10-15% of monochorionic twins and can have serious consequences. You'll need to discuss your individual case with your doctor, as what works in one TTTS pregnancy may not be appropriate in another.

Your birth choices with twins

It's a good idea to discuss your birth options with your midwife or consultant early on in your pregnancy.

You'll probably be advised to give birth in a hospital as there's a higher chance of complications with twins.

There may be more health professionals at a multiple birth – for example, there may be a midwife, an obstetrician and two paediatricians: one for each baby.

The process of labour is the same, but your babies will be closely monitored. To do this, an electronic monitor will usually be strapped to your bump.

A scalp clip may be fitted to the first baby once your waters have broken. This won't harm them or hurt them in any way.

You may be given a drip in case it is needed later – for example, to restart contractions after your first baby is born.

Triplets or more babies are almost always delivered by a planned caesarean section.

Can you have a natural birth with twins?

Lots of women think they have to have a caesarean section with twins. In fact, more than 40% of all twins are born vaginally and the process is similar to that of a single baby.

If you're planning a vaginal delivery, it's usually recommended that you have an epidural for pain relief.

If there are any problems, it's easier for your antenatal team to deliver your babies quickly if you've already had an epidural.

You're more likely to have a vaginal birth if the first twin is in a head-down position (cephalic).

However, there may be other medical reasons why this isn't possible. If you've had a caesarean section before, for example, it's not usually recommended that you have a vaginal birth with twins.

If you have a vaginal birth, you may need an assisted birth. This is where a suction cup (ventouse) or forceps are used to help deliver your babies.

Once the first baby is born, your midwife or doctor will check the position of the second baby by feeling your tummy and doing a vaginal examination. They may also use an ultrasound scan.

If the second baby is in a good position, it should be born soon after the first as the cervix is already fully dilated. If contractions stop after the first birth, you may be given hormones via a drip to restart them.

Caesarean section and twins

You may choose to have a planned caesarean, or your doctor may recommend a caesarean for medical reasons. 

If the first baby is lying feet, knees or buttocks first (breech position), or one twin is lying sideways (transverse position), you will have to have a caesarean section.

There are other conditions that make it more likely that you will have a caesarean section. For example, you may need one if you have a low-lying placenta (placenta praevia) or if your twins share a placenta (monochorionic).

If you have had a difficult delivery with a single baby before, you may be advised to have a caesarean section with twins.

As with any pregnancy, if you plan a vaginal birth, you may still end up having an emergency caesarean.

This could be because the babies become distressed, for example, or the cord falls into the birth canal ahead of the baby (prolapses).

In very rare cases, you may deliver one twin vaginally and then need a caesarean section to deliver the second twin. This happens in less than 5% of twin births.

Further links

Australian Multiple Birth Association 

Australian Breastfeeding Association

Twins Research Australia

Contains public sector information licensed under the Open Government Licence v3.0.