Since the 1980's the incidence of twins and multiples has increased dramatically with the most recent figures suggesting than approximately 150 out of every 10,000 births are multiples with a third of these being identical and two thirds being fraternal.What's the difference between identical and fraternal twins?Genetically, fraternal (or dizygotic) twins are only as similar as siblings.

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However, others sail through the early weeks without any trouble at all so this is not a definite indicator by any means.

Greater weight gain during the first trimester can also be a sign but again this varies from woman to woman and may simply be due to a miscalculation of due dates rather than a multiple pregnancy.

The only sure way to find out if you're expecting twins or more is by having an ultrasound, so if you're not there yet you could get a big surprise when you have your first scan! If you're expecting more than one baby it's natural to want to find out whether they'll be identical or not.

On the other hand, identical (or monozygotic) twins share the same genetic makeup as they come from a single egg that split during the first few days of the pregnancies development.

What affects the chances of having twins and multiples?

Fertility treatment - The increased advancement and availability of fertility treatments have played an active role in making twin and multiple births more common.

This is because many of these treatments either stimulate the ovaries to produce eggs (making it more likely that more than one egg is matured and released during each menstrual cycle) or, as with IVF, two or three eggs are implanted into the womb, again allowing the potential for more babies to develop at the same time.

Age - Age also influences the likelihood of multiple births with 'older Mums' being significantly more likely to conceive twins than those in their twenties.

This is thought to be because women's bodies produce increasing amounts of the hormones that stimulate ovulation as they grow older, making it more likely that more than one egg will be released per cycle.

Heredity - Fraternal twins are said to run in families, being passed down genetically on the mother's side.

This could potentially be down to a gene for hyper-ovulation that's passed through the generations making it more likely that a woman will release more than one egg during ovulation. Size - Research has suggested that maternal height and weight plays a role in the likelihood of multiple births with taller women and those with a BMI of 30 or more being more likely to have more than one baby. As nurturing a multiple pregnancy places more strain on your body, many women report experiencing stronger pregnancy symptoms earlier on, with many having more extreme fatigue and morning sickness.