For most expectant mothers, an 8lb baby is more than enough to deal with.

So spare a thought for Sarah Chiad, who carried two of them.

Her daughter and son, Hannah and Thomas, had a combined weight of 17lb 8oz, almost double the average for twins.

Twintastic: Hannah, left, and Thomas, right, are the new siblings of Christopher, nine and five-year-old Rebekah

Double troube: Sara Chiad with her healthy babies, Hannah and Thomas, whose combined weight at birth was 18lbs

Hannah weighed 8lb 13oz and Thomas 8lb 11oz when they were born by caesarean section on January 11.

It means they are among the largest pairs of mixed-sex twins ever born in the UK.

Mrs Chiad had watched her waist grow to 57 inches during her pregnancy so she knew her babies would be big – just not that big.

But for the 38-year-old, all that matters is that the twins are healthy. She and her husband, Thomas, had endured three miscarriages in the past, including the loss of another set of twins.

She suffers from a rare blood-clotting disorder called Hughes syndrome or ‘sticky blood,’ which is one of the biggest causes of recurrent miscarriage. Clots form in the placenta, causing the pregnancy to fail.

Sibling love: Sarah, 38, had an inkling the twins she was expecting might be bigger than normal when her bump measured a whopping 57 inches

When Mrs Chiad became pregnant for the first time she was expecting twins, but that pregnancy ended in a heartbreaking miscarriage.

She was still oblivious to the blood problem when she later gave birth to 6lb 12oz Christopher, who is now nine. She said: ‘When he was delivered the placenta was full of clots and it was a miracle he survived.’ Mrs Chiad and her husband, a 41-year-old electronics engineer, tried for more children and two more miscarriages followed.

She was not given any tests in the UK, but when the family spent a period living in Austria she told a local doctor about her history and Hughes syndrome was ‘diagnosed straight away’.

The miscarriage risk is easily treated with blood-thinning drugs and as a result Rebekah was born, weighing 9lb 3oz. She is now five.

Mixed set: Sarah’s two older children said they were hoping for a brother and a sister, so they were happy with Hannah and Thomas

After slimming down to 15 stone from 21 stone, Mrs Chiad then decided to try for a third baby. She said: ‘We ended up with two instead of one. It was a shock but a nice surprise.’

She found out she was expecting twins at a seven-week scan, and was again given medication to prevent her blood clotting.

In 2007, a woman gave birth to the heaviest mixed-sex twins born in the UK, who weighed a combined 18lb 12oz

The pregnancy went without a hitch and the twins were born at 37 weeks.

‘When I saw them for the first time they were big but normal babies. I didn’t realise they were anything unusual,’ she said.

The average twin is around 5lb so staff at Chesterfield Royal Hospital were stunned when they weighed Hannah and Thomas.

The UK record for mixed-sex twins is a combined 18lb 12oz and Mrs Chiad believes she would have broken it had she gone to full term. ‘I knew they were going to be big but didn’t expect this,’ she said. ‘My health visitor said in 20 years she has never known such big twins.’

The babies, now five weeks old, are flourishing at home in Hasland, Derbyshire under the careful eye of their parents and older siblings.

Mrs Chiad said: ‘Rebekah and Christopher wanted one of each so they were delighted when they found out.’

Sarah said: ‘They are getting on very well and are good babies. They already look so different and have different personalities’

Achoo! According to Sarah, Thomas, right, is very chilled out while Hannah, left, is a bit more fussy