For most mothers, a 6lb baby is enough to carry.

But Kate Tipton carried three.

Last month the Tennessee-based mother gave birth to the second heaviest set of triplets in world history.

Jack, Stella and Luke Tipton weighed 7lbs 4oz, 6lbs 3oz, and 5lbs 9oz respectively.

Together, that is 19.6lbs.

Looking swell! Jack, Stella and Luke Tipton weighed 7lbs 4oz, 6lbs 3oz, and 5lbs 9oz

In disbelief: Kate and Caleb Tipton, who now have five children, were astonished to welcome the second heaviest set of triplets in world history

It came as a shock - not least because her doctor had spent weeks warning that the babies would almost certainly be cripplingly underweight - and may not make it.

This week, Kate and her husband Caleb consulted the Guinness World Record book - and discovered they missed the mark by just 2.4 pounds.

The heaviest triplets on record were born in Colorado in 2003, weighing a collective 22 pounds. There may have been other heavier births not recorded by Guinness.

Looking back, Kate says there were signs that she was carrying quite a lot - nothing like with their daughters Sophia, now aged nine, and Aubrey, now aged eight.

'I would stand up and you could literally hear my hips crack. They would make this noise. The sound of so much pressure on top and so much weight. It was difficult,' Kate told WBIR.

'I would have cried every day if it was my body going through that,' Caleb added.

A journey: Kate and Caleb recall Kate's hips cracking under the weight of the big babies

Nonetheless, going into labor, she never thought they would weigh this much.

She first went into labor at 21 weeks and required emergency surgery to stop the labor and continue pregnancy.

At 34 weeks - technically six weeks premature - she went into labor again, and this time it could not be stopped.

Once again, the midwives and doctors explained that there was a strong chance the babies would be tiny, weak, and struggling for life.

When they finally arrived, everyone was taken aback.

'We were shocked,' Kate told ABC News today.

'They weighed Jack twice. He was first. They thought, 'That's not right. He can't weigh 7 pounds, 4 ounces as a triplet.'

'There was so much noise and excitement and disbelief.'

Before they were born, doctors warned the babies would be underweight and premature

Even the family's doctor was surprised, saying he had never seen this in 25 years of practice.

'I look back now and I said, 'Wow, what if I had been pregnant another week?',' Kate said to Today.

'But, I did not want to be pregnant any longer. They were the biggest in the history of UT Medical Center.'

Now, the family faces new challenges: Jack, Stella and Luke go through 115 fluid ounces of milk a day, and 30 diapers, to the tune of $500.

'The days are busy,' Kate admits.