Krystal Sinclair, who measures just 142 centimetres in height, was almost as round as she was tall when she gave birth to triplets by emergency caesarean at John Hunter Hospital on Sunday.

The usually petite Ms Sinclair said doctors were concerned about the fate of her pregnancy especially after learning the father, Lucas, was 190 centimetres tall.

However Aleah Rose, Tahlia May and James Lucas were born healthy after 28 weeks of pregnancy and together weighed more than 3.5 kilograms.

In another stroke of fortune the two female babies are identical twins.

The chance of having triplets is one in 8000 but the chance of having a set of identical twins in the birth is one in 40,000.

It was the first pregnancy for the couple, who conceived naturally.

They now have a house full of items in sets of three, six and nine thanks to supportive friends and family.

Ms Sinclair, 21, said it was likely to be her last pregnancy.

"When I found out I was shocked. There is no history of any of this in my family," she said. "It took me about two months to come to grips with it."