Young US couple who already had three sons were told that they are expecting TRIPLETS (Details, pics)

A couple who first welcomed one child, and then twins, are now expecting triplets.

Nia and Robert Tolbert from Waldorf, Maryland, were in shock to discover they were expecting three girls during a routine prenatal doctor's visit back in August. The nurse asked Nia if twins ran in her family, leading the 28-year-old mom to believe she was having twins again.

She got up to use the bathroom and when she returned, the nurse told her that she was in fact carrying three babies.'

She said: "There's three. Baby A. Baby B. Baby C,"' Nia told WUSA9.

Dr Rami Tabbarah, an OBGYN at Inova Women's Hospital said that several factors play a role in producing multiples - a woman's height, heredity, ethnicity and age.

'I just never thought I would see that letter - Baby C. I said: "Can you check and make sure it's not four?"'Both Nia and Rob have multiples in their families, and Nia also learned she hyper ovulates, which means more than one egg is released at the same time.

'Hyperovulation is very rare,' Dr Tabbarah said. 'Eight people out of 1,000 [in the US] might be hyper ovulators and those will be the people that get the twins.'

Nia decided to share the big news with her husband of three years, Robert, 31 with a gift bag containing a handwritten note.

Robert told ABC News that at first he thought the gift bag contained a Fitbit, since he'd been hinting at getting one for weeks.

On a handwritten card, Nia had written: 'Please accept this gift from me and God.

'Robert opened the bag and found a sonogram and three onesies numbered one, two, and three.

'Oh I passed out. I hit the bed. I blinked twice, when I woke up I saw that some time had elapsed on the clock,' he joked.

Despite the initial confusion and panic, the parents say they're looking forward to their growing family. The triplets are due in March.'

We're already planning for our new household. It's going to be equally balanced now - with three little girls and three little boys,' Nia said.

'But we're not too concerned. I know we're not going to sleep for a couple years, our grocery bill is going to go up, and our house is not going to be quiet and that's OK.'