Conjoined twins Krista and Tatiana Hogan celebrated the first of many milestones this week.

The twin girls from Vernon, B.C., who are joined at the head, turned one-year-old on Thursday.

Brendan Hogan, the twins' father, told CTV British Columbia it has been a challenging year for the family, but one marked by progress and pride.

"I'm just happy it's their birthday and they've come this far and made it this long," Hogan said.

"It shouldn't be too hard for them to make it the rest of the way. They'll be fine."

Dressed in matching red dresses with white tights, the girls ate from a massive slab cake and played with rainbow-colored streamers while family and friends remarked on their progress.

"I'm very proud of my girls," the twins' mother, Felicia Simms, said ahead of the party. "I think the thing that I was most excited about was hearing (Tatiana) say her first word."

"They've broken through everything everyone thought the couldn't do and they're still here. It's awesome," Simms said.

The babies have undergone a slew of tests since their birth. In August, doctors working on the unique case deemed it too dangerous to separate the girls.

The decision came after doctors discovered the twins' brains were more intricately connected than they had predicted. They concluded their shared brain cells and blood vessels would have been severely damaged if they had undergone surgery.

Simms, 22, said one of the main worries about keeping the two together stems from Tatiana developing high blood pressure because her heart pumps most of her blood into her sister's body.

Both parents are hoping Tatiana, the smaller of the two, will catch up to her sister in the coming year. Neither baby is able to walk but Krista helps them flip over.

It is the first such case of twins conjoined at the head in British Columbia, although two previous sets of conjoined twins attached at the abdomen and one joined at the chest have been born in the province.

The odds of giving birth to conjoined twins attached at the head are one in two million.

With a report from CTV British Columbia's Michele Brunoro and files from The Canadian Press