When Meredith Wooley decided to lose weight for her wedding day, little did she realise that something was ticking away inside her - the heartbeat of a baby.

For 36 weeks, the 26-year-old Christchurch woman was unaware she was pregnant, until her fingers and ankles began to swell. She took a home pregnancy test, which indicated she was expecting, confirmed soon after by a scan. Three-and-a-half weeks later, Wooley and partner Joe Mildenhall were proud parents of son Harrison.

Wooley said she hadn't noticed any stretch marks or kicks. She had not thought her stomach looked any different. But she had gained some weight, half a kilo, despite trying to shed some with a regime of healthier foods and Highland dance classes.

In hindsight, she said the only obvious oddity she had noticed was developing an aversion to ham sandwiches. She did not experience morning sickness and her menstrual cycle had continued as normal.

Said Mildenhall: "We were shocked. But once we got our heads around it, it was very cool. It was just a case of getting everything ready." Harrison, weighing 3.3kg, was born at 6.55am on August 2.

"Normally, you get nine months to prepare for it, but it was awesome. It took 10 minutes to click that he was mine," said Wooley.

Now, 10 weeks into parenthood, the two say Harrison was the best surprise they could have hoped for. And his arrival has not altered their wedding plans. When they found out Harrison was on his way, they had already had their wedding invitations printed, so they will marry as planned this month.

Wooley said she loved being a mother. "He is a really good baby. He is really cruisy, smiley and cheeky." He even slept through the September 4 earthquake, she said. The couple said Harrison's birth, at Christchurch Women's Hospital, had been an "amazing" experience.

"It was surreal holding him and saying, 'A month ago we were planning a honeymoon in Hawaii and now we are here'," said Mildenhall, who is planning on being a stay-at-home dad for a year after Wooley's maternity leave ends in six months.