Just what are those pregnancy hormones doing to Shortland Street's sweetest nurse Morgan? First she kept jumping hunky Hunter, then she came on to best friend Gerald, and next thing you know she's snogging Trent, the biological father of the triplets she's carrying for him and wife Cindy.

"Dear God, that's three guys in the space of two weeks!" laughs Bonnie Soper of her sex-kitten character. "Morgan loves sex in the first place and she hasn't been getting any in a while, plus there's the hormones, too!"

Let's rewind to when big-hearted Morgan offered to be a surrogate for her childless friends Cindy and Trent. By impersonating Cindy, Morgan had Cindy's eggs implanted and fell pregnant, not with one baby but three. Shocked, the couple suggested she abort one foetus. A distressed Morgan realised she couldn't hand the babies over to a couple who'd suggest such a thing, and who'd not only broken up but lied about it.

With ever-loyal Gerald pledging emotional and financial support, Morgan decided to keep the babies who, legally, are hers. After Trent U-turns and agreed to this, he went after the package deal when he not only kissed Morgan but asked her to move in with him. Although she said no, Morgan still boomerangs between three wannabe boyfriends who all have their drawbacks: Trent means guilt, Hunter doesn't want babies, and Gerald's a sex-free zone.

After some time away to think, last week Morgan effectively renounced sex by proposing to "soulmate" Gerald. Delighted, he said yes, even though he knew Hunter (who saw the whole thing) was about to beg Morgan for another chance. Meanwhile, a desperate Cindy, who's turned up on staff, threatens to sue Morgan for sole custody of the children and take out a restraining order against her.

Don't take that deep breath yet. This week, Cindy tells colleagues about the surrogate situation. Disapproved of and even ostracised, Morgan is forced yet again to rethink. Will she change her mind about keeping the babies or about a sexless marriage? Will this end up in court? And which man will be standing next to her?

Although the dramatic palaver might seem unrealistic, the surrogacy storyline's not as far-fetched as you might think, according to longtime story editor Paul Hagan. "When we first discussed the storyline, people's anecdotes about real cases were more surprising than what we've made up." Having heard both dramatised and real-life stories from the point of view of the childless couple dealing with "the crazy surrogate", they decided to tell the story from the surrogate's point of view. "The legal advice we got was that the law would always support the pregnant woman who's viewed as the biological mother."

Well, that's the fallback position, as New Zealand has no laws covering surrogacy. Those considering it are at the mercy of the National Ethics Committee on Assisted Human Reproduction, but that's only if the prospective parents are doing it by the book, and most don't, says Sarah McLeod, who has done some extracurricular research since taking the role of Cindy.

"What's really interesting in New Zealand is that every year there's only something like one or two legal surrogacies [but] a huge amount go under the radar."

At Shortland Street's Christmas party, the script typist told McLeod that a friend of hers was surrogate for another friend. So McLeod and Soper, who get on famously in real life, met them and the baby for some crucial insights. In that case the surrogate didn't get too attached because she'd already had children, says Soper. But with the surrogate legally required to keep the baby for at least the first 10 days, it's not surprising that surrogates do feel attached.

"We found out it's actually quite common for surrogates to end up keeping the babies," says Soper.

Rubbing her fake belly during a break from filming, Soper's been "imagining these lives inside my tummy physically as well as mentally" to get into Morgan's headspace. Meanwhile, McLeod, 37, who's mum to Maisa, 9, and Lola, 6, found it easy to get into Cindy's head. "I just imagined my children being taken away from me."

Even when you consider the back story, Morgan's decision to keep the babies does seem rose-coloured-glasses at best and nuts at worst. Although slightly defensive, Soper understands how people could find Morgan's naivety annoying. "My sister keeps saying: `I'm sick of Morgan, she's does so many silly things'. Yes, she's impulsive, but I can relate to caring about someone to their detriment, possibly doing too much for them."

Aside from the issues of friends donating sperm or eggs, and where involvement ends, Hagan believes that assisted reproduction will spawn further moral, ethical and emotional issues.

"Reproductive technology is pioneering ways that two women can have a child that's biologically theirs without any male input, and a male couple may be able to have a child without involving a woman." And if that happens, odds are Shortland Street will be raising the issue.

* Shortland Street weeknights on TV2 at 7pm.