Happy times ... There's a huge variation in when couples decided to announce their news.

Happy times ... There's a huge variation in when couples decided to announce their news.

How long should a couple wait until revealing they're pregnant?

It's a decision the Duke and Duchess of Cambridge had largely taken away from them last week, when Kate was hospitalised with hyperemesis gravidarum.

Hiding a pregnancy until the conventional 12-week mark would be understandably difficult between sessions hooked up to an intravenous drip while struggling to hold down even a glass of water while the hysterical media looks on.

Big announcment ... the Duke and Duchess of Cambridge's official website delivers the baby news.

Big announcement ... the Duke and Duchess of Cambridge's official website delivered the baby news. Photo: Getty Images

But according to The Royal Australian and New Zealand College of Obstetricians and Gynaecologists spokesman Gino Pecoraro, there is "nothing magic" about the three-month mark in a pregnancy, and there are no guidelines dictating an ideal time for announcing one.

"Around the 11-to-13 week mark, women undergo a nuchal translucency screen to estimate the risk of the baby having Down syndrome," he said.

"That's the main reason some women wait until after then. But in terms of miscarriage, that is actually most likely around the seventh week."

Dr Pecoraro said while the nuchal translucency screen, introduced about a decade ago, may have contributed to more women waiting until the 12-week mark to announce a pregnancy, he saw a huge variation in his own patients and when they decided to announce their news.

"It is an intensely personal thing for couples," he said.

"The trade-off of telling people early is that if something bad does happen, family and friends know and you will have their love and support, though having everyone know may be off-putting to other couples in the same situation.

"There is no right or wrong time."

In healthy women, about one-quarter of all pregnancies ended in miscarriage, he said.

"That's not as awful a statistic as it sounds," Dr Pecoraro said.

"Miscarriage can happen really, really early in a pregnancy before women even know they are pregnant. It is nature's way of keeping a track on things and if something is significantly wrong that can't be compatible with life.

"But women who have had multiple miscarriages may be understandably reluctant to announce a subsequent pregnancy until later on."

Hyperemesis gravidarum: the basics
Hyperemesis gravidarum was an uncomfortable condition, Dr Pecoraro said, that could lead to constant vomiting and sickness at all times of day.

So is it possible for most women with the condition to have an otherwise healthy pregnancy and child?

"Oh god, yes," Dr Pecoraro said.

"All it means is significant vomiting to the point of putting some people in hospital for a drip so they can be re-hydrated, so while that is very unpleasant, hyperemesis gravidarum by itself doesn't mean there is a problem with the baby."

In many cases the condition was likely related to the level of hormones and the placenta, he said.

"So anything like twins or triplets will of course also mean an increase in the amount of hormones and particularly high levels of estrogen can make women feel nauseated.

"For some women who have had miscarriages, experiencing those dramatic symptoms can actually be a relief because it makes them feel like their baby is well and active."

Hyperemesis gravidarum by the numbers

  • 0.3-3 per cent: number of pregnant women experience HG
  • 5 per cent: the minimum body-weight loss of women with HG
  • 16 weeks: the gestation period when HG usually settles down in most women (but a small minority can experience severe symptoms up until delivery)
  • 15.2 per cent: the number of sufferers surveyed in a Hyperemesis Education and Research Foundation survey said they had had at least one termination due to HG
  • 95 per cent: the recurrence rate for HG