Women with acute morning sickness, such as that suffered by Kate Middleton, must be given drugs and counselling to stop them wanting a termination, UK experts said as they issued new guidelines.
Hyperemesis gravidarumeach, can lead to constant vomiting, weight loss, dehydration and depression.
To explain more about morning sickness, here are the top 10 myths busted:
Myth: All morning sickness is the same
Caitlin Dean, vice chair trustee of Pregnancy Sickness Support in the UK stresses this is not the case.
"Pregnancy sickness is on a scale. You have got your normal morning sickness which women expect. But then you have women with more severe sickness which isn't normal."
This is hyperemesis gravidarum (HG) which can result in constant vomiting, to the point where the woman cannot ingest even a glass of water without being sick, crippling weakness and excessive dehydration.
Myth: HG isn't that big a deal
"If it's untreated, it can lead to very severe complications," stresses Dean. In some cases, women resort to abortion, but it can also lead to other issues.
"Before we had IV tubes and so on, it used to be the leading cause of death. Even now women can still, very rarely, die from complications such as deep vein thrombosis, dehydration and so on."
It can also cause psychological illnesses such as depression and post traumatic stress disorder.
Myth: Morning sickness is always in the morning
"One of the biggest myths is it isn't always in the morning," says Clare Byam-Cook, former midwife, author and breastfeeding expert.
"A lot of people think it happens first thing and then you're fine for the rest of the day but actually it can happen any time."
Myth: It only lasts three months
Typically, morning sickness does only last for three months. But if you suffer from HG, it can last throughout the woman's entire pregnancy.
She may notice an improvement at 20 weeks, but Dean says that she should get urgent medical care.
Myth: The baby will suffer
"The baby won't suffer," says Byam-Cook. "A lot of people think if they're being sick because the food they're eating is coming out, the baby will end up lacking nutrients. The worse that happens is you lose weight but the baby will be absolutely fine."
However, if the woman is suffering from HG, it could potentially harm the baby unless she receives professional care.
Myth: HG is your fault
"HG is an extreme morning sickness and it's just bad luck," explains Byam-Cook. "It's just one of those things that happens."
Dean says that people may think "these women are weaker, and that it's a psychological disorder." But she stresses: "It's just untrue. We know that it's not to do with being unhappy or anything."
The Duchess of Cambridge was hospitalised with hyperemesis gravidarum when pregnant with Prince George
Myth: You can't take any medication
Almost 60 years ago, women were given drugs, including thalidomide. But that resulted in a huge scandal where babies were born disabled - and, as a result, many are wary of turning to drugs today.
"Ever since then people have been far more cautious and said you can't risk taking any medication at all that might damage the baby," says Byam-Cook. "From that point of view, people just say 'tough' to the mother, 'you'll recover'."
But women can take antiemetics (a drug that is effective against vomiting and nausea), according to Dean. And if they are suffering from HG, could be given Ondanestron - a power anti-nausea drug that is recommended in the National Institute for Health and Care Excellence guidelines for HG.
Myth: You don't need to take time off work
With HG, a woman will need to take time off work. But even regular morning sickness can be problematic.
"It's unpleasant but you won't die of it," says Byam-Cook. " But it depends on your job. If you're a heart surgeon, you don't want to rush out to puke up. In some jobs when you can't rush to the loo, it's actually quite frightening, or if you're commuting in rush hour."
If possible, women should talk through their options with an employer.
Myth: All women hate morning sickness
Actually, Dean says: "Many women look forward to it. They see it as a right of passage and life experience to clock up and a sign of a healthy pregnancy."
Myth: It shows you're having a boy
"People often think it's to do with the sex of the baby," explains Byam-Cook. "The first time you get morning sickness and let's say you have a boy, if you get it the second time round, they'll say it's because of the change of sex. That's a really old wives' tale."