Chalk, toothpaste, ice cream with chips; Lisa Salmon asks why stomach-churning combinations are craved when a baby's on the way.

If you've never been pregnant, it's probably easy to dismiss weird and wonderful pregnancy cravings as an exaggeration or myth.

But most experts - and of course women who have been pregnant - say otherwise.

A new survey, by C&G Baby Club Community, revealed expectant mums hankering for everything from chocolate (30%), sour pickles (29%), and salty crisps (28%); to the slightly less standard soap (11%), chalk (6%) and toothpaste (5%), as well as rubber, paint and rocks. One woman even confessed to a desire for tree bark, and another was hungry for the smell of tennis balls.

A quarter (27%) of respondents liked to mix things up too, confessing to a liking for bizarre mixtures of sweet and savoury foods, including sausages and jam, Mars bars and bacon, and Yorkshire pudding with chocolate spread. If that wasn't enough, there was also ice cream and chips, prawn cocktail crisps and strawberry yoghurt, cheese and onion crisps with Nutella, chicken and ice cream, and sweet and sour curry with salad cream.

It might not be a menu to tempt everyone, but consultant obstetrician Dr Virginia Beckett, a spokesperson for the Royal College of Obstetricians and Gynaecologists, is unfazed.

"It's common for women to notice that their sense of taste changes in pregnancy, so foods they previously enjoyed may be less palatable. Also, foods they never really cared for will be irresistible."

These urges commonly occur three to five times a day for more than a third of mums (36%), according to the survey, and 34% of them turn to an online delivery service to stock up on their unusual urges. Nearly half (49%) of hungry mums-to-be would also be prepared to travel up to 10 miles to get what they crave - and a desperate 9% would travel even further.

Money is clearly no obstacle either; 15% confessing they'd splash over £50 to satisfy their craving, worrying they'd end up feeling anxious (23%), upset (21%), angry (20%) and frustrated (18%) if they didn't.

All these figures add up to prove that, whatever some people might say, pregnancy cravings are a firm fact; but what is less certain, is why.

Extensive research over the last 40 years has failed to pin down their cause. Dr Beckett, author of the pregnancy guide My Pregnancy (Dorling Kindersley, 2011), suggests one reason for this is because the need for hydration increases in pregnancy, leading to cravings for fruit and cold foods.

Midwife Jane Munro, a professional advisor for the Royal College of Midwives, adds: "There have been suggestions that [cravings] are linked to hormonal change, but that's not backed up by the evidence.

"We don't know the reasons for the cravings, they could just be an extension of what you normally fancy. Often what you crave in pregnancy is the same as things you craved when you weren't pregnant."

But she warns that women need to ensure that if they crave unhealthy food, they don't eat too much of it, as a healthy diet is important during pregnancy. And if a pregnant woman is craving non-food items, she should always talk to her midwife to make sure consuming them isn't harmful to her or the baby.

Dr Beckett agrees: "Occasionally, cravings are for non-food items which could cause harm. Eating soil, for example, could lead to parasitic infections, and crunching ice can damage the teeth."

She says that in severe cases, mineral - particularly iron - deficiency may be suspected as a cause of cravings, but adds that "psychiatric conditions such as obsessive compulsive disorder (OCD) may also present bizarre cravings, requiring additional psychological support."

In most cases though, thankfully, pregnancy cravings are no more than a fleeting fancy, and Munro stresses that women generally have no need for any worry.

"If you have any concerns, talk to your midwife - if you think you're overeating sugary foods for example. But although most women do experience cravings during pregnancy, they usually go away."

Ask the expert

Q: "I'm one of those women who thought I could 'have it all' after having kids - but I'm just exhausted. How can you have a satisfying life when you don't have enough time to do anything well?"

A: Life coach Erica Sosna, author of Your Life Plan (Capstone, £10.99, published March 7), says: "I think this 'you can have it all' concept is risky. Firstly, it says that where you are and what you're doing isn't good enough and that if you can expand, grow, and put more on your plate then you should do.

"I disagree. I think if modern life choices have afforded us anything, it's the right to know when is enough, to find out what really matters to us, and to choose accordingly.

"So how can you address the need to be a great parent and a career superstar?

"Start by being grateful for what already works - do you have enough to eat? Do you have people around you who support and love you? A healthy child? Great - celebrate those things. Then begin to look at how and when you know you've done enough.

"Define what successful 'enough' looks like. Good enough parent? Kind enough partner? Is there a time you can see when you will ever reach your end goal?

Maybe the process of getting there is ongoing - so if you have a lifetime to get it right, you can relax.

"Know what matters to you. Celebrities may think it's fine to leave their kiddies with the nanny, you may not. At the end of the day, your choices about time and priorities come down to your values. What do you most value in life? Freedom? Adventure? Stability?

"Once you know what matters most to you, the right choices to make that line up will become clear."

Maternity style

Mamas & Papas SS14 Range

A maternity range including tops, dresses and jeans, featuring easy shapes re-worked with vibrant colours. Available from mamasandpapas.com, priced from £24.

Bravado Body Silk Seamless Maternity & Nursing Bra

A soft, seamless maternity bra made from a stretch fabric which grows with mum during pregnancy, and accommodates fluctuations in size when breastfeeding. Converts to a regular bra when no longer breastfeeding. Available from bravadodesigns.com, £30.

Amoralia Daddy PJ Short Set

Cute soft fabric maternity pyjamas made in a more masculine shape so they can be worn during and after pregnancy, with low-cut shorts that fit under the bump, and handy pockets for new-mum necessities like muslins. Available from www.amoralia.com and Kiddicare stores, £59.