Many women fail to get proper advice on weight management during and after pregnancy, a UK-wide survey suggests.
Some 63% said their midwife had not explained obesity issues such as body mass index during their first antenatal appointment.
The poll of 6,226 women also found that six out of 10 felt pressurised by celebrity culture to lose weight quickly after giving birth.
They were surveyed by the Royal College of Midwives and website Netmums.
Obese, pregnant women run a greater risk of developing conditions such as pre-eclampsia and gestational diabetes.
They are also more likely to experience miscarriages, difficult deliveries, pre-term births and caesarean sections.
The survey found almost half the women who responded were worried about their weight during pregnancy.
But many appeared to be confused about what their correct weight should be, and significant numbers worried unnecessarily that their weight might cause problems giving birth.
As well as missing out on obesity advice during pregnancy, nine out of 10 said that after giving birth they had had no opportunity to discuss their concerns with their midwife.
Overall, 84% said the general advice they received from midwives on weight management was not good.
Nearly three-quarters (73%) of those who responded said the NHS should provide midwife-led antenatal classes specifically to address healthy eating and weight management.
The survey also suggested that lack of care had damaged many mothers' self-esteem. When asked how they felt about their body while pregnant, comments ranged from "disgusting" to "fat, ugly and big".
Sally Russell, a co-founder of Netmums.com, said: "The results from this survey are a wake-up call to midwives to support women better throughout their pregnancy and inform them of their options."
Cathy Warwick, RCM general secretary, said good advice on weight management was vital, both to ensure that women kept as healthy as possible during pregnancy, and to avoid the risks being exaggerated.
But she said midwives did not seem to have enough time to discuss concerns with mothers-to-be.
She called on NHS Trusts to make sure resources were made available to ensure women got the advice and support they needed.
About half of women of childbearing age are either overweight or obese, with levels rising.
The health watchdog, the National Institute for Health and Clinical Excellence put out guidance in July encouraging women in England to attain a healthy weight before they get pregnant.
A Department of Health spokesman said: "We know it's crucial that mothers get the support they need before, during and after birth and we are working with the Royal College of Midwives, the NHS and others to make this happen.
"Obesity can have serious consequences for mothers and babies. Women need information, education and support at every opportunity.
"Health visitors have a key role in making sure that all mothers and babies get advice about what to eat, exercise and lifestyle. We are committed to recruiting an extra 4,200 health visitors who will be able to give professional support to women and we are currently exploring with the profession how best to achieve this."
In 2009 there were 26,678 full-time equivalent midwives in the UK.
BBC News website readers have been sending us their thoughts on this story. Here is a selection of their comments.
Isn't this a case of how to handle the horse once it's bolted? I was obese and got pregnant. My midwife did mention my BMI and explained that it put me at higher risk, so I would therefore need more scans throughout my term. She didn't bang on about my weight presumably because I couldn't diet by that stage. Is it right that a midwife starts to point fingers and say that mothers are the cause of so many potential problems during their first appointment? In this time, they are supposed to be developing a rapport with the patient so they can also find out other things such as cases of domestic violence, or history of depression. Kathryn, Chester, Cheshire
I am currently 37 weeks pregnant and have received no specific advice from my midwife about weight gain/post-pregnancy weight loss. However, there is plenty of advice given in publications produced and provided by the NHS as part of the process. I have the opportunity to ask questions of my midwife, but haven't felt the need. There are lots of resources accessible freely on the internet and in libraries on healthy diets generally, but specifically in pregnancy. Clair, Watford
I have had no help with weight, since becoming pregnant for the second time. After having my first child I had no help from either my midwife or GP about my weight, I noticed they are too busy trying to promote breastfeeding. Maybe they are just way too busy to be able to sit and talk to you about anything because of the amount of people they have to see. Tanya, Birmingham
I'm 13 weeks pregnant with twins. I have found most of the information I need from surfing the web. Most people have internet access now, so with the ever over-stretched NHS, this is a godsend. Helen L, Weymouth, Dorset
Shouldn't healthy eating be your first choice whether you are pregnant or not? Does everyone in this country need to be spoon fed the obvious? Simon Stringer, Barnstaple, Devon
I am a first-time mum-to-be at 37 weeks pregnant. I'm also included in the high-risk category of being obese during pregnancy, with a BMI of over 30. From your article, I appear to be one of the lucky ones and was able to discuss my weight issues with my midwife, so much so that I was referred to an NHS dietician. As a result I've managed to avoid putting on less than half the weight that the average pregnant woman can put on. C Hunter, Isle of Skye
I spent the first six months of my pregnancy in Spain and the final three in the UK, and gave birth here. I have always had a healthy BMI. In Spain my weight was carefully monitored. At one point I was urged to take extreme care, as I had put on a couple of kilos "too quickly". I spent the next month or so eating exceptionally healthily with no sugary or salty snacks at all. Pips, Norwich, Norfolk
I'm a midwife and the first appointment that we have with a pregnant lady is one hour long. In that hour, we have to gain information about their obstetric history, their medical history, their social history, explain scans and blood tests, take some blood if the lady consents, explain the plan of care, refer the lady for her ongoing care and fill out various other paperwork as well as arranging the next appointment. While we do take their BMI index, it often isn't the right time for some women to have their obesity pointed out by a midwife, especially if they have an unexpected pregnancy. Yes, there are opportunities to go through this information at a later time, but at the booking-in appointment it isn't always possible. Vicky, Peterborough
I was asked about how much I weighed at my booking appointment, but have not actually been weighed once throughout my pregnancy or been asked for my weight. I am now in my third trimester. Anke Twigg-Flesner, Gloucestershire
It makes me angry that midwives are being blamed for the failings of women. Why is it a midwives responsibility to give advice about weight loss? If you are overweight before you get pregnant and have done nothing about it, when you become pregnant you can transfer the responsibility onto yet another health professional. Having had weight issues myself and lost a significant amount of weight, it is each individual's responsibility to control what you are putting in your mouth. Alison Martin, Manchester
I am a dietician and also currently pregnant. I feel that midwives are not best placed to provide weight-loss advise and this should be a problem that is dealt with prior to women becoming pregnant. Dieticians are the nutrition experts and should routinely meet newly pregnant women to warn them of the risks of weight gain during pregnancy. Sasha Watkins, London
I am not at all surprised by this. The midwives at the hospital were fantastic but the ones in the community were over-stretched and gave next to no support during my pregnancy. I asked about the size of my bump due to comments. I am a size 8-10 and they said my bump was normal. This was incorrect as I had a 10lb 2oz baby by emergency caesarean section. With the current cuts no more money will be given to improve this though. Sarah, Stratford Upon Avon