"Eating for two is a myth, say researchers," reports The Guardian, saying that excessive weight gain in pregnancy is linked to the risk of diabetes in children.
Research among 905 mother and child pairs in Hong Kong found women who gained either less or more than the recommended weight during pregnancy had children who were more likely to show insulin resistance.
Insulin resistance is where cells in the body fail to respond to the hormone insulin, increasing an adult's risk of type 2 diabetes.
The children of these women were also more likely to be bigger, and have more body fat and higher blood pressure, compared with children born to women who gained pregnancy weight within the recommended amounts.
Since 2009, women in the US have been advised to gain weight during pregnancy according to their pre-pregnancy body mass index (BMI):
There have been calls for similar guidance in the UK so health professionals can appropriately advise expectant mothers.
But all the women in this study were of Chinese origin. Chinese women are likely to have different diets and weights from women in the UK.
This means it's unclear whether the results of this study would be the same in a group of UK women.
And insulin sensitivity doesn't mean someone will definitely get diabetes.
What we do know is that energy needs probably don't change in the first 6 months of pregnancy.
This was the conclusion of the National Institute for Health and Clinical Excellence (NICE), who issued new weight advice in 2010.
NICE advises that a woman's energy needs increase by around 200 calories a day only in the last 3 months of her pregnancy.
Read more advice about managing your weight if you're planning a pregnancy.
The researchers who carried out the study were from the Chinese University of Hong Kong and Tianjin Medical University in China.
The study was funded by the National Institute of Child Health and Human Development and the National Institute of Diabetes and Digestive and Kidney Diseases in the US, and the Research Grants Council of Hong Kong.
Media reports in the UK focused on calls from the Royal College of Midwives for the UK to adopt guidelines on recommended weight gain in pregnancy, and for pregnant women to be given advice about how much weight they should expect to gain.
But many of the headlines suggested there are confirmed plans to introduce these types of guidelines, which currently isn't the case.
Also, the Sun's headline ("Pregnant women may have to submit to regular weigh-ins") could be taken to mean that weight testing would be mandatory.
But as with all medical testing or interventions, women would have the option of choosing or declining these check-ups.
This prospective cohort study recorded data from women before pregnancy and birth, then examined the women's children at age 7.
Researchers wanted to see if the children's risk factors for diabetes were linked to their mother's pregnancy weight gain.
But this type of study can only find links between factors, it can't prove that one causes another.
This research used data from the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study conducted in Hong Kong.
The original study recruited women pregnant with a single baby, and asked their pre-pregnancy weight. Their pre-birth weight was then measured.
Women who had a pregnancy that went to full-term were invited to attend a follow-up with their child 7 years later.
The researchers were able to include 905 of the 1,667 women who took part in the original study.
At the follow-up visit, the children's weight, height, waist and hip circumference were measured. Researchers also checked their skinfold thickness (a measure of body fat) and blood pressure.
The children were given an oral glucose tolerance test, followed by blood tests to measure blood glucose and insulin levels during the next 2 hours.
These figures were used to measure insulin sensitivity using 2 tests: the homeostatic model assessment of insulin resistance (HOMA-IR) and the insulin sensitivity index (ISI).
Researchers took account of a number of potential confounding factors, including:
Comparing women's pregnancy weight gain against the 2009 US Institute of Medicine guidance:
Compared with the children of women who gained the recommended amounts of weight, children of women who gained more weight than recommended:
Children of women who gained less weight than recommended also had a slightly higher diastolic blood pressure and insulin sensitivity. But this may not have been a clinically significant difference.
The researchers said their results confirmed the results of previous studies showing that weight gain during pregnancy could affect children's later metabolic health.
They said: "One of the most important findings from this study was that, independently of maternal pre-pregnancy obesity and glucose level during pregnancy, maternal GWG [gestational weight gain] had a U-shaped relationship, with increased odds of childhood insulin resistance and hypertension."
They went on to say pregnancy may represent a "potential window of opportunity" for women to improve their diet and exercise, which would benefit the health of the next generation.
This study adds to evidence that keeping healthy during pregnancy, with a good diet and plenty of exercise, can give the baby a head start when it comes to its own health.
There's a pervasive myth that women need to "eat for 2" while pregnant, but that's not true.
Most women don't need to increase how much they eat or take in many extra calories (though the types of food they eat may need to alter).
This study has some limitations to be aware of. Because it's an observational study, we can't be sure that the children's size, body fat and blood pressure were a direct result of women's weight gain in pregnancy, as other factors may have affected the results.
Young children in particular are influenced both by their parents' genes and the foods the family regularly eats, the amount of exercise the mother takes, and the general environment they live in.
It's possible that women who put on more weight in pregnancy have a generally less healthy diet and do less exercise, and that this could have partly accounted for the results.
Also, the study was carried out entirely in a Chinese population. We don't know if the results would be the same in a UK population.
Risk factors for diabetes differ in some Asian populations, and average diet and body size is also likely to differ between the UK and China.
In the study, the women's weight before pregnancy was reported by the women themselves, rather than measured by researchers, which means it may have been less accurate.
Also, many of the women in the original study did not take part in the follow-up. We don't know if the results would have been the same if all the women had been included.
But the general message of the study is likely to hold true. Diet and nutrition are important in pregnancy, and too much weight gain could have implications for the baby.