If you're told your baby is underweight, it could be the growth charts that are wrong

When a baby is born, everyone wants to know its weight. But my baby's size, or lack of it, was an issue for six months. She wasn't putting on enough weight, health visitors said. Other babies' growth charts climbed steadily, but not Alice's. In some weeks she put on just a few ounces, in others her weight leapt up.

For Alice and me, this hardly seemed a problem. I enjoyed breastfeeding and was blissfully happy. But the weighing clinic and those fortnightly interrogations did grind me down. Was I eating enough? Was baby latched on? A health visitor suggested I give formula milk: "You want to see she's thriving," she said. Alice was tested for a urine infection (nothing). Then we had an emergency doctor's appointment (she was fine). But the nagging continued.

It's difficult to describe how undermining this is. Babies don't come with instruction manuals. From the moment they love-bomb your life, all crumpled faces and incomprehensible cries, you have an instinct to protect them. And to be told that you are failing as a mother to give them adequate food is demoralising and distressing. By week 18, I was so fed up that I decided to top her up with formula milk instead.

I didn't realise then that I was following a well-worn path for breast-feeding women. I started to hear whispers; the charts were "flawed", based on formula-fed babies, who tend to put on more weight than breast-fed ones (and not good weight). At first, I treated the rumours with caution, but the rumblings grew louder. One mother confessed to not taking her second baby to be weighed at all, she'd had such worry with her first.

So I looked into it, and guess what? Formula-fed babies are heavier; after the early weeks, they have higher intakes of energy compared to breast-fed babies' lower body temperature and lower metabolic rate (on average). And the chart standards Alice was failing to meet? Based on the growth of mainly formula-fed infants.

In 2005, the World Health Organisation said it would publish new growth charts, based on the optimum growth standards of breast-fed babies. "Formula-fed infants and breast-fed infants grow differently," said Dr Mercedes de Onis of the WHO. "The problem is that by these [current UK] charts, breast-fed babies seem to be growing poorly from as early as two to three months. But the problem is not that the baby is not growing well, it is that the standards do not reflect the growth of breast-fed infants." And the bombshell; the WHO charts showed that British babies were significantly heavier than they should be.

So where are the WHO charts? Professor Charlotte Wright of the Royal College of Paediatrics and Child Health says they have just gone to public consultation. "The important thing is that they are introduced in a way that works and doesn't cause confusion. People don't realise how complicated it is."

"Ridiculous," counters Tam Fry of the Child Growth Foundation. "We've known the charts were being produced since 1993, and the dramatic way they would affect the first year of life. The work had been done."