In medicine, the measurement of effective prevention services is commonly expressed in terms of dosage or length of treatment. While in social policy it is important to know not only what to do to combat the causes but also how much intervention to provide, quantity is more difficult to define and resources or targets seem more apt perspectives. But the general question of the relationship between the amount and effects of an intervention applies in both contexts and is central to the planning and delivery of preventive services for children and families.

A recent report from the UK National Institute for Clinical Excellence summarises evidence about the amount of weight a new mother should lose before her next pregnancy. There is general agreement that all the baby weight should be shred before conceiving again, otherwise there could be complications in the future.

A common, and indeed seemingly sensible, view is that pregnant women need to “eat for two” and put on weight to boost their strength by consuming high-calorie foods, such as full-fat milk. But the scientific evidence urges caution.

The first warning is of the danger that high-energy foods will cause pregnant women to become obese, adding pounds that are unnecessary and difficult to shift. In fact, a woman’s energy only needs to increase in the last three months of pregnancy, and then only by 200 calories a day. This is the amount obtained by eating a single chocolate bar. All of the extra calories are superfluous and can only have bad effects.

The second message is that any extra weight that has been gained should be shed before falling pregnant again because a small amount - as low as two pounds (one kilogram) - increases the likelihood of problems arising in the new pregnancy. These include miscarriages, pre-eclampsia, diabetes and maternal death for the mother, and death, stillbirth, congenital abnormality, shoulder dystocia and child obesity for the infant. So serious are these risks that Lucilla Poston, director of maternal and foetal research at King’s College, London, summarises them as “almost every complication in the book”.

A third observation is the tendency for this problem of increased weight to continue with each pregnancy, so putting mothers and babies more at risk each time.

But it is not easy to lose weight especially at a stressful time and mothers are warned about the dangers of some media stories and commercial products that claim to produce unrealistic and rapid weight loss. This combination of inappropriate methods employed at a time of stress is just as harmful as retaining weight.

So the recommendation is for sensible weight control and better education about what is, or is not, likely to harm mothers and their unborn children. The achievement of a healthy Body Mass Index is an auspicious start and a balanced diet and moderate physical activity, such as cycling, while pregnant will not harm either of them.

In the UK, it is now estimated that between 15 per cent and 20 per cent of pregnant women are overweight or obese, with the numbers in the latter category doubling over the last 20 years. So the benefits of modest preventive action are manifest in terms of financial savings to the National Health Service as well as in healthier mothers and children.

Reference:
National Institute for Clinical Excellence, Weight Management Before, During and After Pregnancy, Public Health Guidance PH27, July 2010.
www.guidance.nice.org.uk