Hi, I'm very happily pregnant and I am trying to do the best by my new baby. The thing is, I've been trying to eat healthily and do light exercise and I'm now worried I'm not putting on enough weight. I weigh myself every week and this week I've actually lost a pound, am I harming my baby? I'm 16 weeks and I've only put on 6lbs.

Try not to worry; your weight can fluctuate by a few pounds depending on the time of day, your level of hydration and even the clothes you are wearing. If you have been eating well, loosing one pound shouldn't indicate that there is cause for concern.

Weight gain should start during the second and third trimesters of pregnancy and can be very different from woman to woman. The optimal weight gain during pregnancy depends on your pre-pregnancy weight. For those women considered underweight (with a body mass index (BMI) lower than 20) a weight gain of 0.5kg or 1lb per week from week 12 onwards is an approximate target. For normal weight women (BMI between 20 to 25) their target is a weekly weight gain of 0.4kg or ¾lb per week from week 12 onwards and for overweight women (BMI over 25) 0.3kg or 1/2 lb per week is recommended.

It may be easier to consider the above in terms of total weight gain as it is common for weight to fluctuate and not always follow an exact pattern. The 1, 2, 3 rule recommends that overweight women gain around 1 stone during pregnancy, normal weight women gain 2 stone and underweight women gain 3 stone.

To put on an appropriate amount of weight, try to eat three meals a day and have healthy snacks such as fruit and low fat yogurt in-between meals, eat plenty of fruit, salad and vegetables to help you to feel full, and drink water regularly throughout the day. Remember that the quality of your diet is as important as the quantity and you only need 200 extra calories for the last three months of pregnancy.

The foods to eliminate from the diet are those that are high in fat and/or sugar, e.g. cakes, biscuits, processed foods like pasties, sugary fizzy drinks and crisps. These contribute very few vitamins or minerals to the diet, just lots of energy. These should be replaced with starchy carbohydrates, and moderate amounts of dairy and meat or fish (or meat/fish alternatives). Eating a balanced diet will ensure that you have enough calories and nutrients for you and your baby.

Light exercise such as walking or swimming is also beneficial to support appropriate weight gain during pregnancy, and evidence suggests that this can make labour easier, remember to start off gradually and build up slowly. Exercising with somebody else, a family member, a friend or a group is a good way to keep yourself and others motivated.

I would continue to weigh yourself once a week, though six pounds sounds about right for 16 weeks, and if you are concerned you will be able to get further support from your midwife or GP.

NICE are currently preparing guidelines for appropriate weight gain in pregnancy. This document will look at all the scientific literature and make sound evidence based guidelines for women and health professionals to follow. This should help to ensure that women have clear information on the benefits of appropriate weight gain and the risks of too little or too much weight gain.