One of the causes is low maternal weight gain. So, you are wise to be aware that you need to gain an appropriate amount of weight for the sake of your baby. Researchers looking at two separate groups of women, found that low weight gain in early pregnancy wasn't related to an increase in IUGR, but it was during the second two trimesters. Further confirming the fact that when you gain the weight is important, they noticed that IUGR occurred in women with normal weight gain during the entire pregnancy but low weight gain during the second or third trimester. So if you should not be able to get adequate nutrition during either the second or third trimester you may be putting your baby at risk.
Morning sickness can be a real deterrent to weight gain during the first trimester.
However, that needn't be a concern. Usually morning sickness lessens during the second trimester and appetite returns so that you will feel more like eating. During the beginning of the second trimester, if you find that morning sickness is continuing to prevent you from eating and drinking appropriately, you should speak with your midwife or doctor about treatment. Findings further confirm the risk that dieting during pregnancy may have. Failing to gain the recommended amount of weight in order to 'diet' may be putting your baby at a real risk for lifelong health problems.