Under-weight babies are also termed as LBW – low birth weight babies. The gestation period for humans is approximately nine months. The ideal human baby weight at birth is 2.5kg to 4kg. Babies born under 2.5kg (5.5 pounds) are considered as low birth weight or under weight babies.
A healthy birth weight is extremely important for newborn. This is because, babies birth with low birth weight are more susceptible to have health problem, slower development, delayed milestones and low immunity.
There are lot many reasons that can cause the low birth weight to baby. The first reason stands is premature delivery due to some reason. If the baby is delivered prior to the expected date and the normal gestational period (37 weeks of pregnancy) is generally born with low birth weight.
Babies do have low birth weight if they are born too soon or if they are small for their gestational age. This could be the result of mal or undernourishment of the mother. In other words, if the mother does not receive good amount of nutrients during her pregnancy, the baby may not receive the proper nourishment and that may end up in the low birth weight.
Low weight babies are always at risks. Most of the babies do not have enough strength to suck properly and therefore, it is quite difficult for them to get breastfeeding. The babies require rich supplement of proteins, Vitamins, fats and other nutrients that is presented in the breastmilk. This supplement is cut-off because the baby’s sucking reflex is not much and low birth infant often gets tired after two-three sucks.
Low-birth weight babies can have life-long health problem. They can have underdeveloped body systems such as cardiovascular, digestive and excretory systems. Low-birth weight babies have less immunity power and therefore, they are more susceptible to have infections even with minor exposure to microorganisms.
The survey says that low birth weight babies have short life span and many of them die within first year of their lives. Low-birth weight babies may have respiratory problems and therefore may require ventilator and other life supporting systems to survive on the initial stages. They are also prone to develop neonatal icterus (jaundice) and anemia due to malnourishment. 
If the survive, they will be having delayed milestones such as crawling, sitting, teething, standing, running and so on. They may look smaller to their age as compare to healthy and normal babies.
Low-weight babies require extra attention and care. They are not given to anyone until they gain normal weight. Bathing, feeding, clothing and all the routine activities are to be performed with great care for babies having low birth weight. They are to be supplied with extra nutrients and tonics form outside (in the form of medicines) like folic acid, calcium, iron and Vitamins.
Due to low-birth weight, the vaccination period also get disturbed. There will be delayed schedule for a preterm or LBW babies and therefore, they are one more time, exposed to the infections and more susceptible to get infected.
Prevention is proper nourishment to the mother. The entire period of pregnancy, the mother is to be supplied with carbohydrates, Vitamins, minerals and other important factors/conditions. The mother should not lift the weight during the pregnancy period, she should avoid smoking, drinking alcohol and other junk foods that can harm the body. She should take care that she should not fall down and must avoid any kind of injury to her.
Once the baby is born with low-birth weight, there is nothing you can do except nourishing the baby and supplying all the nutrients. The baby can be given glucose and other electrolytes intravenously. The child is probably to be kept in incubators and needs treatment if it has some complications like respiratory distress or jaundice.
Once, the child is handed over to parents, extreme care is to be taken to bring the child up healthily. The baby is to be supplied with vitamins, iron, folic acid, calcium and different healthy tonics. The baby is not exposed to relatives, friends and any other people except the parents. Extra hygienic condition is required.