Within a few hours of birth, most babies are weighed as standard practice. The birth weight and the baby’s gestational age, which is the time between the conception and birth, are then logged in the baby’s medical record. The average birth weight is approximately 3.4kg (7.6 lbs.). Anything under 2.5kg (5.5 lbs.) is considered low birth weight, while a newborn weighing less than 1.5kg (3.3 lbs.) is classed as very low birth weight. Today, slightly more than 8% of newborns are recorded as having a low birth weight, with only 1.5% of babies weighing in at less than 1.5kg.
Since unborn babies gain most of their weight in the latter weeks of the pregnancy, premature birth is the main reason for a low birth weight. Any baby born before the completion of the normal gestation period of approximately 37 weeks has less time to grow and gain weight in the mother’s uterus and is therefore more likely to have a low birth weight. Another common reason for a low birth weight is a condition known as intra-uterine growth restriction (IUGR), which is when problems with the placenta, the mother’s health, or birth defects prevent the unborn baby from growing well in the uterus. A baby with IUGR born after a full-term pregnancy may be physically mature but weak, while a premature birth IUGR baby is likely to be physically immature and very small.
Additional factors that can lead to a low birth weight include:
A low birth weight puts newborns at greater risk of complications, and the risk of these complications increases in line with a decrease in the birth weight. As they are weaker, low birth weight babies are more susceptible to infection, and this is exacerbated because the lack of body fat makes it more difficult for them to keep warm. Even eating and gaining weight can be difficult, while low oxygen levels at birth and immature lungs can lead to respiratory problemssuch as respiratory distress syndrome. Additional risks for low birth weight babies include the following:
In almost every case, newborns with a low birth weight will need to stay in an Intensive Care Unit (ICU) until they have gained enough weight and are well enough to go home. In the ICU, the specialized attention they will receive includes round-the-clock monitoring, sleeping in a temperature controlled bed and being fed through a special tube. Thanks to the attention they receive, low birth weight babies between 1.5kg and 2.5kg (3.3lbs. and 5.5lbs.) now have a 95% chance of survival, and these babies will catch up with other babies and lead a normal life if there are no other complications.
As premature birth is the main cause of low birth weight, preventing premature births is the best way to prevent babies being born with a low birth weight. Prenatal care plays a very important role in achieving this because the health of both the mother and the fetus can be monitored regularly. Ultrasound is also used to measure the size of the fetus, which the measurement of fetus’s head and abdomen can then be compared against a growth chart to estimate fetal weight. In addition, it is important that the mother eats a healthful diet during pregnancy with the right amount of nutrition as maternal weight gain is directly linked with fetal weight gain and subsequent birth weight. Finally, mothers should avoid alcohol, cigarettes and illegal drugs during pregnancy as these also stunt fetal growth and lead to other complications.
Diploma of Thai Board of Pediatrics, Faculty of Medicine, Siriraj Hospital, Mahidol University, 2006