HOME

TheInfoList



OR:

Low birth weight (LBW) is defined by the World Health Organization as a
birth weight Birth weight is the body weight of a baby at its birth. The average birth weight in babies of European descent is , with the normative range between . On average, babies of South Asian and Chinese descent weigh about . As far as low birth weigh ...
of an infant of or less, regardless of gestational age. Infants born with LBW have added health risks which require close management, often in a neonatal intensive care unit (NICU). They are also at increased risk for long-term health conditions which require follow-up over time.


Classification

Birth weight may be classified as: * High birth weight (
macrosomia Large for gestational age (LGA) is a term used to describe infants that are born with an abnormally high weight, specifically in the 90th percentile or above, compared to other babies of the same developmental age. Macrosomia is a similar term tha ...
): greater than * Normal weight (term delivery): * Low birth weight: less than ** Very low birth weight: less than ** Extremely low birth weight: less than


Causes

LBW is either caused by
preterm birth Preterm birth, also known as premature birth, is the birth of a baby at fewer than 37 weeks gestational age, as opposed to full-term delivery at approximately 40 weeks. Extreme preterm is less than 28 weeks, very early preterm birth is between ...
(that is, a low gestational age at birth, commonly defined as younger than 37 weeks of gestation) or the infant being
small for gestational age Small for gestational age (SGA) newborns are those who are smaller in size than normal for the gestational age, most commonly defined as a weight below the 10th percentile for the gestational age. Causes Being small for gestational age is broadly ...
(that is, a slow prenatal growth rate), or a combination of both. In general, risk factors in the mother that may contribute to low birth weight include young ages, multiple pregnancies, previous LBW infants, poor nutrition, heart disease or hypertension, untreated
celiac disease Coeliac disease (British English) or celiac disease (American English) is a long-term autoimmune disorder, primarily affecting the small intestine, where individuals develop intolerance to gluten, present in foods such as wheat, rye and barle ...
, substance use disorder, excessive alcohol use, and insufficient prenatal care. It can also be caused by
prelabor rupture of membranes Prelabor rupture of membranes (PROM), previously known as premature rupture of membranes, is breakage of the amniotic sac before the onset of labor. Women usually experience a painless gush or a steady leakage of fluid from the vagina. Complicati ...
. Environmental risk factors include smoking, lead exposure, and other types of air pollutions.


Preterm birth

The mechanism of preterm birth is heterogeneous and poorly understood. It may be tied to one or more of the following processes: premature fetal endocrine activation, intrauterine inflammation, over-distension of the uterus, and endometrial bleeding. A prominent risk factor for preterm birth is prior history of preterm delivery. However, there is no reliable protocol for screening and prevention of preterm birth.


Small for gestational age

Infants born small for gestational age may be constitutionally small, with no associated pathologic process. Others have intrauterine growth restriction (IUGR) due to any of various pathologic processes. Babies with
chromosomal abnormalities A chromosomal abnormality, chromosomal anomaly, chromosomal aberration, chromosomal mutation, or chromosomal disorder, is a missing, extra, or irregular portion of chromosomal DNA. These can occur in the form of numerical abnormalities, where the ...
or other
congenital anomalies A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can r ...
may manifest IUGR as part of their syndrome. Problems with the placenta can prevent it from providing adequate oxygen and nutrients to the fetus, resulting in growth restriction. Infections during pregnancy that affect the fetus, such as rubella, cytomegalovirus, toxoplasmosis, and
syphilis Syphilis () is a sexually transmitted infection caused by the bacterium ''Treponema pallidum'' subspecies ''pallidum''. The signs and symptoms of syphilis vary depending in which of the four stages it presents (primary, secondary, latent, and ...
, may also affect the baby's weight.


Environmental factors

Maternal tobacco smoking doubles risk of LBW for the infant. More recently, passive maternal smoking has been examined for possible effects on birth weight, and has been shown to increase risk of LBW by 16%.


Air pollutants

The combustion products of solid fuel in developing countries can cause many adverse health issues in people. Because a majority of pregnant women in developing countries, where rate of LBW is high, are heavily exposed to indoor air pollution, increased relative risk translates into substantial population attributable risk of 21% of LBW.
Particulate matter Particulates – also known as atmospheric aerosol particles, atmospheric particulate matter, particulate matter (PM) or suspended particulate matter (SPM) – are microscopic particles of solid or liquid matter suspended in the air. The te ...
, a component of ambient
air pollution Air pollution is the contamination of air due to the presence of substances in the atmosphere that are harmful to the health of humans and other living beings, or cause damage to the climate or to materials. There are many different type ...
, is associated with increased risk of low birth weight. Because particulate matter is composed of extremely small particles, even nonvisible levels can be inhaled and present harm to the fetus. Particulate matter exposure can cause inflammation, oxidative stress, endocrine disruption, and impaired oxygen transport access to the placenta, all of which are mechanisms for heightening the risk of low birth weight. To reduce exposure to particulate matter, pregnant women can monitor the EPA’s
Air Quality Index An air quality index (AQI) is used by government agencies to communicate to the public how polluted the air currently is or how polluted it is forecast to become. AQI information is obtained by averaging readings from an air quality sensor, whi ...
and take personal precautionary measures such as reducing outdoor activity on low quality days, avoiding high-traffic roads/intersections, and/or wearing personal protective equipment (i.e., facial mask of industrial design). Indoor exposure to particulate matter can also be reduced through adequate ventilation, as well as use of clean heating and cooking methods. A correlation between maternal exposure to
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simpl ...
(CO) and low birth weight has been reported that the effect on birth weight of increased ambient CO was as large as the effect of the mother smoking a pack of cigarettes per day during pregnancy. It has been revealed that adverse reproductive effects (e.g., risk for LBW) were correlated with maternal exposure to CO emissions in Eastern Europe and North America. Mercury is a known toxic heavy metal that can harm fetal growth and health, and there has been evidence showing that exposure to mercury (via consumption of large
oily fish Oily fish are fish species with oil (fats) in soft tissues and in the coelomic cavity around the gut. Their fillets may contain up to 30% oil, although this figure varies both within and between species. Examples of oily fish include smal ...
) during pregnancy may be related to higher risks of LBW in the offspring.


Other exposures

Elevated blood lead levels in pregnant women, even those well below the US
Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georg ...
's 10 ug/dL "level of concern", can cause
miscarriage Miscarriage, also known in medical terms as a spontaneous abortion and pregnancy loss, is the death of an embryo or fetus before it is able to survive independently. Miscarriage before 6 weeks of gestation is defined by ESHRE as biochemical lo ...
,
premature birth Preterm birth, also known as premature birth, is the birth of a baby at fewer than 37 weeks gestational age, as opposed to full-term delivery at approximately 40 weeks. Extreme preterm is less than 28 weeks, very early preterm birth is between ...
, and LBW in the offspring. Exposure of pregnant women to airplane noise was found to be associated with low birth weight via adverse effects on fetal growth. Prevalence of low birth weight in Japan is associated with radiation doses from the Fukushima accidents of March 2011.


Periodontal health

Low birth weight, preterm birth and preeclampsia have been associated with maternal
periodontal disease Periodontal disease, also known as gum disease, is a set of inflammatory conditions affecting the tissues surrounding the teeth. In its early stage, called gingivitis, the gums become swollen and red and may bleed. It is considered the main caus ...
, though the strength of the observed associations is inconsistent and varies according to the population studied, the means of periodontal assessment and the periodontal disease classification employed. The risk of low birth weight can be reduced with treatment of the periodontal disease. This therapy is safe during pregnancy and reduces the inflammatory burden, thus decreasing risk for preterm birth and low birth weight.


Management


Temperature regulation

LBW newborns are at increased risk of hypothermia due to decreased
brown fat Brown adipose tissue (BAT) or brown fat makes up the adipose organ together with white adipose tissue (or white fat). Brown adipose tissue is found in almost all mammals. Classification of brown fat refers to two distinct cell populations with si ...
stores. Plastic wraps, heated pads, and skin-to-skin contact decrease risk of hypothermia immediately after delivery. One or more of these interventions may be employed, though combinations incur risk of hyperthermia. Warmed incubators in the NICU aid in thermoregulation for LBW infants.


Fluid and electrolyte balance

Frequent clinical monitoring of volume status and checking of serum electrolytes (up to three times daily) is appropriate to prevent dehydration, fluid overload, and electrolyte imbalance. VLBW newborns have an increased body surface to weight ratio, increasing risk for insensible fluid losses and dehydration. Humidified incubators and skin emollients can lessen insensible fluid loss in VLBW newborns. However, fluid overloading is not benign; it is associated with increased risk of congestive heart failure, necrotizing enterocolitis, and mortality. A degree of fluid restriction mitigates these risks. VLBW newborns are at risk for electrolyte imbalances due to the relative immaturity of the
nephron The nephron is the minute or microscopic structural and functional unit of the kidney. It is composed of a renal corpuscle and a renal tubule. The renal corpuscle consists of a tuft of capillaries called a glomerulus and a cup-shaped structure c ...
s in their kidneys. The kidneys are not equipped to handle large sodium loads. Therefore, if normal saline is given, the sodium level may become elevated, which may prompt the clinician to give more fluids. Sodium restriction has been shown to prevent fluid overload. Potassium must also be monitored carefully, as immature
aldosterone Aldosterone is the main mineralocorticoid steroid hormone produced by the zona glomerulosa of the adrenal cortex in the adrenal gland. It is essential for sodium conservation in the kidney, salivary glands, sweat glands, and colon. It plays a c ...
sensitivity and sodium-potassium pumping increases risk for
hyperkalemia Hyperkalemia is an elevated level of potassium (K+) in the blood. Normal potassium levels are between 3.5 and 5.0mmol/L (3.5 and 5.0mEq/L) with levels above 5.5mmol/L defined as hyperkalemia. Typically hyperkalemia does not cause symptoms. Occa ...
and cardiac
arrhythmia Arrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or dysrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. A resting heart rate that is too fast – above 100 beats per minute in adults ...
s. VLBW newborns are frequently found to have a persistently patent ductus arteriosus (PDA). If present, it is important to evaluate whether the PDA is causing increased circulatory volume, thus posing risk for heart failure. Signs of clinically significant PDA include widened pulse pressure and bounding pulses. In newborns with significant PDA, fluid restriction may avoid the need for surgical or medical therapy to close it.


Approach to nutrition

As their gastrointestinal systems are typically unready for enteral feeds at the time of birth, VLBW infants require initial parenteral infusion of fluids, macronutrients, vitamins, and micronutrients.


Energy needs

Decreased activity compared to normal weight newborns may decrease energy requirements, while comorbidities such as bronchopulmonary dysplasia may increase them. Daily weight gain can reveal whether a VLBW newborn is receiving adequate calories. Growth of 21 g/kg/day, mirroring ''in utero'' growth, is a target for VLBW and ELBW neonates.


Enteral sources

Upon transitioning to enteral nutrition,
human milk Breast milk (sometimes spelled as breastmilk) or mother's milk is milk produced by mammary glands located in the breast of a human female. Breast milk is the primary source of nutrition for newborns, containing fat, protein, carbohydrates ( lact ...
is preferable to formula initially in VLBW newborns because it speeds up development of the intestinal barrier and thereby reduces risk of necrotizing enterocolitis, with an
absolute risk reduction The risk difference (RD), excess risk, or attributable risk is the difference between the risk of an outcome in the exposed group and the unexposed group. It is computed as I_e - I_u, where I_eis the incidence in the exposed group, and I_u is th ...
of 4%. Donor human milk and maternal expressed breast milk are both associated with this benefit. One drawback of human milk is the imprecision in its calorie content. The fat content in human milk varies greatly among women; therefore, the energy content of human milk cannot be known as precisely as formula. Each time human milk is transferred between containers, some of the fat content may stick to the container, decreasing the energy content. Minimizing transfers of human milk between containers decreases the amount of energy loss. Formula is associated with greater linear growth and weight gain than donor breast milk in LBW infants.


Individual nutrient considerations

VLBW newborns are at increased risk for
hypoglycemia Hypoglycemia, also called low blood sugar, is a fall in blood sugar to levels below normal, typically below 70 mg/dL (3.9 mmol/L). Whipple's triad is used to properly identify hypoglycemic episodes. It is defined as blood glucose belo ...
due to decreased energy reserves and large brain mass to body mass ratio. Hypoglycemia may be prevented by intravenous infusion of glucose, amino acids, and lipids. These patients are also at risk of
hyperglycemia Hyperglycemia is a condition in which an excessive amount of glucose circulates in the blood plasma. This is generally a blood sugar level higher than 11.1  mmol/L (200  mg/dL), but symptoms may not start to become noticeable until even ...
due to immature insulin secretion and sensitivity. However, insulin supplementation is not recommended due to the possible adverse effect of hypoglycemia, which is more dangerous. VLBW newborns have increased need for amino acids to mirror ''in utero'' nutrition. Daily protein intake above 3.0 g/kg is associated with improved weight gain for LBW infants. ELBW newborns may require as much as 4 g/kg/day of protein. Due to the limited solubility of
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...
and phosphorus in parenteral infusions, VLBW infants receiving parenteral nutrition will be somewhat deficient of these elements and will require clinical monitoring for
osteopenia Osteopenia, known as "low bone mass" or "low bone density", is a condition in which bone mineral density is low. Because their bones are weaker, people with osteopenia may have a higher risk of fractures, and some people may go on to develop osteop ...
.


Hematology

One Cochrane review showed administration of erythropoietin (EPO) decreases later need for
blood transfusion Blood transfusion is the process of transferring blood products into a person's circulation intravenously. Transfusions are used for various medical conditions to replace lost components of the blood. Early transfusions used whole blood, but mo ...
s, and also is associated with protection against necrotizing enterocolitis and
intraventricular hemorrhage Intraventricular hemorrhage (IVH), also known as intraventricular bleeding, is a bleeding into the brain's ventricular system, where the cerebrospinal fluid is produced and circulates through towards the subarachnoid space. It can result from phys ...
. EPO is safe and does not increase risk of mortality or retinopathy of prematurity.


Prognosis


Perinatal outcomes

LBW is closely associated with fetal and
perinatal mortality Perinatal mortality (PNM) refers to the death of a fetus or neonate and is the basis to calculate the perinatal mortality rate. Variations in the precise definition of the perinatal mortality exist, specifically concerning the issue of inclusion o ...
and morbidity, inhibited growth and cognitive development, and chronic diseases later in life. At the population level, the proportion of babies with a LBW is an indicator of a multifaceted public-health problem that includes long-term maternal malnutrition, ill health, hard work and poor health care in pregnancy. On an individual basis, LBW is an important predictor of newborn health and survival and is associated with higher risk of infant and childhood mortality. Low birth weight constitutes as sixty to eighty percent of the
infant mortality Infant mortality is the death of young children under the age of 1. This death toll is measured by the infant mortality rate (IMR), which is the probability of deaths of children under one year of age per 1000 live births. The under-five morta ...
rate in developing countries. Infant mortality due to low birth weight is usually directly causal, stemming from other medical complications such as preterm birth, PPROM, poor maternal nutritional status, lack of prenatal care, maternal sickness during pregnancy, and an unhygienic home environment.


Long term outcomes

Hyponatremia in the newborn period is associated with neurodevelopmental conditions such as spastic
cerebral palsy Cerebral palsy (CP) is a group of movement disorders that appear in early childhood. Signs and symptoms vary among people and over time, but include poor coordination, stiff muscles, weak muscles, and tremors. There may be problems with sensat ...
and sensorineural hearing loss. Rapid correction of hyponatremia (faster than 0.4 mEq/L/hour) perinatally is also associated with neurodevelopmental adverse effects. Among VLBW children, risk for cognitive impairment is increased with lower birth weight, male sex, nonwhite ethnicity, and lower parental education level. There is no clear association between brain injury in the neonatal period and later cognitive impairment. Additionally, low birth weight has associations with cardiovascular diseases later in life, especially in cases of large increases in weight during childhood.


Epidemiology

The World Health Organization (WHO) estimates the worldwide prevalence of low birth weight at 15% as of 2014, and varies by region: Sub-Saharan Africa, 13%; South Asia, 28%; East Asia and the Pacific, 6%; Latin America and the Caribbean, 9%. Aggregate prevalence of LBW in
United Nations The United Nations (UN) is an intergovernmental organization whose stated purposes are to maintain international peace and security, develop friendly relations among nations, achieve international cooperation, and be a centre for harmonizi ...
-designated Least Developed Countries is 13%. The WHO has set a goal of reducing worldwide prevalence of LBW by 30% through public health interventions including improved prenatal care and women's education. In the United States, the
Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georg ...
(CDC) reports 313,752 LBW infants in 2018, for a prevalence of 8.28%. This is increased from an estimated 6.1% prevalence in 2011 by the
Agency for Healthcare Research and Quality The Agency for Healthcare Research and Quality (AHRQ; pronounced "ark" by initiates and often "A-H-R-Q" by the public) is one of twelve agencies within the United States Department of Health and Human Services (HHS). The agency is headquartered ...
(AHRQ).Kowlessar N.M., Jiang H.J., and Steiner C. Hospital Stays for Newborns, 2011. HCUP Statistical Brief #163. October 2013. Agency for Healthcare Research and Quality, Rockville, MD

The CDC reported prevalence of VLBW at 1.38% in 2018, similar to the 2011 AHRQ estimate.


References

{{Authority control Human body weight Disorders related to length of gestation and fetal growth Pediatrics Women's health