Low Birth Weight in Babies: Causes, Risk Factors, and Impacts

Low birth weight (LBW) is defined as a baby born weighing less than 5 pounds, 8 ounces (2,500 grams). Babies born with LBW account for around 1 in 12 births in the United States. Low birth weight can be caused by preterm birth, fetal growth restriction, genetics, maternal health issues, infections, and other factors. Babies born with LBW are at higher risk for health complications like respiratory distress, feeding difficulties, neurological issues, and sudden infant death syndrome (SIDS). However, medical advances have allowed more low birth weight babies to survive and thrive.

Causes of Low Birth Weight

The main causes of low birth weight are:

  • Preterm Birth: Babies born before 37 weeks gestation have less time to grow and gain weight in the womb, resulting in LBW. The earlier the birth, the lower the birth weight is likely to be.
  • Fetal Growth Restriction: Also called intrauterine growth restriction (IUGR), this means the fetus does not grow adequately in the womb due to placental insufficiency, the mother’s health, infections, or birth defects. This can restrict growth and result in LBW.
  • Genetics: Some babies are genetically predisposed to be smaller. Small parents tend to have smaller babies.
  • Slowed Growth: Some babies experience slowed growth during pregnancy for unclear reasons, leading to LBW.
  • Multiple Pregnancy: Over half of twins and higher-order multiples are born with LBW due to crowded uterine space and nutritional demands.
  • Maternal Health Issues: Chronic conditions like hypertension, heart disease, and diabetes can increase the risk of LBW.

Risk Factors for Low Birth Weight

Risk factors that can contribute to having a LBW baby include:

  • Preterm Labor: Delivering before 37 weeks greatly increases the chance of LBW.
  • Maternal Age: Teen moms under 15 and older moms over 35 have higher LBW risks.
  • Chronic Diseases: Conditions like high blood pressure, diabetes, heart/lung disease.
  • Medications: Drugs for chronic illnesses, epilepsy, blood clots.
  • Prior LBW Baby: Having had one LBW baby increases your risk of having another.
  • Infections: STIs, rubella, cytomegalovirus, and others can impair fetal growth.
  • Environmental Exposures: Air pollution, lead exposure, smoking, and drug use.
  • Poor Nutrition: Inadequate weight gain, malnutrition during pregnancy.
  • Abuse: Physical, emotional, or sexual abuse can impact fetal growth.
  • Race: Systemic racial healthcare inequities mean Black women have double the rate of LBW compared to White women.

Impacts of Low Birth Weight

While medical advances have enabled more low birth weight babies to survive and thrive, LBW can impact development:

  • Physical Development: LBW babies may experience delayed motor skills, muscle development, and growth milestones.
  • Neurodevelopment: Higher risks of cognitive deficits, learning disabilities, ADHD, cerebral palsy, and impairments in executive function. The earlier the birth, the higher the risks.
  • Immune System: LBW babies have underdeveloped immune systems, making them susceptible to infections.
  • Feeding: Weak suckling reflexes and oral muscle control can make feeding challenging. Difficulty gaining weight.
  • Thermoregulation: Harder for LBW babies to stay warm due to higher surface area to body mass ratio.
  • Vision and Hearing: Higher risks of vision impairment, retinal damage, and hearing loss.

However, the majority of LBW babies catch up developmentally and have normal long-term outcomes. Outcomes depend on the individual child.

Complications from Low Birth Weight

LBW babies are at risk for numerous medical complications:

  • Respiratory Distress Syndrome: Underdeveloped lungs can cause life-threatening breathing problems.
  • Jaundice: Excess bilirubin in the blood causes yellowing of the skin and eyes.
  • Hypoglycemia: Inability to maintain proper blood sugar levels.
  • Necrotizing Enterocolitis: Serious intestinal infection.
  • Feeding Problems: Weak sucking, poor weight gain, and difficulty feeding.
  • Temperature Instability: Challenges maintaining a normal body temperature.
  • Infection: Immature immune system cannot fight infections well.
  • Anemia: Having too few red blood cells, often requiring transfusions.
  • Neurological Issues: Bleeding, fluid buildup, and damage in the brain.
  • Heart Problems: Patent ductus arteriosus, a defect in the vessels near the heart.
  • Retinopathy of Prematurity: Abnormal blood vessel growth in eyes that can cause vision loss.
  • SIDS: Low birth weight is a risk factor for sudden infant death syndrome.

NICU Care for Low Birth Weight Babies

Many low birth weight babies require care in the neonatal intensive care unit (NICU). NICU care for LBW babies may involve:

  • Incubators: Provides warmth and humidity to help LBW babies maintain their body temperature.
  • Ventilators: Breathing machines to help underdeveloped lungs.
  • Feeding Tubes: Delivers nutrition through tubes inserted in the nose/mouth or directly into the stomach if needed.
  • IV Fluids: Provides hydration and nutrients through intravenous catheters.
  • Monitors: Tracks breathing, heart rate, blood pressure, temperature, oxygen saturation.
  • Phototherapy: Special lights help treat jaundice in LBW babies.
  • Medications: Antibiotics, blood pressure drugs, and others may be prescribed.
  • Surgery: To repair heart defects, bleeding in the brain, or other complications.

Preventing Low Birth Weight

While not always preventable, the following can help reduce the risk of having a LBW baby:

  • Get Early and Regular Prenatal Care: Helps monitor baby’s growth and manage maternal health conditions.
  • Maintain a Healthy Diet: Eat a balanced diet with plenty of nutrients to support fetal growth.
  • Gain Appropriate Weight: Discuss recommended weight gain at prenatal visits.
  • Take Prescribed Vitamins: Especially folic acid before and during pregnancy.
  • Avoid Smoking, Drinking, Drugs: Cigarette smoke, alcohol and illicit drugs impair development.
  • Control Existing Health Conditions: Follow doctor’s advice for chronic diseases like diabetes.
  • Reduce Stress: High stress levels release hormones that can restrict fetal growth.
  • Avoid Environmental Hazards: Secondhand smoke, lead, air pollution, toxic chemicals.
  • Treat Infections Promptly: STIs, UTIs and other infections can affect the baby.

FAQs About Low Birth Weight

  1. What is considered a low birth weight baby?

Babies born weighing less than 5 pounds, 8 ounces (2,500 grams) are considered low birth weight. Normal birth weights range from 5 lbs, 8 oz to 8 lbs, 13 oz.

  1. What causes babies to be born with low birth weight?

The main causes are preterm birth before 37 weeks, fetal growth restriction in the womb, genetic factors, maternal health problems, infections, and lifestyle factors like smoking and drug use.

  1. How does low birth weight affect babies?

It increases the risk of complications and developmental issues, especially neurological, respiratory, feeding, and immune system problems. Outcomes depend on the child, but most catch up developmentally.

  1. Do low birth weight babies have health issues?

Yes, LBW babies are at higher risk for breathing trouble, hypoglycemia, infections, jaundice, feeding issues, cerebral palsy, and other complications, especially right after birth.

  1. Do low birth weight babies need NICU care?

Frequently yes, LBW babies often require specialized neonatal intensive care for issues like immature lungs, inability to stay warm, feeding difficulties, infections, and breathing issues.

  1. How can I reduce the risk of having a low birth weight baby?

Get early prenatal care, eat healthy, gain appropriate weight, take prenatal vitamins, exercise moderately, reduce stress, avoid smoking/drinking/drugs, and treat any infections promptly.

  1. What percentage of babies are born with low birth weight?

Around 8% of babies in the U.S. are born with low birth weight, meaning less than 5 lbs, 8 oz. Rates are higher among Black women (14%) than White women (7%).

  1. Can low birth weight cause learning disabilities?

Yes, LBW babies are at increased risk for cognitive deficits, learning disabilities, attention issues, delayed development and impairments in executive function later in childhood.

  1. How can I help my low birth weight baby develop normally?

Follow your pediatrician’s guidance, attend regular well-child checks, participate in physical/occupational therapy, minimize infections, provide lots of affection, read together, and maintain routines.

  1. Will my low birth weight baby eventually catch up in growth?

In most cases, yes. LBW babies are often smaller than peers as infants but the majority catch up to normal heights and weights by 2 years old with proper nutrition and healthcare.

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