What to Know About Low Birth Weight?

Editor’s note: This is a guest post from James Tuck, a blogger on term.org.

Thank you to InterActive Health who invited me to come and discuss a topic that is near and dear to me. Today I am talking about Low Birth Weight and if it is a real health issue.

Everybody loves to hear about the good tidings and the blessings of a newborn baby. It is usually such an exciting time. Family drives into town, parties are thrown, and sleepless nights await. But what happens when everything doesn’t turn out the way you are expecting?

What happens if the baby is born weeks or months early. Should you be concerned if the birth weight of the baby is low even though they are born on time. Both situations fall under low birth weight.

Low birth weight can mean a lot of different things. Food for thought is it more medically concerning for low birth weight than high birth weight. I think most people agree low birth weight is more of a health concern.

If you’ve ever seen a baby born with low birth weight you know that they look small, malnourished, small, vulnerable, and small.

Let’s take a closer look at birth weight and how they are classified:

1.)  Normal Birth Weight  (NBW)  –  is when the baby is between 2500g to 4200g.
2.)  Low Birth Weight  (LBW)  –  is when the baby is less than 2500g or less than 5 lbs 8 oz.
3.)  Very Low Birth Weight  (VLBW)  –  is when the baby is less than 1500g.
4.)  Extremely Low Birth Weight  (ELBW)  –  is when the baby is less than 1000g.

*** g means grams ***

Two main categories of Low Birth Weight:

1.)  Preterm birth

2.)  Small for Gestational Age.

Both categories have Low Birth Weight in common but beyond that, there are far more differences than similarities.

For the purposes of this blog, Very low birth weight and Extremely low birth weight will be combined into Low Birth Weight alone.

Let’s take a look at both categories:

Small for Gestational Age

These are babies that are born around or near their expected due dates. And for some reason, they were born smaller in size than a normal baby for their sex and age. Remember, boys and girls have slightly different expectations for birth weight.

Birth weight is compared to a chart that identifies birth weight averages. From this chart, it is determined if they are normal weight. The weights are divided into percentages or percentiles. I am sure most everybody wants their child in the 90th percentile. But really, it’s just an average. The real concern is if a baby is in the bottom 10% for their age. This is where small for gestational age comes into play.

Causes for Small for Gestational Age

These may include the health of the mother, born in a developing country, nutrition of the mother, genetics, environmental, and others.

In some cases, IUGR or intrauterine growth retardation can be a direct link. This is when the fetus can not reach the potential size. In this case, an Ultrasound may help diagnosis this potential low birth weight problem.

Risk Factors

Specific risk factors leading to Small for Gestational Age may be categorized into a few areas: The baby, The mother, The Environment, or The placenta.

The risk factors affecting these ares include:

1.)  Environmental – Smoking, drug use, alcohol, or others
2.)  Infection
3.)  Diabetes Mellitus
4.)  Pre-eclampsia
5.)  Thrombophilia  – a tendency to thrombosis
6.)  Genetic variance
7.)  Multiple births
8.)  Connective tissue disorders
9.)  Damage to the Placenta
10.)  Physical assault
11.)  Others

Constitutionally Small

This is a term that describes a baby that is small for gestational age and in this case, there is nothing medically wrong with the baby. This aspect of the small for Gestational age is still part of the Low Birth Weight but less of a medical concern can be seen in these cases.

1/3 of all births that are categorized as Low Birth Weight are constitutionally small for their age.

There are Two Categories of Growth Restriction when looking at Small for Gestational Age

1.) Symmetrical

This is when the fetus has developed slowly throughout pregnancy.
The head circumference is proportionate to the body.
Causes may include: anemia, fetal alcohol syndrome, infections, and genetics.

2.) Asymmetrical

This is when the head grows normally, or close to normal, but the body grows much slower. This indicates that the embryo started out growing normally, but something, along the way, intervened.

It can be seen in chronically elevated blood pressure of the mother, malnutrition, some genetic changes, pre-eclampsia, placenta or umbilical cord problems, and others.

Treatment of Small for Gestational Age

Over ninety percent of babies catch up over the first two years of life.

The largest medical concern is called Failure-to-Thrive. This occurs when the baby can not continue to grow. Often the baby continues to loose weight or does not progress at a proper rate. In these cases, they do not catch up during the first two years of life unless an active treatment plan is put into place. Growth Hormone therapy may be an alternative for young children.

Additional testing and possible consulting for behavior, dietitian, Allergist, and other specialties are necessary because several medical issues can be affected by Low Birth Weight. Future problems with behavior and speaking can be expected in a large number of cases.

Preterm Birth

This occurs when the baby is born prior to 37 weeks of gestational age.

There are many reasons and causes for this to occur. Though, please remember that in some cases, the cause remains unknown. While in other cases, more than one cause can be identified.

Another term for Preterm birth is Premature birth. This refers to the birth of the baby with resulting poorly or underdeveloped organs. Premature births are at an increased risk for long and short-term medical conditions. In some ways, the wording, premature births have fallen out of favor. I will use only Preterm from this point forward.

Several organs mature between weeks 34 and 37. The lungs are an organ that is often greatly affected by a preterm birth. Drugs, incubation, and other treatment steps are placed to help allow the organs to develop over time.

Occasionally a ventilator is required to help the Preterm breathe properly.

Medical Risks of Preterm Birth

Preterm children have an increased risk of death during the first year of life. Most of the time, death occurs within the first month. Around the world, almost 500,000 deaths can be attributed to preterm births.

Infections, health damage, organ problems, breathing difficulty, and overall health is the medical risks associated with preterm births.

Other risks:

–  Cerebral palsy
–  Brain bleeding
–  Cognitive dysfunction
–  Language problems
–  Heart problems
–  Respiratory distress
–  Respiratory Failure
–  Chronic Lung disease
–  Abdominal pain
–  Rickets
–  Blood sugar problems
–  Infections
–  Sepsis
–  Pneumonia
–  Hernias
–  Jaundice
–  Anemia
–  Learning Disabilities
–  Speech problems
–  Behavior problems
–  Allergies
–  And many other problems

Limit of Viability

This is an important number in the medical community that refers to the chance of survival. It is when a baby is given a 50% chance of survival. It is based on a gestational age.

Over the last four decades, the age of the baby who survives, in number of weeks, has decreased dramatically. This means that children have a better chance of living at a younger age.

Currently the age is around 24 weeks of age. This means that 50% of the cases will live and 50% of them will not. There are cases of infants living from 21 weeks of age. But these cases are very rare.

Causes of Preterm Delivery

Again, cause of preterm can be wide, varied, and/or unknown. It can be difficult to isolate a cause and over fifty percent of preterm births, the cause is never determined.

Childbirth or Labor is long and a complex process. There are many factors that work together. Problems or causes could be from the environment, the mother, the baby and other.


If the mother is a cause factor, many risks may come into play.

Age:  if a mother is older or younger a greater risk is present. Over age 35 or younger than 18 may be a risk

Weight and Height: This could be a risk

Race:  Black women have preterm birth rate twice that of a white women. But Asian or Hispanic women don’t necessarily have a higher preterm birth rate. Therefore the real risk of race is unknown.

Time in-between pregnancies: 6 month or less span have a preterm birth rate that is twice as high.

Work, activity level, stress and other also have been looked at for risk factors.

Previously surgically induced abortions may have a slightly higher rate.

Poor nutrition can be a cause factor.

Very low BMI has an increased risk.

Previous medical condition such as Diabetes, hypertension and several other medical issues are a large risk factor and will increase the preterm birth rate.

Some studies show unmarried mothers have a slightly higher rate than married mothers.

Genetics is another factor

Factors associated with Pregnancy

Multiple pregnancies are a large or significant factor in preterm births. Over 50% of twins are born preterm. Triplets and more are even higher in preterm birth rates.

Fertility medication, high blood pressure during pregnancy alone, pre-eclampsia, heart disease and other medical conditions brought on by pregnancy are risks.

Problems with the placenta including placenta previa or placental abruption can also be large risk factors for preterm delivery.

Anxiety, Depression, tobacco use, drug abuse, alcohol abuse are things that can induce labor in some cases. These can be directly related to problems during pregnancy and preterm births.

Fetus or Preterm baby

Infection of the child or mother can be a large reason for preterm births. Typically this can occur from intrauterine infections, genital infections, amniotic fluid infection and fetus infections.

Genetic changes to the baby can cause a slight increase in risk for early birth.

Need for Medical care and Screening

Careful monitoring of the mother or child at risk is a great way to prevent or prepare for a Preterm delivery. Ultrasounds, Blood work, physical exam, and discussion of risks and symptoms should be done with a primary care physician or an OBGYN.

Knowledge of your own health care issues are essential. The use of proper medications to treat the disease can decrease the overall risk. Self care of proper nutrition, low stress, stopping of alcohol, drug or tobacco use.

If you are at risk for preterm births, stay close to medical providers and often more than one ultrasound and blood work will be in your future.

What to look for in the future

Children surviving a preterm birth will have outcomes that vary. No symptoms or problems stemming from the preterm birth are seen in many cases.

Other children suffer from behavioral, speech, hearing, and other similar problems.

Some long term medical problems are seen in some cases. Seizures, mental retardation, cerebral palsy and other medical conditions will be life long and difficult.

Some Interesting Data

Earliest known premature baby to survive:

1.) James Gill – Ottawa Canada

Born in 1987 – 21 weeks and 5 days
Weight – 1lb and 6 ounces

2.)  Amillia Taylor – Miami Florida

Born 2006 – 21 weeks and 6 days
Weight – 10 ounces

Smallest Baby to survive

1.)  Madeline Mann  –  born 26 weeks – 9.9 ounces
2.)  Rumaisa Rahman  –  born 25 weeks – 8.6 ounces –  September 2004

Smallest Baby Boy to survive

1.)  Jonathon Whitehill  –  born 25 weeks  –  10.9 ounces

-Author’s Bio-
James has a bachelor degree in Biology, with a professional background in micro-organisms, artificial selection, and lab research. James currently divides his time between blogging on term.org (a health insurance website), and wrestling with his three small boys.


  1. ^“World’s Smallest Baby Goes Home, Cellphone-Sized Baby Is Discharged From Hospital”. CBS News. 2005-02-08. http://www.cbsnews.com/stories/2005/02/08/health/main672488.shtml..
  2. ^ “World’s Smallest Baby Goes Home”. CBS News. 8 February 2005. http://www.cbsnews.com/stories/2005/02/08/health/main672488.shtml.
  3. ^ “The Tiniest Babies”. University of Iowa. http://www.medicine.uiowa.edu/tiniestbabies/bworder.asp?gender=Male.
  4. Richard E. Behrman, Adrienne Stith Butler, Editors, Committee on Understanding Premature Birth and Assuring Healthy Outcomes. Preterm Birth: Causes, Consequences, and Prevention. Institute of Medicine. The National Academies Press, 2007.
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