Low birth weight and Cardio-respiratory fitness

Low birth weight and cardio-respiratory health

Getting easily out of breath? It may be because you may be relatively smaller at birth than normal. The average birth weight for babies is around 7.5 lb (3.5 kg)? In India, the normal weight of a new-born is between 2.5 kg to 3.5 kg.

If a baby has a birth weight more than 4 kg, regardless of gestational age, might increase the risk of childhood obesity and other metabolic syndromes like high blood pressure, diabetes, cholesterol abnormality, etc in later life.

Similarly, when a baby born weighing less than 2.5 kg, regardless of gestational age, are considered as low birth weight. Today’s writing will highlight the complications of it during adulthood.


The researchers believe the findings are of significance to public health, seeing as about 15% of babies born globally weigh less than 2.5 kilos at birth. A low birth weight baby’s head look bigger than rest of his/her body and body looks thin.

  • It is considered that baby gains weight in the mother’s womb and much of it during last weeks of pregnancy. Due to premature birth i.e. before 37 weeks of pregnancy, the baby cannot gain weight in the womb for enough days.
  • Sometimes, baby does not grow well during pregnancy due to the problems with placenta, the mother’s health, or baby’s health. 
  • Mother’s age : Teen mothers (younger than 15 years old) or the age of a mother more than 35.
  • History of premature pregnancy.
  • Babies of mother’s giving multiple birth may have higher risk of low birth weight child.


The baby’s tiny body is not as strong as a baby of normal birth weight. He or she may have a harder time eating, gaining weight, and fighting infection. Premature babies often have a hard time staying warm because they don’t have much fat on their bodies(1).

In general, the lower the birth weight, the greater the risk for complications. Some of the common problems may include:

  • Low oxygen levels at birth
  • Trouble staying warm
  • Trouble feeding and gaining weight
  • Infection
  • Breathing problems and immature lungs (infant respiratory distress syndrome)
  • Nervous system problems, such as bleeding inside the brain (intraventricular hemorrhage)
  • Digestive problems, such as serious inflammation of the intestines (necrotizing enterocolitis)
  • Sudden infant death syndrome (SIDS)

Low birth weight and Cardio-respiratory fitness

Cardio-respiratory (CRF) fitness refers to the ability of the circulatory and respiratory systems to supply oxygen to skeletal muscles during sustained physical activity.

There are many benefits of cardio-respiratory fitness. It can reduce the risk of heart disease, lung cancer, type 2 diabetes, stroke, and other diseases.

Alarmingly, the cardio-respiratory fitness is declining globally, both for youths and adults. Preterm delivery and low birth weight are prospectively associated with low cardio-respiratory fitness. However, whether the birth weight at-term range, is associated with later CRF is largely unknown.

Scientists from the Karolinska Institute have examined this issue and conducted a prospective cohort study published in Journal of American Heart Association.

  1. The study followed more than 280,000 males from birth to military conscription at age 17-24 using Swedish population-based registers. They also included a subset of 52,000 siblings born at-term.
  2. For performing CRF test, the men were underwent a physical examination that included an evolution of their maximal aerobic performance on a bike ergo-meter .
  • The specialists found that those born with higher birth weights performed fundamentally better on the cardio-respiratory fitness test.
  • For every 450 grams of extra weight during birth, in an infant born at 40 weeks, the most extreme work limit on the bike expanded by a normal of 7.9 watts.
  • The association between birth weight and CRF fitness appears to be mainly stable across all categories of body mass index (BMI) in young adulthood and mainly driven by factors that are not shared between subset analysis of more than 52,000 siblings.
  • Birth weight may impact future cardio-respiratory health also within at-term gestational age range, highlighting the need to consider birth weight as an important factor even among gestational age term-born children.

The findings further emphasises that;

  • The importance of prevention strategies to reduce premature birth, as potential means to reduce the burden associated with low cardio-respiratory fitness.
  • Providing adequate prenatal care may be an effective means of improving an adult health.
  • Maternal nutrition and weight gain are linked with fetal weight gain and birth weight, eating a healthy diet and gaining the proper amount of weight in pregnancy are essential.

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