What Is a Micro Preemie?

Definition of a Micro Preemie

A micro preemie in the hospital.
A micro preemie in the hospital.. Blend Images - ERproductions Ltd/Getty Images

The term micro preemie usually refers to a premature baby who is either less than 800 grams (1 pound 12 ounces) or younger than 26 weeks at birth. However, depending on the circumstances, a baby under 3 pounds (1500 grams) or born at less than 29 weeks gestation may be classified as a micro preemie.

The number of micro preemies born each year is relatively small, but the 50,000 micro-preemies born yearly in the United States have very high medical care needs.

Survival can range from 10 percent to 80 percent. However, many more micro preemies are surviving today than ever before due to advances in medical knowledge and technology that can care for them.

Survival rates of micro preemies are reported based on gestational age, although no two cases are alike:

  • 22 weeks gestation: About 10% of infants survive
  • 23 weeks gestation: About 1/2 of infants survive
  • 24 weeks gestation: About 2/3 of infants survive
  • 25 weeks gestation: About 3/4 of infants survive

Micro Preemie Health Problems

Micro preemies face a number of health problems that are addressed in the neonatal intensive care unit (NICU). Generally, the earlier a baby is born, the higher the risk of complications and the longer they will stay in the NICU. Some health complications micro preemies face include:

  • Hyperbilirubinemia: High levels of bilirubin, a compound resulting from the natural breakdown of blood, causing jaundice. Jaundice can cause brain damage if not treated effectively through the use of special lights that help the body eliminate bilirubin.
  • Apnea: Pauses in breathing that cause decreases in heart rate.
  • Anemia: A lower than normal number of red blood cells, which are needed to carry oxygen to the body.
  • Low Blood Pressure: A common complication that may be due to infection, blood loss, fluid loss, or medications administered before delivery.
  • Respiratory Distress Syndrome: Difficulty breathing due to immature lungs that don't produce enough surfactant, a substance that allows the lungs to expand properly.
  • Bronchopulmonary Dysplasia: A common lung problem among premature infants, especially micro preemies, is often successfully treated with medication and oxygen.
  • Infection: All premature infants, and especially micro preemies, are immunocompromised, meaning they are less able to fight off germs that can cause serious illness.
  • Patent Ductus Arteriosus: In micro preemies, the ductus arteriosus (a short blood vessel connecting the main blood vessel supplying the lungs to the aorta) frequently stays open in premature babies. Due to this abnormal opening, excess blood can flow into the lungs, causing breathing difficulties and in some cases heart failure.
  • Retinopathy of Prematurity: Abnormal growth of the blood vessels in an infant's eye can cause damage ranging from mild to severe (blindness).

Although all micro preemies are very underdeveloped at birth and require constant medical care, many grow up with no long term effects of prematurity.

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