Polycythemia in Newborns (Too Many Red Blood Cells)
Medically reviewed by Dr. Michael Okonkwo, MD, FAAP · Board-Certified Neonatologist
Content reviewed against published AAP, NIH guidelines
Last reviewed:
If your baby has been diagnosed with or you suspect polycythemia in newborns (too many red blood cells), here is what the evidence says.
The short answer
Polycythemia occurs when a newborn has too many red blood cells, making the blood thicker than normal. It can cause a ruddy or deep red skin color and, in significant cases, can affect blood flow to organs. Risk factors include delayed cord clamping, maternal diabetes, and being small or large for gestational age. Most cases are mild and resolve without treatment.
Key takeaways
- Polycythemia occurs when a newborn has too many red blood cells, making the blood thicker than normal. It can cause a ruddy or deep red skin color and, in significant cases, can affect blood flow to organs. Risk factors include delayed cord clamping, maternal diabetes, and being small or large for gestational age. Most cases are mild and resolve without treatment.
- Usually normal when: Mild elevations in hematocrit without symptoms in a baby who is feeding and behaving normally
- Call your doctor if: Baby with polycythemia develops respiratory distress, seizures, or significant lethargy
- Varies by age — see the age-by-age breakdown below
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What Parents Should Know
According to AAP, NIH guidelines, polycythemia occurs when a newborn has too many red blood cells, making the blood thicker than normal. It can cause a ruddy or deep red skin color and, in significant cases, can affect blood flow to organs. Risk factors include delayed cord clamping, maternal diabetes, and being small or large for gestational age. Most cases are mild and resolve without treatment. At 0-1 month, neonatal polycythemia is defined as a venous hematocrit above 65%. Risk factors include delayed cord clamping, twin-to-twin transfusion, maternal diabetes, growth restriction, and post-maturity. Your baby may appear deeply red or ruddy-colored (plethoric). Mild polycythemia usually requires only monitoring and adequate hydration through frequent feeding. Symptoms of significant polycythemia can include jitteriness, poor feeding, lethargy, rapid breathing, and in rare cases, low blood sugar or jaundice. Severe cases may require a partial exchange transfusion to reduce blood thickness. It is generally considered normal when mild elevations in hematocrit without symptoms in a baby who is feeding and behaving normally. However, you should contact your pediatrician promptly if baby with polycythemia develops respiratory distress, seizures, or significant lethargy.
Normal vs. Concerning
By Age
What to expect by age
0-1 month
Neonatal polycythemia is defined as a venous hematocrit above 65%. Risk factors include delayed cord clamping, twin-to-twin transfusion, maternal diabetes, growth restriction, and post-maturity. Your baby may appear deeply red or ruddy-colored (plethoric). Mild polycythemia usually requires only monitoring and adequate hydration through frequent feeding. Symptoms of significant polycythemia can include jitteriness, poor feeding, lethargy, rapid breathing, and in rare cases, low blood sugar or jaundice. Severe cases may require a partial exchange transfusion to reduce blood thickness.
1-3 months
Polycythemia typically resolves in the first few days to weeks as red blood cell levels normalize. As excess red blood cells are broken down, jaundice may develop. Your pediatrician will monitor bilirubin levels if needed. After resolution, there are generally no ongoing effects.
3-6 months
Polycythemia should be fully resolved. There are no lasting effects from mild to moderate neonatal polycythemia in most cases. Development should proceed normally.
6-12 months
No ongoing concerns related to neonatal polycythemia. Your baby should be developing normally.
What to Tell Your Pediatrician
- Describe when you first noticed polycythemia in newborns (too many red blood cells) and how it has changed over time.
- Note your baby's current age and which age-specific patterns you are seeing.
- Mention if your baby appears very red or deeply flushed.
- Mention if you notice jitteriness, poor feeding, or unusual sleepiness in a baby with known polycythemia.
- Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
- Bring a list of any questions or observations you want to discuss at the appointment.
What Should You Do?
When to take action
- Mild elevations in hematocrit without symptoms in a baby who is feeding and behaving normally
- A ruddy or red appearance in the first day or two that gradually normalizes
- Polycythemia that resolves with adequate feeding and hydration
- Your baby appears very red or deeply flushed
- You notice jitteriness, poor feeding, or unusual sleepiness in a baby with known polycythemia
- Your baby had risk factors for polycythemia and you want to ensure appropriate monitoring
- Baby with polycythemia develops respiratory distress, seizures, or significant lethargy
- Signs of low blood sugar (jitteriness, tremors, poor feeding) in a baby with known or suspected polycythemia
What You Can Do at Home
- Keep track of when you notice polycythemia in newborns (too many red blood cells) — noting the time of day, duration, and any triggers can help your pediatrician.
- Remember that mild elevations in hematocrit without symptoms in a baby who is feeding and behaving normally — this is generally within the range of normal.
- At 0-1 month, focus on observation rather than intervention unless your pediatrician advises otherwise.
- Follow any care instructions from your pediatrician. Keep a written log of symptoms to bring to appointments.
- While monitoring at home, seek immediate care if baby with polycythemia develops respiratory distress, seizures, or significant lethargy.
Related Conditions
Anemia in Newborns
Anemia in newborns means the baby has fewer red blood cells or lower hemoglobin than normal. Causes include blood type incompatibility, blood loss, prematurity, and infections. Mild physiologic anemia is normal around 6-8 weeks as birth red blood cells are replaced. Signs of significant anemia include pallor, lethargy, poor feeding, and rapid breathing.
ABO Blood Type Incompatibility in Newborns
ABO incompatibility occurs when a mother and baby have different blood types (most commonly a type O mother with a type A or B baby), causing the mother's antibodies to attack the baby's red blood cells. This can lead to more severe jaundice and anemia in the newborn. It is manageable with monitoring and treatment, and the vast majority of babies do well.
Newborn Low Blood Sugar (Hypoglycemia)
Neonatal hypoglycemia (low blood sugar) is common in the first hours and days of life, especially in babies who are large or small for gestational age, premature, born to mothers with diabetes, or stressed during delivery. Mild hypoglycemia often responds to frequent feeding. More significant or persistent hypoglycemia may require IV glucose treatment. Early and frequent feeding is the best prevention.
Related Resources
Frequently asked questions
Is polycythemia in newborns (too many red blood cells) normal?
When should I call the doctor about polycythemia in newborns (too many red blood cells)?
When is polycythemia in newborns (too many red blood cells) normal?
What causes polycythemia in newborns (too many red blood cells)?
What should I mention to my pediatrician about polycythemia in newborns (too many red blood cells)?
Is polycythemia in newborns (too many red blood cells) normal at 0-1 month?
Is polycythemia in newborns (too many red blood cells) normal at 1-3 months?
Should I go to the ER for polycythemia in newborns (too many red blood cells)?
Does polycythemia in newborns (too many red blood cells) go away on its own?
References
Doctor Visit Checklist
Bring this checklist to your next pediatrician visit to discuss Polycythemia in Newborns (Too Many Red Blood Cells).
Things to mention
- Describe when you first noticed polycythemia in newborns (too many red blood cells) and how it has changed over time.
- Note your baby's current age and which age-specific patterns you are seeing.
- Mention if your baby appears very red or deeply flushed.
- Mention if you notice jitteriness, poor feeding, or unusual sleepiness in a baby with known polycythemia.
- Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
- Bring a list of any questions or observations you want to discuss at the appointment.
Observations to share
- Your baby appears very red or deeply flushed
- You notice jitteriness, poor feeding, or unusual sleepiness in a baby with known polycythemia
- Your baby had risk factors for polycythemia and you want to ensure appropriate monitoring
Urgent signs to report immediately
- Baby with polycythemia develops respiratory distress, seizures, or significant lethargy
- Signs of low blood sugar (jitteriness, tremors, poor feeding) in a baby with known or suspected polycythemia
My notes
From ismybabyalright.com — free, evidence-based baby health guides
All content follows our editorial policy and is reviewed against published clinical guidelines.
2,705 evidence-based guides6 authoritative medical sources5 medical advisory board members
Related Resources
Bottom line
Most cases of polycythemia in newborns (too many red blood cells) are normal. Talk to your pediatrician if baby with polycythemia develops respiratory distress, seizures, or significant lethargy.
Trust your instincts. If something feels wrong, reach out to your pediatrician. Worrying about your baby means you care — that is a good thing.
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Related Medical Concerns
Anemia in Newborns
Anemia in newborns means the baby has fewer red blood cells or lower hemoglobin than normal. Causes include blood type incompatibility, blood loss, prematurity, and infections. Mild physiologic anemia is normal around 6-8 weeks as birth red blood cells are replaced. Signs of significant anemia include pallor, lethargy, poor feeding, and rapid breathing.
ABO Blood Type Incompatibility in Newborns
ABO incompatibility occurs when a mother and baby have different blood types (most commonly a type O mother with a type A or B baby), causing the mother's antibodies to attack the baby's red blood cells. This can lead to more severe jaundice and anemia in the newborn. It is manageable with monitoring and treatment, and the vast majority of babies do well.
Newborn Low Blood Sugar (Hypoglycemia)
Neonatal hypoglycemia (low blood sugar) is common in the first hours and days of life, especially in babies who are large or small for gestational age, premature, born to mothers with diabetes, or stressed during delivery. Mild hypoglycemia often responds to frequent feeding. More significant or persistent hypoglycemia may require IV glucose treatment. Early and frequent feeding is the best prevention.
My Baby's Head Shape Looks Abnormal
Many babies develop temporary head shape irregularities that are completely normal. A cone-shaped head from vaginal delivery reshapes within days. Mild positional flattening (plagiocephaly) from sleeping on the back is very common and usually improves with repositioning and tummy time. However, head shape changes involving ridges, a persistently bulging fontanelle, or rapid head growth changes should be evaluated to rule out craniosynostosis.
Achondroplasia (Dwarfism) in Babies
Achondroplasia is the most common form of short-limbed dwarfism, affecting about 1 in 15,000 to 40,000 births. It is caused by a mutation in the FGFR3 gene and is usually apparent at birth with characteristic features including short limbs, a larger head, and a prominent forehead. Intelligence is normal. With monitoring for specific complications and supportive care, children with achondroplasia lead full, active, and independent lives.
Adenoid Hypertrophy and Breathing
Adenoids are lymphoid tissue located behind the nose that help fight infection in young children. When adenoids become enlarged (adenoid hypertrophy), they can block the nasal airway, causing chronic mouth breathing, snoring, nasal speech, and sleep-disordered breathing. Enlarged adenoids are most common between ages 2-7 and are a leading cause of obstructive sleep apnea in young children. Treatment ranges from watchful waiting and nasal steroids to surgical removal (adenoidectomy) if breathing or sleep is significantly affected.