From the Guidelines
Elevated Hematocrit (Hct) in newborns is primarily caused by delayed cord clamping, which increases placental blood transfer and iron endowment, resulting in higher Hb and Hct levels immediately after birth 1.
Key Factors Influencing Neonatal Hct
- Delayed cord clamping (DCC): Increases total body iron content at birth by approximately 33% (~75 mg) if clamping of the umbilical cord is delayed for 2 min 1
- Gestational age: Lower gestational age is associated with lower iron stores at birth 1
- Birth weight: Low birth weight (<2500 g) is an independent risk factor for iron deficiency anemia (ID(A)) 1
- Sex: Male sex is associated with lower ferritin levels at birth compared to females 1
- Maternal iron status: Influences neonatal iron stores at birth 1
Evidence Summary
The evidence from multiple studies suggests that delayed cord clamping is associated with higher hematocrit values in newborns, with a greater effect observed in high-income countries 1. Additionally, factors such as gestational age, birth weight, sex, and maternal iron status also influence neonatal Hct levels 1.
Clinical Implications
Understanding the causes of elevated Hct in newborns is crucial for providing appropriate care and preventing potential complications. Delayed cord clamping should be considered as a factor contributing to elevated Hct levels, and other influencing factors should be taken into account when assessing newborns 1.
From the Research
Causes of Elevated Hematocrit (Hct) in Newborns
- Intra-uterine hypoxia is a cause of polycythemia in newborns, as stated in 2 and 3
- Fetal transfusion is also a related factor, as mentioned in 2
- Neonates born small for gestational age (SGA), infants of diabetic mothers (IDM), and multiple births are at risk for polycythemia, according to 3 and 4
- Placental vascular malperfusion due to asymptomatic Sars-CoV2 infection during pregnancy may cause polycythemia in the fetus as a compensatory response, as hypothesized in 5
- Early umbilical cord clamping may also be a factor, as mentioned in 4
Risk Factors
- Small for gestational age, as mentioned in 3 and 4
- Infants of diabetic mothers (IDM), as stated in 3
- Multiple births, according to 3
- Gestational age ≥34 weeks, as mentioned in 4
- Asymptomatic Sars-CoV2 infection during pregnancy, as hypothesized in 5