Neonatal Blood Pressure

What the source states (abstract, verbatim values)

• Cohort: all babies born at less than 32 weeks in the North of England in 1990–1991, daily systolic measurements in the first 10 days; 135 followed through the first year; 398 non-disabled two-year survivors with adequate data. A comparison group of 123 babies born at 32, 36 or 40 weeks.
• Systolic pressure measured by sensing arterial flow with a Doppler ultrasound probe.
• Coefficient of variation 17%, not varying with gestational or postnatal age.
• 24 weeks: initial mean 42 mm Hg, rising 20% over the first 10 days. 31 weeks: initial mean 48 mm Hg, rising 42%.
• Systolic pressure stabilised at a mean of 92 (72–112) mm Hg at a postconceptional age of 44–48 weeks, irrespective of gestation at birth.
• Systolic pressure 4–24 hours after birth was less than gestational age in weeks in only 3% of non-disabled long-term survivors.

How this page rebuilds the centiles

GA  = weeks + days/7 (birth);  PNA = postnatal age (days);  PMA = GA + PNA/7

Mean SBP
  PNA ≤ 10:  mean = D0(GA) + (D10(GA) - D0(GA)) * PNA/10
  PNA > 10:  PMA10 = GA + 10/7
             PMA ≥ 44: mean = 92
             else:      t = (PMA - PMA10) / (44 - PMA10)
                        mean = D10(GA) + (92 - D10(GA)) * t^0.6

Coefficient of variation
  PMA ≤ 34: CV = 0.17      PMA ≥ 44: CV = 20/1.96/92 = 0.111      between: linear

Centile c:   SBP_c = mean * (1 + z_c * CV)         (normal distribution)
Reading:     z = (SBP - mean) / (mean * CV);  percentile = Φ(z)

• Stated by the source: the 24 and 31 week values, the 17% CV in the first 10 days, the 92 mm Hg plateau and its 72–112 range (read as a 95% range, which gives CV 11%).
• Read from Figures 1–3 [reconstruction]: the 25–30 week means, the 32, 36 and 40 week comparison-cohort means, the straight-line rise over days 0–10 and the t^0.6 shape of the rise to the plateau. The shape was fitted to Figure 3 and reproduces three figure reads within 5 mm Hg (24–25 wk cohort at PMA 31.5: about 72; 31 wk cohort at PMA 35 and 37: about 77 and 81).
• Assumed [reconstruction]: 23 weeks extrapolated below the Figure 1 range; the CV moved linearly from 17% to 11% between 34 and 44 weeks PMA; the plateau reached at 44 weeks (the start of the stated 44–48 week window); 40+1 to 41+6 weeks use the 40-week values.
• The paper's own shortcut for its first-10-day chart is to subtract or add 35% to the mean for the 3rd and 97th centiles. A normal distribution with CV 17% puts them at mean −32% and +32%, so the shortcut is slightly wider. This page computes percentiles from the normal model and shows the shortcut values alongside during the first 10 days. After day 10 the shortcut is not shown: at the plateau it would give 60–124 mm Hg, which contradicts the stated 72–112.
• The figures were read by eye from a 1999 print; the paper publishes no centile tables. Treat values as approximate.

Use in the MIDAS trial

The MIDAS protocol (milrinone after PDA closure) cites this reference for its blood pressure thresholds: hypotension as systolic pressure below the 3rd percentile for gestational age (or mean pressure below the postmenstrual-age equivalent), hypertension as systolic pressure above the 95th percentile, and study-drug escalation above the 75th percentile. The 75th and 95th rows are shown for that reason.

References

• Northern Neonatal Nursing Initiative. Systolic blood pressure in babies of less than 32 weeks gestation in the first year of life. Arch Dis Child Fetal Neonatal Ed 1999;80(1):F38–F42. doi:10.1136/fn.80.1.F38 (PMID 10325810; PMC1720891)
• McNamara PJ, Chock VY, Rahde-Bischoff A, et al. Evaluating the efficacy and safety of milrinone for prevention of post-patent ductus arteriosus closure syndrome (the MIDAS trial) in extremely preterm infants. BMJ Open 2025;15(8):e105018. doi:10.1136/bmjopen-2025-105018