Another important development was the blood pressure standards published in 1987 in the Second Task Force Report. These were based on data from nearly 13,000 newborns and infants and presented centile values of blood pressure according to gestational age, sex and birth weight. Based on these data, hypertension (nt) was diagnosed when systolic blood pressure values were found to be above the 95th centile for a given age, sex and birth weight. Also of great importance were the results provided by Zubrow, who prospectively assessed blood pressure using the oscillometric method in 695 children admitted to the OIRN in the first three months of life. At that time, mean arterial pressure was assessed and the relationship of blood pressure height to gestational age, birth weight and corrected age was demonstrated. Based on these data, a 95% confidence interval was determined for the normal values for a given calendar age, corrected age and body weight.

The most objective data on blood pressure heights in the earliest period of life, while based on a non-invasive oscillometric method, were provided by Kent et al. These included both neonates born at term and babies born between 28 and 36 weeks' gestation. In this study, the authors also observed the 'catch-up' phenomenon, also described by other authors. The advantage of these norms compared to the Zubrow norms was that only healthy newborns and preterm infants not requiring intensive treatment were measured. In addition to the homogeneity of the group, there was an additional advantage in defining systolic, diastolic and mean arterial pressure norms according to gestational age and birth weight in the first month of life. Previous data on blood pressure in preterm infants were mainly based on results from smaller and less homogeneous patient groups, as well as often involving other, more invasive measurement methods. It should be mentioned that, in addition to Kent et al. the oscillometric method in children born prematurely was also used by Georgieff et al. In a study by Pejović et al. blood pressure was measured using the oscillometric method in 373 newborns, more than 70% of whom had very low birth weight and were born before 32 weeks of gestation. All babies were assessed as haemodynamically stable. The authors showed that blood pressure on the first day of life correlated with gestational age and birth weight. The correlation between birth weight and gestational age appears to be weaker in healthy and term newborns. Another study by Kent et al. assessing blood pressure in more than 400 healthy and term newborns showed no relationship between birth weight, body length and gestational age and blood pressure.
As mentioned above, during the first month of life there is a gradual adaptation of the cardiovascular system expressed, among other things, by an increase in blood pressure. An important physiological issue is to determine when a neonate born prematurely reaches the blood pressure values typical of a full-term neonate. This phenomenon called 'catch-up' was described in the Northern Neonatal Nursing Initiative study. This study, based on manometric, oscillometric and Doppler BP measurements, developed BP norms based on 3rd, 50th and 97th percentile values for babies born before 32 weeks gestation. It was also observed that preterm infants reach ('catch up') blood pressure values corresponding to those found in full-term infants around day 14 after birth. The increase in SBP and DBP values is 2.3-2.7 and 1.6 - 2.0 mm/Hg/day for the first 5 days of life, respectively. After this period, the rate of increase in SBP decreases to 0.25 mmHg/day and DBP to 0.15 mmHg/day. The study by Kent et al. shows that the rate of rise in blood pressure after birth is inversely proportional to the gestational age of the preterm infant. It is also shorter, lasting about a week in babies born after 32 weeks gestation, and longer and faster, lasting up to 2-3 weeks of life in babies born before 32 weeks gestation.

In neonates born at term, differences in BP are related to intrauterine nutritional status. In neonates born on time and with adequate weight for gestational age, blood pressure rises in the first two days after birth and then stabilises. In contrast, neonates with features of intrauterine dystrophy show lower blood pressure values after birth compared to normally nourished neonates, followed by a rapid increase in blood pressure values, which by the end of the first month of life reach the same values as in neonates born with normal body weight.