POSTNATAL DEVELOPMENT OF RENAL HYDROGEN ION EXCRETION CAPACITY IN RELATION TO AGE AND PROTEIN INTAKE

ABSTRACT. Svenningsen, N. W. and Lindquist, B. (Department of Paediatrics, University Hospital, Lund, Sweden). Postnatal development of renal hydrogen ion excretion capacity in relation to age and protein intake. Acta Paediatr Scand, 63: 721, 1974.—The cumulative and maximum renal hydrogen ion excretion capacity after induced acidosis has been studied in six term and twenty preterm infants at 1–3 and 44 weeks of postnatal age corresponding to for preterm babies 34–36 and 37–39 and for term babies 41–43 and 44–46 weeks of gestational age. The maximum net hydrogen ion (H⁺_NAE) excretion capacity is lower in preterm than in term infants at 1–3 weeks of postnatal life. However, when approaching full gestation there is a considerable increase of the H+_NAE excretion capacity of pretem infants almost equal to that found in term infants at 1–3 weeks of age. High dietary protein intake lasting for in average two to three weeks in preterm infants does not change the maximum renal H⁺ excretion during induced acidosis, but significantly enhances the initial increment of excretion rate of titratable acid (H⁺_TA) in comparison to preterm infants fed low protein diets. The findings of the present investigation suggest that the development of renal hydrogen ion excretion capacity in preterm infants during the first weeks of life is related primarily to gestational age. This development may, however, to a certain degree respond to increased excretory needs imposed by dietary load.     

The postnatal hypotransferrinemia of early preterm newborn infants.

Preterm newborns were found to be markedly hypotransferrinemic when compared with normal term infants. At birth the concentration of transferrin in sera from preterm infants of gestational age equal to or less than 32 weeks is 45% of that found in normal term infant sera. The preterm infant transferrin levels slowly rise so that 7-8 weeks after birth they are 78% of the level found in the sera of normal term infants. We also found that the serum transferrin concentrations at birth correlate with gestational age. Therefore, the transferrin levels postnatally in early preterm infants reflect postconceptional rather than postnatal age.     

Thyroid function in 76 sick preterm infants 30-36 weeks: results from a longitudinal study

AIM: To assess thyroid function in 76 sick preterm infants 30-36 weeks gestational age. PATIENTS AND METHODS: Measurement of serum TSH, T4, T3, free T4 and rT3 in the mother and cord at delivery, and in the infant at 1 and 24 hours, 1 and 3 weeks, 2, 4, 6 and 12 months of postnatal age. These values were compared with those of 75 healthy age-matched controls. Gestational age was 30 weeks in 24, 31 weeks in 23, 32 weeks in 13, 33 weeks in 13, 34 weeks in one, 35 weeks in one and 36 weeks in one. Hypothyroxinemia at each postnatal age was defined as serum free T4 values under -2 SD of the mean of controls. RESULTS: Forty-four patients were normothy-roxinemic at all times, and 32 presented hypothyroxinemia at 24 hours (29 patients), 1 week (seven patients) and 3 weeks (two patients). Follow-up of 31 patients who were normothyroxinemic at 24 hours of life showed that at one week three (9.7%) were hypothyroxinemic and at 3 weeks all were normothyroxinemic. At 24 hours of life, all patients with patent ductus arteriosus and all patients treated with dopamine were in the hypothyroxinemic range. CONCLUSION: Hypothyroxinemia may be present in sick preterm infants 30-36 weeks of gestational age, particularly in those treated with dopamine and/or presenting patent ductus arteriosus.     

Lung function and the Hering Breuer reflex in the neonatal period.

Lung function and the occurrence of the Hering Breuer reflex during the neonatal period has been investigated. To assess the effect of extrauterine and intrauterine maturation on the strength of the reflex both preterm and term infants were recruited. Ten preterm infants, born at a median gestational age of 29.5 weeks (range 27-34) were studied serially over the first four weeks of life and 10 term infants were studied at a median postnatal age of 1.5 days (1-4). All of the infants were recruited from the neonatal unit and initially had had some form of respiratory distress. Respiratory rate, tidal volume and compliance were measured and end inspiratory occlusion performed in an attempt to provoke the Hering Breuer reflex. The Hering Breuer reflex was provoked in all infants on all occasions. There was no difference in the strength of the reflex between the preterm and term infants or preterm infants studied at different postnatal ages. All infants studied regardless of maturity or postnatal age had non-compliant lungs and a rapid respiratory rate. These data suggest a lack of intrauterine and extrauterine maturation of the Hering Breuer reflex in the neonatal period amongst infants with non-compliant lungs.     

Longitudinal measurements of bone status in preterm infants

BACKGROUND: Quantitative ultrasound measurement of the speed of sound (SOS) through bone has been investigated as a means of assessing bone status in preterm infants. Few studies report longitudinal measurements. OBJECTIVE: To assess longitudinal changes in bone SOS in preterm infants. METHODS: Sixty preterm infants with gestational ages of < 33 weeks and with birth weight appropriate for gestational age (AGA), and 48 healthy, term AGA infants were enrolled. SOS measurements of the tibia were made within the first week of life in the preterm infants, and within the first 72 hours of life in the term infants. During their hospital stay, weekly measurements of tibial SOS were made in 29 of the preterm infants, who were divided into three gestational age groups: Group 1: 24-26 weeks (n = 8), Group 2: 27-29 weeks (n = 9), and Group 3: 30-32 weeks (n = 12). RESULTS: The median SOS value for the 60 newborn preterm infants was significantly lower than that for the 48 newborn term infants (2,924 versus 3,036 m/sec, p < 0.001). At each time point, SOS values for each of the preterm infant gestational age groups were significantly lower than the term newborn infant SOS values. SOS values decreased significantly over time for the entire cohort of 29 preterm infants (p < 0.001), and for Groups 1 (p = 0.015) and 2 (p = 0.003). At several time points, there was a significant negative correlation between serum alkaline phosphatase levels and SOS values, and a significant positive correlation between serum phosphorus levels and SOS values. CONCLUSION: SOS measurements of the tibia decline during hospitalization in preterm infants, suggesting a progressive loss of bone strength. Longitudinal measurements of bone SOS in combination with serum alkaline phosphatase and serum phosphorus levels may identify infants at risk of developing osteopenia of prematurity.     

Cord blood and postnatal serum leptin and its relationship to steroid use and growth in sick preterm infants

OBJECTIVE: To study the effect of prenatal and postnatal glucocorticoids use on serum leptin and weight gain in sick preterm infants and its correlation with caloric intake. METHODS: Serum leptin was measured in 24 neonates at day 1 (cord), 14 and 28 by radioimmunoassay. Total caloric intake (enteral and parenteral) and weight were measured on days 14 and 28 of life. RESULTS: Mean birth weight and gestational age of study infants were 864 +/- 273 g (mean +/- SD) (range 520-1755 g), and 26.6 +/- 2.4 weeks (23-32 weeks) respectively. Cord blood leptin was greater in infants whose mothers received antenatal steroids (1.98 +/- 1.05 ng/ml vs 0.94 +/- 0.39 ng/ml, p=0.004). Serum leptin increased postnatally from 1.52 +/- 1.0 ng/ml at birth to 2.2 +/- 1.3 ng/ml on day 28 of life (p=0.03). Mean serum leptin had an inverse exponential relationship with postnatal weight gain by day 28 of life (R2=0.56). Total caloric intake on days 14 and 28 of life did not correlate with postnatal weight gain. CONCLUSIONS: Increased serum concentration of leptin following glucocorticoids may be associated with poor weight gain in sick preterm infants.     

Constitutive IL-10 expression by lung inflammatory cells and risk for bronchopulmonary dysplasia

Expression of IL-10 is decreased in lungs of preterm infants. We determined the constitutive and lipopolysaccharide (LPS)-induced IL-10 synthesis by lung inflammatory cells from preterm and term infants and examined their relationship to gestational age and/or incidence of bronchopulmonary dysplasia (BPD). A total of 37 infants; preterm neonates at gestational ages of 23-27 wk (group 1); 28-34 wk (group 2), and four full-term infants with meconium aspiration (group 3) were enrolled. One sample of lung inflammatory cells, obtained during postnatal d 1-3, and another during postnatal d 4-7 were cultured in vitro in presence or absence of 100 mug/mL of LPS. Secreted IL-10 was measured by ELISA. A positive relationship was found between gestational age and LPS-induced, but not constitutive IL-10 production within 1-3 d of life; group 1 on d 1-3 had a significant number of IL-10 nonresponders compared with group 2. All term neonates in group 3 had positive LPS-induced IL-10 response. Thus, in utero maturation of IL-10 gene expression is due to acquisition of inducibility. In contrast, constitutive IL-10 production within d 1-3 of life correlated with, and predicted the incidence of BPD in the highly vulnerable very premature infants.     

Respiratory syncytial virus (RSV) outbreak in the NICU: description of eight cases

Respiratory syncytial virus (RSV) has been recognized as a major nosocomial hazard on pediatric wards. Because of maternally acquired antibodies, symptomatic RSV infection is rare in term neonates. During an outbreak of RSV in our neonatal ICU, 12 infants (gestational age = 34 +/- 5 weeks) remained RSV negative. In contrast, eight preterm infants (gestational age = 28 +/- 2 weeks) became RSV positive. Four infants became very sick with RSV and required mechanical ventilation and support. Acute respiratory distress syndrome (ARDS) developed in two of them resulting in death of one of them. Control measures were effective in controlling the outbreak. We conclude that during an RSV outbreak in the neonatal ICU, the attack rate is higher in preterm infants born at lower gestational age resulting in significant mortality and morbidity.     

Thyroid function in preterm infants 27-29 weeks of gestational age during the first four months of life: results from a prospective study comprising 80 preterm infants

AIM: Assessment of thyroid function in preterm neonates (PTN) 27-29 weeks of gestational age. PATIENTS AND METHODS: 80 PTN, gestational age 27 weeks in 24, 28 weeks in 28, and 29 weeks in 28. Neonates were classified as healthy (n=17) or sick (n=63). Measurement of serum TSH, free T4, T4, T3 and rT3 in the mother and in the cord at the time of delivery, and in the infant at 1 hour, 24 hours, 1 week, 3 weeks, and 2 and 4 months of postnatal age. RESULTS: In healthy and sick preterms, TSH values peaked at 1 hour and decreased thereafter. Healthy PTN presented a peak in free T4 values at 24 hours that was not observed in sick neonates. Sick PTN had a lower TSH peak and lower free T4 values at 24 hours and 1 week than healthy ones (p < 0.05). Healthy PTN 27-29 weeks had lower TSH peak at 1 hour and lower free T4, T3 and T4 values during the first 2 months than healthy PTN 30-35 weeks (PTN30-35w) previously evaluated (p < 0.05). However, at all postnatal times healthy preterms had free T4 values above -2 SD of the mean values of healthy PTN30-35w. A wide range of free T4 values was observed in the sick group. Free T4 values above -2 SD of the mean values of healthy PTN30-35w were detected in a high proportion of sick PTN (58.3% at 24 hours, 73.5% at 1 week, 93.9% at 3 weeks, 85.1% at 2 months and 100% at 4 months). CONCLUSIONS: Prematurity and disease influence thyroid function, and consequently thyroid function should be individually assessed in preterms 27-29 weeks of gestation during the first 2 months of life.     

Behavioural response to pain in healthy neonates.

A bedside technique for evaluating the behavioural response of healthy neonates to pain was assessed. Thirty six term infants (median gestational age 40 weeks; median postnatal age 4 days) and 31 preterm infants (median gestational age 34 weeks; median postnatal age 4 days) were assessed at the cotside for their response to heel preparation and heel lance for routine blood sampling. The facial actions of brow bulge, eye squeeze, nasolabial furrow, and open mouth were noted, and also the presence or absence of crying. Thirty five (97%) term and 26 (84%) preterm infants showed an increase in the number of behaviours in response to heel lance. Brow bulge and nasolabial furrow were seen most often, and occurred more often than crying in the two groups. There was good interobserver agreement (94%). The consistency of response and the high degree of interobserver agreement makes this method of behavioural assessment of acute pain of use in healthy neonates.     

Postnatal overestimation of gestational age in preterm infants

In a study involving 25 preterm infants, obstetric clinical age (standard gestational age) was determined by history, physical examination, and ultrasonographic evaluation. Postnatally, these infants were then evaluated using the Dubowitz Scoring System (DSS) for gestational age assessment. The DSS, as administered by us, significantly overestimated gestational age compared with the standard gestational age (mean +/- 1 SD: 34.2 +/- 2.9 vs 32.5 +/- 3.9 weeks, respectively) in preterm infants. To illustrate, the gestational ages of 13 newborns (52%) in the total study group were each overestimated by more than two weeks. This percentage increased to 75% among the 16 infants whose gestational ages were less than 34 weeks (by standard gestational age). When the standard gestational age was underestimated by the DSS, this difference never exceeded two weeks. These findings suggest that the present system of postnatal assessment of gestational age in preterm infants needs further investigation.     

Free-radical-induced lipid peroxidation during the early neonatal period

The effect of gestational age on postnatal free-radical-mediated lipid peroxidation was studied in 19 term (gestational age 37–42 weeks) and 21 healthy preterm (gestational age 31–36 weeks) infants by measurement of expired ethane and pentane during the first 7 days of life. Ethane (11.9 versus 5.7 pmol/kg/min; p = 0.0001) and pentane (11.4 versus 7.5 pmol/kg/min; p = 0.01) were significantly higher in preterm than in term infants. Correlations were found between gestational age and ethane ( r = 0.60, p = 0.0001) for days 1–7 and pentane ( r = 0.54, p = 0.0003) for days 3–7; and between birth weight and ethane ( r = 0.58, p = 0.0001) and pentane (r = 0.55, p = 0.0003). These results indicate that during the postnatal period, immaturity is a major factor determining the rate of free-radial-mediated lipid peroxidation.     

Pharmacokinetics of single dose intravenous propacetamol in neonates: effect of gestational age

AIM: To investigate the pharmacokinetics and pharmacodynamics of single dose propacetamol in preterm and term infants on the first day of life. METHODS: Neonates were stratified by gestational age. Preterm (< 37 weeks) and term (37-41 weeks) infants received a single dose of propacetamol in the first 24 hours of life when they had minor, painful procedures or as additional treatment in infants receiving opioids. Blood samples were taken from an arterial line, and pain was evaluated by a multidimensional pain scale. Results were reported as mean (SD). Student's t and Wilcoxon tests were used to compare the groups. RESULTS: Thirty neonates were included, 10 of which were term infants. Serum half life was 277 (143) minutes in the preterm infants and 172 (59) minutes in the term infants (p < 0.05). Clearance was 0.116 (0.08) litre/kg/h in the preterm infants and 0.170 (0.06) litre/kg/h in the term infants (p < 0.05). Gestational age correlated with serum half life (r = -0.46). No effect of sex or administration of prenatal steroids was found on the pharmacokinetics of paracetamol. In neonates who only received propacetamol (n = 15), the level of analgesia seemed to be associated with the therapeutic (> 5 mg/l) level. CONCLUSIONS: A correlation was found between gestational age and the serum half life of propacetamol. The maturational trend of clearance and half life in preterm and term neonates is in line with data on the pharmacokinetics of propacetamol beyond the newborn period.     

Myocardial function in term and preterm infants. Influence of heart size,gestational age and postnatal maturation

Background

Sparse knowledge exists on the differences in cardiac function between term and preterm infants. This study examines the impact of heart size, gestational age and postnatal maturation on myocardial function.

Aim

To assess and compare serial echocardiographic indices of myocardial function in term and moderately preterm infants.

Methods

Longitudinal, prospective, observational echocardiographic cohort study of 45 healthy term infants examined at day three and at 12–20 weeks postnatal age and 53 moderately preterm infants (gestational age 31–35 weeks) examined at day three and at term equivalent (4–10 weeks postnatal age).

Outcomes

Primary: Systolic mitral and tricuspid annular plane excursions and annular peak systolic pulsed wave tissue Doppler (pwTDI) velocities.Secondary: Indices normalized for heart size.

Results

On day three, all indices were higher in the term than in the preterm infants whereas normalized systolic pwTDI velocities were lower in the term infants and normalized excursions showed no difference. All indices increased with advanced postnatal age. The indices in term infants on day three were lower than in preterm infants at term equivalent, with and without normalization. After postnatal maturation in both groups, all indices were higher in the term group (except left pwTDI), whereas normalized indices showed no consistent pattern.

Conclusions

Myocardial function indices increased with gestational age at birth and more profoundly with postnatal maturation. Serial examinations of non-normalized and normalized myocardial function indices showed no sustained differences between the preterm and the term infants.Normalization by heart size may be of value when assessing myocardial function in infants.     

Value of brain ultrasound studies of newborn infants for prediction of neurological development in the 1st year of life

BACKGROUND: Recent advances in perinatology have been associated with a decrease in perinatal mortality. However, nowadays detailed assessments are of major importance for accurate prediction of neurologic development of extreme low birth weight infants and term infants with severely disturbed postnatal adaptation. This study examined the role of cranial ultrasound for the prediction of developmental progress during the first year of life. PATIENTS AND METHODS: Fifty nine infants with gestational age less than 33. weeks and fifty seven infants with gestational age above 32. weeks were studied. Each infant was classified as normal, suspect or abnormal using cranial ultrasound and a specialized scoring system during the first days and twelve month of life. Repeated structured neurological examination were carried out during the first year of corrected age. By statistical analysis was investigated the correlation between the degree of ultrasound abnormalities and neurological outcome of neonates of both different gestational age groups. RESULTS: We diagnosed the same share of pathological ultrasound scans in both groups within the first days of life. In contrast there were remarkable differences concerning the results of sonographic investigation at the end of the first year of life. We demonstrated a significant higher incidence of abnormal findings in neonates with a gestational age less than 33 weeks at this point of time. The neurological progress of neonates of both groups was significantly disturbed in cases of major sonographic abnormalities. Cases of mild or moderate ultrasound abnormalities were significantly associated with a poor neurologic outcome only in neonates with a gestational age less than 33 weeks. By statistical analysis we proved a significant value of cranial ultrasound for prediction of neurological development of preterm neonates with gestational age less than 33 weeks. The certainty prediction of neurodevelopmental sequelae in neonates with gestational age above 32 weeks was associated with major sonographic abnormalities but not with mild or moderate sonographic pathology. CONCLUSION: The prognostic accuracy of ultrasound scans performed in the first week of life is important for preterm neonates with gestational age less than 33 weeks. In neonates with gestational age above 32 weeks we revealed no significant predictive value of the method. This limits the value of this technique in this patients as a reliable method for recognising of the infants with the need of early rehabilitation.     

Nitric oxide levels in preterm and term infants and in premature infants with bacteremia

OBJECTIVE: To determine the serum nitric oxide levels in healthy neonates and in infants with bacteremia. METHODS: We performed a prospective study in a tertiary neonatal intensive care unit. The serum nitric oxide levels were measured in all infants at birth (basal) and in the infected neonates also on the first 2 days of bacteremia. RESULTS: Thirty-three neonates (10 term, 23 preterm) were included. Eleven preterm infants (mean gestational age 27 weeks) had bacteremia. The main blood culture isolates included coagulase-negative staphylococci (n=4), Klebsiella pneumoniae (n=3), and Escherichia coli (n=3). The serum nitric oxide levels increased during infection in 10 infants (p <0.008). The mean nitric oxide level before infection was 44 microM and during infection 96 microM (p=0.008). In the healthy babies, the mean nitric oxide level was 26 microM in those with a gestational age <27 weeks, 44 microM in those born between 28 and 36 weeks of gestation, and 63 microM in term infants. CONCLUSIONS: Bacteremic preterm infants produce significantly higher amounts of nitric oxide. The basal nitric oxide levels at birth may be correlated with gestational age.     

Urinary cyclic AMP in infants admitted to a neonatal intensive care unit.

The urinary excretion of cyclic AMP was studied during the first 3 days of life in 46 randomly selected infants admitted to a neonatal intensive care unit. The data were compared with those of normal newborn infants. Urinary cyclic AMP concentrations were significantly correlated with gestational age (all patients), and with birth weight (all patients except infants of diabetic mothers (IDMs)). The urinary cyclic AMP/creatine ratio increased from day 1 to day 3 in normal newborns and in IDMs, and tended to increase also in small-for-gestational age (SGA), low birth weight (LBW), and sick, term infants, although the changes in the latter groups were not statistically significant. Four infants studied with parallel determinations showed increased cyclic AMP/creatinine ratio from day 1 to day 3 both in plasma and urine. All urinary cyclic AMP/creatine ratios were lower than the corresponding ratios found in plasma. In LBW infants, there was an inverse relationship between urinary cyclic AMP and serum calcium. In IDMs a positive correlation was observed between urinary cyclic AMP and blood glucose concentration. In conclusion, the excretion of cyclic AMP in sick newborn infants is influenced by the following factors: gestational age, postnatal age, birth weight, and derangements of serum calcium and blood glucose concentrations.     

Erythrocyte insulin binding in preterm newborn infants

To characterize the erythrocyte insulin receptor in newborn infants we studied the binding of 125I-insulin to the erythrocytes from 42 preterm infants (14 at birth, 14 aged 2-7 days, and 14 aged 8-16 days) with a mean gestational age of 34.1 wk, and from 32 term infants (16 at birth and 16 aged 2-7 days). The insulin binding to cord blood erythrocytes from preterm infants was significantly higher than that of cord blood cells from term infants and to postnatal cells from preterm as well as term infants. The erythrocytes from preterm infants aged 2-7 days bound more insulin than cells from preterm infants aged 8-16 days. The maximum insulin binding (specific insulin binding at tracer concentration of insulin) correlated negatively with the gestational age both at birth and over the 1st postnatal wk. In the preterm infants there was a strong negative correlation between the maximum insulin binding and postnatal age. The enhanced insulin binding to cord blood erythrocytes from preterm infants was due to both an increased receptor concentration and a high affinity for insulin. The increased affinity persisted over the 1st wk of life. In preterm infants older than 1 wk the insulin binding characteristics were basically similar to those in term newborn infants. In all infants studied the receptor concentration seemed to be postnatal age dependent while the receptor affinity was gestational age dependent. No correlation was found between the insulin binding data and the plasma concentrations of immunoreactive insulin or C-peptide.(ABSTRACT TRUNCATED AT 250 WORDS)     

Postnatal Development of Renal Function in Very Low Birth weight Infants

ABSTRACT. The postnatal development of renal function was compared in infants with a gestational age of 25–30 weeks, mean 27.8 weeks (GA 28), and in infants with a gestational age of 31–34 weeks, mean 32.5 weeks (GA 32). The infants were comparable with regard to postnatal course, fluid, caloric and salt intake. Observations were made during the 1st, 2nd and 4th-7th (mean 5th) postnatal weeks. From the 1st to the 5th postnatal week the creatinine clearance (C_Cr ml/min/1.73 m²), increased from 11 to 20 in GA 28 and from 15 to 30 in GA 32. At 2 weeks of age C_Cr was significantly lower in GA 28 than in GA 32. During the first week of life diuresis was lower in GA 28 than in GA 32 but thereafter was the same in both groups. We interpret this as a sign of dehydration in GA 28. Serum arginine vasopressin (S-AVP) concentrations were high in both groups at all ages. Mean urine osmolality was low (<300) regardless of postnatal age and S-AVP. Urinary sodium excretion was high at 1 week of age in both groups and decreased with increasing postnatal age. Na excretion was slightly higher in GA 28 than in GA 32 at 1 but not at 2 and 5 weeks. UK/UNa was below 1 in both groups during the first week of life and increased with postnatal age. Urinary aldosterone excretion was high in both GA 28 and GA 32 at all ages. Serum sodium levels were lower in GA 28 than in GA 32 at all ages. Hyponatremia was observed in 13/32 infants in GA 28 and in 1/45 infants in GA 32. We conclude that the postnatal development of renal function is retarded in all preterm infants and is slightly slower in infants with a GA below 31 weeks than in infants with a GA of 31–34 weeks. Extrarenal factors must contribute to the low serum Na values in infants with GA <31 weeks.     

Intestinal permeability in relation to birth weight and gestational and postnatal age

OBJECTIVE: To determine the relation between intestinal permeability and birth weight, gestational age, postnatal age, and perinatal risk factors in neonates. STUDY DESIGN: Intestinal permeability was measured by the sugar absorption test within two days of birth and three to six days later in preterm and healthy term infants. In the sugar absorption test, the urinary lactulose/mannitol ratio is measured after oral ingestion of a solution (375 mosm) of lactulose and mannitol. RESULTS: A first sugar absorption test was performed in 116 preterm (26-36 weeks gestation) and 16 term infants. A second test was performed in 102 preterm and nine term infants. In the preterm infants, the lactulose/mannitol ratio was not related to gestational age (r = -0.09, p = 0.32) or birth weight (r = 0.07, p = 0.43). The median lactulose/mannitol ratio was higher if measured less than two days after birth than when measured three to six days later (0.427 and 0.182 respectively, p<0.001). The lactulose/mannitol ratio was higher in preterm infants than term infants if measured within the first 2 days of life (0.404 and 0.170 respectively, p < 0.001), but not different three to six days later (0.182 and 0.123 respectively, p = 0.08). In multiple regression analysis of perinatal risk factors, only umbilical arterial pH correlated with the lactulose/mannitol ratio in preterm infants less than 2 days of age (T = -1.98, p = 0.05). CONCLUSIONS: In preterm infants (26-36 weeks gestation), intestinal permeability is not related to gestational age or birth weight but is higher during the first 2 days of life than three to six days later. It is higher in preterm infants than in healthy term infants only if measured within two days of birth. This suggests rapid postnatal adaptation of the small intestine in preterm infants.