Body size and neonatal hypoglycemia in intrauterine growth retardation

Proposing a new approach to measuring birth size asymmetry

BACKGROUND

Existing methods of measuring birth size asymmetry based on ratios of growth parameters are clinically useful but simplistic, and as such may have limited usefulness in studies of aetiology.

OBJECTIVES

We aimed to develop a novel method of measuring asymmetric fetal growth at birth and demonstrate its utility in characterising the perturbed growth associated with a number of prenatal exposures and neonatal outcomes.

METHODS

Data were drawn from the Queensland (QLD) Perinatal Data Collection, which included all livebirths in the Australian state of QLD between July 2010 and December 2015, with analyses restricted to babies born between 32 and 42 weeks of gestation (n = 280 084). Novel measures of asymmetric birthweight, length, and head circumference were developed using a weighted average, representing "how far" an individual's given birth size measure deviated from the sample average and their other birth size measures. Associations among prenatal exposures and neonatal outcomes with the new asymmetry measures and traditional ratio measures (ie ponderal index, brain-to-body weight ratio, and birth length divided by head circumference) were then compared using log-binomial and multinomial regressions.

RESULTS

The new asymmetry measures clearly indicated that prenatal smoking was linked to a disproportionate decrease in all birth size measures and that low birthweight asymmetry and low birth head circumference asymmetry were specifically associated with neonatal respiratory distress and chromosomal abnormalities, respectively. When these same associations were tested using the traditional ratios, the estimates were weak, imprecise, and non-specific.

CONCLUSIONS

We developed a new approach to measuring fetal growth asymmetry which provides complimentary insights against the existing ratios approach. Associations with the new asymmetry measures were more precise and easier to interpret than the associations obtained using the ratios, and may better reflect the underlying pathological processes, providing an advantage when investigating the aetiologies of perturbed fetal growth.

Glucose Homeostasis in Newborns: An Endocrinology Perspective

Physiologic adaptations in the postnatal period, along with gradual establishment of enteral feeding, help maintain plasma glucose concentrations in the neonatal period. The definition of normal plasma glucose in the neonatal period has been a subject of debate because of a lack of evidence linking a set plasma or blood glucose concentration to clinical symptoms or predictors of short- and long-term outcomes. However, there is consensus that maintaining plasma glucose in the normal range for age is important to prevent immediate and long-term neurodevelopmental consequences of hypoglycemia or hyperglycemia. The specific management strategy for abnormal glucose levels in neonates depends on the underlying etiology, and interventions could include nutritional changes, medications, hormone therapy, or even surgery. Here, we will review the physiological processes that help maintain plasma glucose in newborns and discuss the approach to a newborn with disordered glucose homeostasis, with an emphasis on the endocrine basis of abnormal glucose homeostasis.

Small and growth-restricted babies: drawing the distinction

The terms "small for gestational age" and "intrauterine growth restriction" have been used interchangeably to denote an in utero growth-restricted neonate. However, the two terms are not synonymous; not all small babies are growth restricted and not all growth-restricted ones are small. Research evidence, extending back to the middle of the last century, reveals that the number of growth-restricted babies who escape attention is not negligible and that the postnatal outcome of these babies is not uneventful. This paper highlights this issue and further discusses the available diagnostic tools for the identification of in utero-restricted neonates, that is, clinical assessment, anthropometric indices and obstetric ultrasound. Each of these tools has strengths and limitations, but, if combined, each could complement the other and help differentiate well-grown babies from those who are growth restricted.

CONCLUSION

Identification of growth-restricted neonates is feasible through the integrated use of diagnostic tools.

Metabolic adaptation in small for gestational age infants

Hypoglycaemia has long been recognised as a feature of the failure of metabolic adaptation in infants who are small for gestational age (SGA). This study examined the process of metabolic adaptation by measuring, longitudinally, the concentrations of metabolic fuels and substrates in 33 SGA infants in the first postnatal week, and relating these to cross sectional data in 218 infants of appropriate weight for gestational age (AGA). SGA term infants had higher mean blood lactate concentrations than AGA term infants at delivery (2.98 v 2.10 mmol/l) and in the first few postnatal hours (3.05 v 1.91 mmol/l). Subsequently, although there were no differences in blood glucose concentrations, SGA term infants had lower mean ketone body concentrations (for example day 2: 0.07 v 0.41 mmol/l), and failed to mount a ketogenic response to low blood glucose concentrations. At birth, SGA preterm infants had lower mean blood glucose concentrations than AGA preterm infants (3.17 v 4.16 mmol/l), but there were few postnatal metabolic differences between the two groups. Mean blood glucose concentrations did not differ between AGA and SGA preterm infants. For variables that differed between the groups, multiple regression analysis suggested that both the degree and asymmetry of growth retardation were related to the severity of the metabolic abnormalities. These data suggest that, although there are early metabolic differences between SGA and AGA infants, it is possible that current clinical management is effective in preventing subsequent hypoglycaemia. This is important because of the failure of SGA infants to mount a ketogenic response.

Prediction of impaired metabolic adaptation by antenatal Doppler studies in small for gestational age fetuses

The increased risk of hypoglycaemia for infants who are small for gestational age (SGA) is well known, and further information regarding metabolic adaptation can be gained by examining the profiles of glucose and other metabolic fuels in such infants. Not all SGA infants experience hypoglycaemia, however, and the ability to identify, antenatally, those at most risk would be helpful for obstetric and neonatal management. This study investigated metabolic differences between two groups of SGA infants who had antenatal umbilical artery Doppler studies. Fourteen had end diastolic velocities (EDV) present and 11 had absent EDV. The absent EDV group had significantly lower non-esterified fatty acid (NEFA) concentrations at birth, and lower blood glucose and NEFA concentrations in the first six hours after birth. After the first day, few metabolic differences were found between the two groups. Antenatal Doppler studies may identify those SGA infants who fail to achieve neonatal metabolic adaptation and are most at risk of early neonatal hypoglycaemia.

Differences in early postnatal morbidity risk by pattern of fetal growth in Argentina

Information on a cohort of 5539 singleton births delivered at term in two hospitals in Rosario, Argentina, was used to examine differences in early postnatal morbidity between small for gestational age (SGA) infants classified by their ponderal index (PI). SGA infants with low PI (SGA-LPI) were 4.35 (90% CI: 1.50, 12.61) times more likely to have asphyxia, 13.75 (2.48, 76.31) times more likely to have hypoglycaemia and 2.32 (1.03, 5.26) times more likely to have respiratory distress (RD) than SGA infants with adequate PI (SGA-API). The increased risks of asphyxia and hypoglycaemia observed for SGA-LPI infants diminished, but remained statistically significant after controlling for the infant's gender, birthweight, gestational age and hospital of birth. There was no difference in risk of hyperbilirubinaemia between SGA-API and SGA-LPI infants. With the exception of risk of hyperbilirubinaemia, SGA-API infants carried the same risks of morbidity as non-SGA infants. The results of the study show that SGA infants do not constitute a homogeneous group with respect to their prospects for early postnatal health and survival. Furthermore, the pattern of differences in morbidity risk between SGA-API and SGA-LPI infants observed in this study is consistent with the timing hypothesis for the aetiology of variation in PI among SGA infants.

The differential neonatal morbidity of the intrauterine growth retardation syndrome

This is a prospective study of differential morbidity among subgroups of intrauterine growth retardation. Cases of intrauterine growth retardation (N = 3450) (greater than or equal to 37 weeks, less than 10th percentile birth weight for gestational age) were classified by their ponderal index (weight/length3) in four subgroups using the 10th, 25th, and 90th percentiles of the Lubchenco's ponderal index-gestational age distribution. There were 432 cases (12.5%) with low ponderal index or disproportionate intrauterine growth retardation, 936 (27.1%) with intermediate ponderal index, 2030 (58.8%) with adequate ponderal index or proportionate intrauterine growth retardation, and 52 (1.5%) with high ponderal index. The low ponderal index group or disproportionate intrauterine growth retardation group had a statistically significant higher risk (between 1.6 and 12.5 times) for low 1- and 5-minute Apgar scores, aspiration syndrome, hypoglycemia, and perinatal asphyxia than the adequate ponderal index group. The low ponderal index group also had an increased risk (relative risk = 2.0 [95% confidence interval, 1.0 to 3.8]) for hospital stay of more than 1 week. These differences persist after a stratified analysis by birth weight and in a multiple logistic regression analysis. Similarly, higher neonatal morbidity is observed among infants with normal birth weights but with low ponderal index. These data provide further evidence of the heterogeneity of the intrauterine growth retardation syndrome and of the independent effect of body disproportion on neonatal morbidity, even among infants with normal birth weights. Because there are significant clinical implications attributed to the low ponderal index group, this subgroup should be identified as early as possible.

Effectiveness of ultrasound determination of fetal abdominal circumference and fetal ponderal index in the diagnosis of asymmetrical growth retardation

A total of 310 unselected women attending an antenatal clinic was screened for growth retardation by ultrasound between 34 and 36 weeks gestation, by measuring the fetal abdominal circumference (AC) and femoral length (FL), from which the 'fetal ponderal index' (AC/FL) was calculated. Asymmetrical growth retardation in the newborn was assessed by Rohrer's ponderal index and the mid-arm/occipito-frontal circumference (MAC/OFC) ratio within 72 h of birth, a neonatal ponderal index or MAC/OFC ratio below the 10th centile being considered abnormal. The sensitivities of an AC below the 25th centile in identifying a birthweight, neonatal ponderal index or MAC/OFC ratio below the 10th centile were 86, 62 and 67% respectively, the specificities being 80, 78 and 76%. The sensitivities of a fetal ponderal index below the 25th centile in identifying a neonatal ponderal index or MAC/OFC ratio below the 10th centile were 52 and 47% respectively, the specificities being 77 and 77%. A possible reason for the poor performance of the fetal ponderal index is discussed.

Indices of fetal growth-retardation, perinatal hypoxia-related factors and childhood neurological morbidity

Data from seven-year-old children (N = 4535) who were enrolled prenatally during the 1960s and born at term in the Boston sector of the National Collaborative Perinatal Project (NCPP) have been used to study the association of 7-year neurological morbidity with symmetric and asymmetric intrauterine growth-retardation (IUGR), head circumference at birth, and perinatal hypoxia-related factors (PHRF). In the absence of hypoxia-related factors, symmetric and asymmetric IUGR children were not at higher risk for neurological morbidity compared to non-IUGR children. In the presence of perinatal hypoxia-related factors, IUGR children were more likely to be neurologically abnormal compared to non-IUGR children, and the more severe form of IUGR (symmetric) appeared to be associated with a slightly higher risk than was the asymmetric form. Small head circumference was associated with increased risk of neurological abnormality regardless of the presence of PHRF. Potential metabolic and neurodevelopmental explanations for these findings are discussed.

The body proportions for small-for-dates infants

Measurements of weight, head circumference, crown-heel length, crown-rump length, rump-heel length and limb lengths were made in 514 neonates. From these measurements the differences in trunk and limb growth and their relations with head growth and body weight were examined in small-for-gestation (SGA) and appropriate grown (AGA) infants, and in different ethnic groups. We found that Asian infants had different body proportions from blacks and whites, with shorter trunks and forearms. SGA infants as a whole showed little difference in proportions from AGA infants except in their ponderal indices and the ratio of head size to body weight. However there was a preponderance of thin, relatively well-grown infants among them. When very short SGA infants were compared with AGA infants significant differences emerged, the short infants of all ethnic groups having shorter trunks and forearms in relation to their other measurements. We found no evidence of relative sparing of head growth. The results suggest that infants with prolonged intrauterine growth retardation are most likely to have disturbed skeletal proportions.

Patterns of retarded fetal growth

The measurement of weight, length and head circumference at birth was used to document the size and shape of infants born at term in a population where mothers are relatively short and underweight. Different patterns of intrauterine growth are proposed to explain the variation in the infant's appearance at birth. Most of the small-for-gestational-age infants were proportionately stunted. This pattern of fetal growth is probably characteristic of infants born to undernourished mothers in economically developing communities, and reflects prolonged intrauterine growth retardation.

Nutritional status of light-for-date infants at birth and its influence on early postnatal growth

The ponderal index (PI) (g/cm3 X 100) was used to define the state of nutrition at birth of 47 light-for-date (LFD) term infants and to determine how intrauterine undernutrition influences growth during the first 6 months of postnatal life, at four age intervals: birth--4, 5--8, 9--12, 13--26 weeks. With the exception of one baby, each PI was less than 50th centile on the Miller and Hassanein standards: in 24 (51%) babies the PI was less than 3rd centile. This suggests that, generally, LFD infants are underweight for length, and by inference, are likely to have experienced intrauterine undernutrition. In the first month the 24 'wasted' infants (PI less than 3rd centile) gained more rapidly in weight, and grew more quickly in head circumference and length than the 16 'nonwasted' infants (PI greater than 10th centile). Thereafter growth rates were similar. With the exception of weight in the 'nonwasted' infants during the first month, rates of growth (weight, length, and head circumference) in both groups of babies in each of the 3 months after birth were greater than in normal infants. The first 3 months after birth can therefore be defined as the period of 'catch-up' growth in LFD term infants.

Foot length--a new and potentially useful measurement in the neonate

The foot length, occipito-frontal head circumference (OFC), crown-rump, and crown-heel length (CHL) of 123 neonates of gestational ages 26-42 weeks, were measured between 12 hours and 5 days. A gauge, designed and constructed at St Mary's Hospital, Manchester, was used to measure foot length. In term babies (37-42 weeks) who were of weights appropriate for gestational age (AGA) the scatter about the mean of foot length measurements was small (coefficient of variation = 4.5%) compared with birthweight (coefficient of variation = 12.0%). The wide range of foot length measurements in babies of different gestational ages prevented maturity being accurately estimated. The mean birthweight of term light-for-dates (LFD) babies was 30.9% lower than term AGA babies, whereas the mean foot length, OFC, and body length of LFD babies was reduced by only 4.2-8.8%. There was a positive linear correlation between foot length and other indices of body size in LFD and AGA babies of all gestational ages. However, in premature babies (less than 37 weeks) the correlation between foot length and birthweight (r = 0.95) and foot length and CHL (r = 0.96) was pronounced. The 95% confidence limits of the regression lines were +/- 327 g and +/- 2.3 cm respectively. Birthweight and CHL of premature babies can therefore be estimated from a measurement of foot length that is performed simply and rapidly. Measurements of foot length are valuable in premature babies who are too ill at birth for conventional anthropometric measurements to be made, and in whom such measurements cannot be carried out subsequently because of the encumbrance of the incubator and intensive care apparatus. Drug dosages and intravenous fluid requirements based on body weight or surface area can be indirectly calculated from a measurement of foot length.