Influence of elective preterm delivery on birthweight and head circumference standards.

Abstract

SUMMARY We calculated new birthweight and head circumference centiles for boys and girls between 24 and 42 weeks' gestation from 20 713 singleton live births at our hospital between 1978 and 1984. Among the 803 babies born at or before 34 weeks' gestation, 28% were delivered electively for fetal problems; they were considerably lighter than babies born after spontaneous preterm labour. In contrast, they showed only a small deficit in head circumference, possibly due to a brain sparing effect in growth retarded infants. Electively delivered preterm infants cause a bias in birthweight and head circumference centiles and we recommend that these babies should be excluded when these centiles are calculated.Commonly used tables of birthweight and head circumference centiles -5 differ from one another, varying both in the mean and spread of values at different gestational ages. These differences are likely to reflect differing degrees of accuracy in determining gestational age but also genuine differences in the populations from which the data were derived. A further problem is the lack of data relating to very early gestational ages, yet elective delivery of infants before 30 weeks' gestation is increasingly common.

Selection biases invalidate current low birthweight weight‐for‐gestation standards

“…3) largely disappeared if all infants bom electively (usually for pre‐eclampsia or small fetal size) were excluded from the sample. Others have reported a similar phenomenon 11,23,24 .…”

“…This study has shown that all previous European birthweight standards for infants < 28 weeks of gestation have been misleadingly high 9–15 , and that the lower limit of the normal range (the 3rd centile) has sometimes been overestimated by as much as 30% 12 . There can be no doubt that most of this bias has been caused by limiting the population sample to live births: the exclusion of intrapartum deaths at 23 to 26 weeks of gestation (18% of the final sample) increases median birthweight by nearly 10%.…”

“…While some North American studies have tried to provide normative data for such infants 1–4 , most European studies have avoided this challenge 5–8 . Furthermore, many of the published studies relate to the experience of a single institution 9–13 , and most of the population based studies have reported only on infants classified as liveborn 14–16 , which could bias the birthweight distribution especially for infants born in the second trimester of pregnancy. In the UK two most frequently used weight standards for infants born before 32 weeks 12,15 derive from hospital‐based samples that included only 80 and 97 live births at 24 to 27 weeks of gestation, respectively.…”

Human growth plate development in the fetal and neonatal period

“…Thus, <lo% of the cases reviewed (1,423) complied with the criteria of the study. In all of these cases, gross morphological parameters including the radiographic length of several bones were within the normal limits for the corresponding developmental age @,lo, 11,14, 22,25,27,29,32,35), thus supporting the normality, in terms of growth, of the individuals under study.…”

Gender-specific early postnatal catch-up growth after intrauterine growth retardation by food restriction in swine with obesity/leptin resistance

“…Symmetrical IUGR is characterised by a uniform reduction of the foetus and its organs from early pregnancy and is associated with genetic and infectious factors. Asymmetrical IUGR is characterised by a reduction in size in some organs, while the remaining organs are normal; the brain is usually less affected by undernutrition and maintains its mass in comparison with the other organs, both in humans and domestic mammals (Yudkin et al 1987, McMillen et al 2001, including swine (Town et al 2004). This is caused by a redistribution of foetal blood flow to protect a key organ like the brain (which is known as the 'brain sparing effect ';Rudolph (1984)) at other organ expenses.…”