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An epidemiological study of small-for-gestational age infants: A case-control study of mothers who repeated small-for-gestational age births and multiparous mothers who had only one such birth

Read, Anne Winifred (1988) An epidemiological study of small-for-gestational age infants: A case-control study of mothers who repeated small-for-gestational age births and multiparous mothers who had only one such birth. PhD thesis, Murdoch University.

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Abstract

This case-control study, based on the total population of Western Australian mothers, is a comparison of the births of two groups of case mothers and their matched controls. The case groups were called ’repeater’ and 'non-repeater* mothers. Repeater mothers were women who had given birth to more than one small-for-gestational age (SGA) term infant whereas non-repeater mothers were multiparous women who had had only one such infant. The two groups of matched control mothers had had no SGA infants. All mothers with preterm births were excluded from the study. The hypotheses were –
1) repeater mothers differed from non-repeater mothers in terms of the antecedents of their SGA births
2) repeater mothers differed from non-repeater mothers in terms of the outcomes for their infants.

Data for the study were collected from multiple sources including Western Australian Midwives' Notifications, hospital records and maternal questionnaires. The aim was to make the information collected for each birth to each mother as complete as possible.

Descriptive and analytical results are presented. Repeater mothers are described in four groups according to their attained sibship size and the sequence of their SGA births. Comparisons of these groups indicated that different patterns of SGA birth sequences contributed in various ways to the overall differences found between repeaters, non-repeaters and controls.

The major part of the descriptive results includes three comparisons for most of the variables which relate to the index infant and parents - non-repeaters compared with repeaters, non-repeaters compared with their matched controls and repeaters compared with their matched controls. It was found that whilst non-repeater and repeater mothers and their index (SGA) infants showed similarities for some variables, there were significant differences between the two groups for others. For example, neonatal outcome for the index infants of non-repeaters was significantly worse than for the index infants of repeaters.

A further section of the descriptive results investigates total obstetric history for case and control mothers up to the birth of the index infant. Mothers were separated into those with two and those with three infants and sibships described in a longitudinal It manner. was found that two infant sibships differed from three infant sibships with regard to many of the antecedent and outcome variables investigated.

Multivariate analysis was carried out by logistic regression to determine which of the factors found to be significant in the descriptive results contributed independently to differences between non-repeaters and repeaters. Significant risk factors for repeating SGA births compared with non-repeater status were having three infants (rather than two), weight loss or static weight in the third trimester of pregnancy, smoking by the infant's father, maternal birthweight of less than 3000g or height of less than 155cm, and not knowing the morbidity history of their own parents.

For repeater mothers, smoking by the infant’s father was significantly associated with the 'disadvantaged' categories of socioeconomic measures such as being unemployed and renting (rather than owning) accommodation. In contrast, there were no significant associations between this group of smoking fathers and variables of a biological nature such as sex and congenital malformations of the infant, paternal height and birthweight. Thus it appears that paternal smoking acted as a measure of socioeconomic status although there may also have been a direct association between paternal smoking and fetal growth.

Although the tendency to repeat SGA term birth appeared to be related to socioeconomic conditions, maternal birthweight and height were also important and these factors may have been mediated by genetic and/or environmental circumstances.

It should also be noted that, for a small percentage of parity-one mothers, weight loss in pregnancy was predictive of repeater status and, for some of those mothers, was associated with a malformation in the previous infant.

Item Type: Thesis (PhD)
Murdoch Affiliation: School of Veterinary Studies
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: repository@murdoch.edu.au. Thank you.
Supervisor(s): Stanley, Fiona, Swan, Ralph and Hawkins, Chris
URI: http://researchrepository.murdoch.edu.au/id/eprint/52315
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