Does maternal early pregnancy underweight influence neonatal birth outcome? A retrospective study in Liverpool

Abstract

The neonatal period is a sensitive indicator of a population’s health with birth weight acknowledged as the most important factor affecting the newborn. Both ends of the birth weight spectrum predispose to increased risk of subsequent obesity and/or disease. There is considerable research into neonatal consequences of maternal overweight/obesity but less into maternal underweight. This study used BMI groups to consider whether maternal early pregnancy underweight influences neonatal birth outcome, particularly birth weight, and whether such associations vary according to the degree of underweight. This retrospective study used Statistical Package for the Social Sciences (SPSS) to analyse anonymised data, from a three year period, for 23,664 women booking-in for care at Liverpool Women’s Hospital. Following data recoding, study participants were placed into BMI bands with underweight being separated into <18.5kg/m2 and 18.6-19.9kg/m2; the X2 test investigated potential associations (p=<0.05) between early pregnancy BMI, particularly underweight, and neonatal outcomes. Data were unavailable for 5.7% of the sample group. Incidence of maternal underweight (9.2% mean) decreased over the data period; the majority (6.3%) of the underweight women were in the 18.6-19.9kg/m2 group. Of the total births, 7.5% were low birth weight; such infants were more likely to be delivered to mothers in the underweight groups (p=0.00). Other adverse neonatal outcomes (Gestational Age, foetal growth, neonatal intensive care requirement) were also associated with maternal underweight. The risk of adverse neonatal outcomes was inversely associated with degree of maternal underweight. Cross-tabulations performed between variables other than maternal underweight indicated a variety of associations, underlining the multi-factorial nature of birth outcome. This study indicates that maternal early pregnancy underweight is associated with adverse neonatal outcomes with risk influenced by the degree of underweight. Recommendations are made for further research to adjust for confounding factors and extend the observations.