The effect of maternal characteristics and gestational diabetes on birthweight

Abstract

Objective: To examine the effect of maternal characteristics, including advancing maternal age, body mass index (BMI), racial origin and development of gestational diabetes mellitus (GDM), on birthweight and the interactions between these factors.

Design: Retrospective analysis of prospectively collected data.

Setting: Fifteen maternity units in North West London, between 1988 and 2000.

Population: A cohort of 130 549 pregnant women.

Methods: Multivariate regression analysis.

Outcome measures: Birthweight z-scores in non-GDM and GDM groups within three main racial groups (white European, black and South Asian women).

Results: Babies born to women with GDM were heavier compared with those born to women with no GDM in all racial groups. In black women with GDM the birthweight z-scores were 0.805 higher, in South Asian women the scores were 0.618 higher and in white European women the scores were 0.437 higher, compared with the respective non-GDM group (P < 0.001 for both comparisons versus white European women), and these differences were much greater at high rather than at low maternal BMIs. Advancing maternal age, increasing BMI, highest diastolic blood pressure, Castair's index, racial group and presence of GDM or smoking were each, individually, significantly associated with birthweight z-scores (P < 0.001 for all variables). After adjusting for possible confounding factors, BMI was positively associated with birthweight z-scores within all racial groups (P < 0.001 for all), irrespective of glycaemic status, but its effect was much greater in women with GDM, particularly in those of non-White origin. After adjusting for possible confounding factors, advancing maternal age was only positively associated with birthweight in women of white European and South Asian racial origin who did not suffer from GDM (P < 0.001 for both).

Conclusion: Gestational diabetes mellitus strongly accentuates the effect of maternal BMI on birthweight, especially within non-white populations.