The mediating effects of gestational diabetes on fetal growth and adiposity in women who are overweight and obese: secondary analysis of the LIMIT randomised trial

OBJECTIVE

To describe the mediating effect of maternal gestational diabetes on fetal biometry and adiposity measures among overweight or obese pregnant women.

DESIGN

Secondary analysis of the LIMIT randomised trial.

SETTING

Public hospitals, metropolitan Adelaide, South Australia.

POPULATION

Pregnant women with body mass index (BMI) ≥25 kg/m² and singleton gestation.

METHODS

Fetal ultrasound measures at 36 weeks of gestation and baseline BMI from women randomised to the LIMIT trial Standard Care group (n = 912 women) were used to conduct causal mediation analyses using regression-based methods.

MAIN OUTCOMES MEASURES

Ultrasound measures of fetal biometry and adiposity at 36 weeks of gestation.

RESULTS

Increased maternal BMI was associated with increased measures of fetal head circumference [direct (unmediated) effect 0.18 (95% CI: 0.05-0.31), P = 0.005; total effect 0.17 (95% CI: 0.02-0.31), P = 0.018], abdominal circumference [direct effect 0.26 (95% CI: 0.11-0.41), P = 0.001; total effect 0.26 (95% CI: 0.11-0.42), P = 0.001] and estimated fetal weight [direct effect 0.22 (95% CI: 0.08-0.35), P = 0.002; total effect 0.22 (95% CI: 0.08-0.35), P = 0.002], with no evidence of mediation by treated gestational diabetes. There was no apparent association between maternal BMI and fetal adiposity measures, or mediation by treated gestational diabetes.

CONCLUSIONS

We show an important association between increased maternal BMI and fetal growth, not mediated by treated gestational diabetes. There was no association between increased maternal BMI and fetal adiposity measures, or mediation by treated gestational diabetes. Whether these findings represent 'saturation' in the effect of maternal BMI on fetal growth or the effect of treatment of GDM is unclear.

FUNDING

This project was funded by a 4-year project grant from the National Health and Medical Research Council (NHMRC), Australia (ID 519240); The Channel 7 Children's Research Foundation, South Australia; and the US National Institutes of Health (R01 HL094235-01).

TWEETABLE ABSTRACT

Increased fetal growth associated with maternal obesity is not mediated by gestational diabetes.

The characterisation of overweight and obese women who are under reporting energy intake during pregnancy

Background

Misreporting of energy intake is common and can contribute to biased estimates of the relationship between diet and disease. Energy intake misreporting is poorly understood in pregnancy and there is limited research assessing characteristics of women who misreport energy intake or changes in misreporting of energy intake across pregnancy.

Methods

An observational study in n = 945 overweight or obese pregnant women receiving standard antenatal care who participated in the LIMIT randomised trial. Diet, physical activity, psychological factors, body image satisfaction and dieting behaviour were assessed at trial entry (10–20 weeks gestation) and 36 weeks gestation. Energy misreporting status was assessed through the ratio of daily energy intake over basal metabolic rate. Logistic regression analyses were conducted with the dependent variable of under reporting of energy intake at study entry or 36 weeks in separate analysis.

Results

At study entry and 36 weeks, women were classified as under reporters (38 vs 49.4%), adequate reporters (59.7 vs 49.8%) or over reporters of energy intake (2.3 vs 0.8%) respectively. The prevalence of under reporting energy intake at 36 weeks was higher than at study entry (early pregnancy). Body mass index (BMI) at study entry and 36 weeks and socioeconomic status, dieting behaviour and risk of depression at 36 weeks were independent predictors of under reporting of energy intake.

Conclusions

Under reporting of energy intake was present in over a third of overweight and obese pregnant women and was higher in late compared to early pregnancy. Characteristics such as BMI, socioeconomic status, past dieting behaviour and risk of depression may aid in identifying women who either require support in accurate recording of food intake or attention for improving diet quality. Results were unable to distinguish whether under reporting reflects misreporting or a true restriction of dietary intake.

Trial registration

Australian and New Zealand Clinical Trials Registry ACTRN12607000161426, registered 9/3/2007.

Electronic supplementary material

The online version of this article (10.1186/s12884-018-1826-x) contains supplementary material, which is available to authorized users.

The effect of antenatal lifestyle advice for women who are overweight or obese on secondary measures of neonatal body composition: the LIMIT randomised trial

OBJECTIVE

To evaluate the effect of providing antenatal dietary and lifestyle advice on neonatal anthropometry, and to determine the inter-observer variability in obtaining anthropometric measurements.

DESIGN

Randomised controlled trial.

SETTING

Public maternity hospitals across metropolitan Adelaide, South Australia.

POPULATION

Pregnant women with a singleton gestation between 10(+0) and 20(+0) weeks, and body mass index (BMI) ≥25 kg/m(2).

METHODS

Women were randomised to either Lifestyle Advice (comprehensive dietary and lifestyle intervention over the course of pregnancy including dietary, exercise and behavioural strategies, delivered by a research dietician and research assistants) or continued Standard Care. Analyses were conducted using intention-to-treat principles.

MAIN OUTCOME MEASURES

Secondary outcome measures for the trial included assessment of infant body composition using body circumference and skinfold thickness measurements (SFTM), percentage body fat, and bio-impedance analysis of fat-free mass.

RESULTS

Anthropometric measurements were obtained from 970 neonates (488 Lifestyle Advice Group, and 482 Standard Care Group). In 394 of these neonates (215 Lifestyle Advice Group, and 179 Standard Care Group) bio-impedance analysis was also obtained. There were no statistically significant differences identified between those neonates born to women receiving Lifestyle Advice and those receiving Standard Care, in terms of body circumference measures, SFTM, percentage body fat, fat mass, or fat-free mass. The intra-class correlation coefficient for SFTM was moderate to excellent (0.55-0.88).

CONCLUSIONS

Among neonates born to women who are overweight or obese, anthropometric measures of body composition were not modified by an antenatal dietary and lifestyle intervention.