Gestational weight gain that is either above or below levels recommended in guidelines can lead to adverse outcomes for mother and baby, a world first study finds.

The analysis of over 1,000,000 pregnancies found that 51% of women had weight gain above and 20% had weight gain below levels recommended in IOM guidelines.

Lead author Dr Rebecca Goldstein from the School of Public Health and Preventive Medicine at Monash University in Victoria presented the findings from the one million gestational weight gain study at the ESA clinical oral highlights session on Monday afternoon.

The results of their systematic review and meta-analysis of 19 papers involving women across all weight categories found that women with a gestational weight gain (GWG) below guideline recommended levels had an odds ratio of 1.83 for having a baby that was small for gestational age.

For women who were obese this corresponded to an OR of 1.24.

Pooled odds ratios showed that preterm birth had the same pattern, with women with low weight gain having a high risk of preterm birth compared to those with weight gain higher than guideline recommended levels.

Women who had weight gain below guidelines had a lower risk for large gestational age, macrosomia and c-section compared to women who had weight gain above the guideline parameters.

 Women with ‘mild’ obesity at highest risk

A sub-group analysis conducted by the authors looking at the weight of women at the onset of pregnancy found that 67% of women were in the class I ‘mild’ obese range.

Half of these women had weigh gain above guidelines at the end of their pregnancy.

Weight loss corresponded to a lower risk of adverse outcome and weight gain above corresponded to a higher risk.

However Dr Goldstein said it was interesting to note that women classified as having mild obesity and had weight gain above recommended guidelines had the highest risk for having a baby small for gestational age and c-section.

“Weight loss and weight gain are protective… the highest risk in women with weight gain above guidelines are for those women in the class 1 obese range,” she said.

“Recommendations for women who are obese and overweight to lose weight needs to be considered with caution,” Dr Goldstein advised.

“Because we know that they do have a greater risk of SGA and preterm birth,” she said.