A baby’s birth weight is strongly linked to how much weight their mother gained during the first half of her pregnancy, according to a study led by Drs. Shi Wu Wen and Ravi Retnakaran with Dr. Mark Walker. This is important because babies with a very low or high birth weight are at greater risk of complications.

This study published in JAMA Pediatrics is the first to show that the timing of weight gain during pregnancy is crucial. The research team weighed 1,164 women in Liuyang, China before pregnancy and at 10 points during their pregnancy.

They found that pre-pregnancy weight and weight gain over the first 18 weeks of pregnancy were strongly linked with infant birth weight, but weight gained in the second half of pregnancy was not. Other studies are needed to confirm these findings. Women planning on getting pregnant should consult Health Canada’s Pregnancy Weight Gain Calculator and speak with a health-care provider about how much weight they should gain during pregnancy.