Mums who carry too much weight and/or who smoke during pregnancy increase the risk of having overweight kids, indicates a systematic analysis of the available evidence published online in the Archives of Disease in Childhood.
A high birth weight and rapid weight gain during the first year of life also increase the risk, indicates the study.
The authors base their findings on a comprehensive review of the available evidence, housed in reputable research databases, such as MedLine and PubMed, and published between 1990 and 2011.
They included only those studies which tracked children's health from birth until at least the age of two years, and which looked at potential risk factors before birth and up to the age of 12 months.
In all, 30 studies, involving more than 200,000 participants, were included in the analysis.
The results indicated several significant and independent factors that increased the risks of childhood overweight.
These were a mum who was overweight during the pregnancy; high birth-weight of the child; early rapid weight gain during the first year of life; and a mum who smoked during her pregnancy.
Smoking during pregnancy alone boosted the risk by 47.5%. But this may be because smoking is a good indicator of other social and lifestyle characteristics, say the authors.
Breastfeeding and late weaning helped to stave off childhood overweight, to some extent, the analysis showed. Breastfeeding cut the risk by 15%.
The evidence was mixed for length of breastfeeding, household income and marital status at the time of the child's birth, and how many other pregnancies the mother had had.
And no link was found between the mother's age, educational attainment, ethnicity or depressive symptoms and being overweight during childhood, while the evidence for type of delivery, weight gain during pregnancy, weight loss after pregnancy and whether the child was a "fussy" eater was inconclusive.
While there seem to be clear factors that increase the risk of childhood overweight, further research will be needed to explore the feasibility of using these in clinical practice to help healthcare professionals pick up infants at risk early on, conclude the authors.