Background There has been concern that low gestational weight gain may cause poor fetal neurodevelopment.

Methods The association between maternal weight gain and child IQ was examined using serial antenatal weight measurements (median 12) from a prospective cohort of non-obese Scandinavian women (1986–1988). Linear mixed models with piecewise regression were used to estimate participants’ (n=552) trimester-specific average rate of weight gain. Linear regression was used to assess the association between weight gain and children's (n=344) full-scale, performance and verbal IQ measured at age 5 using the Wechsler Preschool and Primary Scales of Intelligence-Revised.

Results Children born to mothers who gained below versus within the 2nd trimester 2009 recommendations tended to have lower IQ scores (Full-scale: 106.6 (SD 15.1) vs 110.2 (15.2), p=0.04; verbal: 102.5 (14.3) vs 105.0 (14.9), p=0.10; performance: 109.5 (15.4) vs 113.4 (14.5), p=0.03). After adjustment there were no differences in child IQ by weight gain adequacy (full-scale: β_below=−1.1 (95% CI −5.1 to 2.9), β_above=1.5 (−3.8 to 6.8); verbal: β_below=−0.2 (−3.1 to 2.6), β_above=1.8 (−3.6 to 7.3); performance β_below=−1.2 (−4.6 to 2.2), β_above=1.0 (−4.6 to 6.7)). No differences were observed based on 3rd trimester adequacy. No differences were observed in IQ scores by quintile of weight gain for any trimester, particularly after adjustment for maternal IQ.

Conclusions Our findings are reassuring that among normal weight women, pregnancy weight gain is not associated with child cognitive development. Further investigation should be conducted in contemporary cohorts that also include obese mothers, who are at the greatest risk for low weight gain.