Birthweight is strongly and positively related to maternal preconceptional weight as well as with weight gain during pregnancy. Therefore, it would be expected that the increase in maternal weight before pregnancy, and weight gain during pregnancy, would be associated with an increase in birthweight in France. Animal models suggested that maternal weight changes in the periconceptional period can be considered as indicators of maternal energy balance and nutritional status, and may be involved in fetal growth and pregnancy outcomes.Obejective : 1) To evaluate time trends in maternal body size and birthweight. 2) To investigate the association of maternal weight changes in the periconceptional period with fetal growth and adverse pregnancy outcomes.Background : Birthweight is strongly and positively related to maternal preconceptional weight as well as with weight gain during preg Populations : Data were from ObEpi surveys ; French nationally representative perinatal surveys and the EDEN study. 1) For every ObEpi survey (1997, 2000, 2003 and 2006), data on weight and height were obtained for 20000 households representative of the French population.2) Mother-child pairs among singleton live births were included in the national perinatal surveys in 1972, 1981, 1995, 1998 and 2003 (n=8664, 4494, 11445, 12692 respectively). Mothers were interviewed a few days after delivery and data on delivery and the newborn were extracted from hospital records. 3) In the EDEN mother-child cohort, 1756 mother–child pairs had information on mother’s weight at 20 years, weight just before pregnancy, fetal anthropometry at second and third trimesters, infant’s birthweight and pregnancy complications. Also in the EDEN study 1744 women had prepregnancy weight available and at least 5 measures of weight in pregnancy. We extrapolated women’s weight at each week of gestation with a three-degrees polynomial model and estimated weight change during each trimester of gestation.Results : 1) Analyses based on data from ObEPI surveys showed that more recent cohorts (those born after the 1960’s) experienced an accelerated increase in the prevalence of obesity in relation to age during 1997-2006 particularly for women when compared with older birth cohorts. 2) Body mass index and weight gain during pregnancy increased between 1972 and 2003 ; paradoxically birth weight did not show a parallel increase. In fact, after adjusting for several potential confounders birthweight showed a decrease between 1995 and 2003.This corresponded with an increase in babies born small-for-gestational age (SGA) and a decrease in those born large-for-gestational age (LGA). 3) In women with BMI < 25 kg/m2, weight loss before pregnancy was associated with less fetal growth and increased risk of SGA.Factors including anemia and pathologies such as cancer were also considered but did not explain the findings. On the other hand, “large” weight gain between age 20 and pregnancy was associated with increased risk of gestational diabetes irrespective of overweight status of the woman. 4) Lastly, a significant association between the variation in maternal weightover the first trimester of pregnancy and fetal growth was noted even after accounting for the variation in weight over the last two trimesters. This association was independent of weight gain later in pregnancy and was partly explained by placental weight showing the importance of periconceptual nutritional status.Conclusion : Although the obesity epidemic became apparent in adults only in the 1990s in France, some of its origins can be found as early as the mid 1960s. The increasing trend in the prevalence of SGA in France, and in other countries such like the US, should prioritize research efforts towards a better understanding of the causes of this time trend. Our datasuggest that weight changes in periconceptional period could be taken into account when evaluating the obstetrical risk.
