[Abstract] Objective To investigate the relationship between maternal weight gain during pregnancy and neonatal birth weight. Methods 1000 cases of singleton primigravida were analyzed, pre-pregnancy height, weight and weight gain during pregnancy were measured and body mass index (BWI) was calculated, age 21-35 years. The weight gain during pregnancy was divided into three groups: light, normal and heavy. The birth weight of each newborn was recorded and correlation analysis was performed. Results The birth weights of newborns in the light, normal and heavy groups were (2872.56 ± 325.22) g, (3242.58 ± 412.31) g and (3427.66 ± 421.62) g, respectively, and the differences were statistically significant. Conclusion Maternal weight gain during pregnancy was positively correlated with neonatal birth weight. The relationship between maternal weight gain during pregnancy and neonatal birth weight was found to be positive. The birth weight of the newborn has an extremely important impact on the outcome of the delivery, and the control and prediction of the newborn weight has become a very important part of the current pregnancy care. We observed the effect of maternal weight and its change at different stages of pregnancy on neonatal birth weight, which is a guideline for maternal health care. In this study, we collected data on pregnant women and newborns who delivered in the obstetric ward of Changning District Maternal and Child Health Hospital in Shanghai in 2011 to investigate the relationship between maternal weight gain during pregnancy and neonatal birth weight. Data and methods Study population General data were collected from 1000 cases of full-term singleton primiparous mothers who underwent routine examination and delivered in the obstetric outpatient ward of Changning District Maternal and Child Health Hospital in Shanghai from January 1, 2011 to October 1, 2011, and a prospective observation cohort was established after obtaining informed consent according to the inclusion and exclusion criteria. The included cases met the following criteria: ① maternal age 21-35 years, no history of cardiovascular system, respiratory system, digestive system, endocrine metabolic system, etc.; ② primiparous, singleton pregnancy, gestational age of delivery 38-42 weeks; ③ good birth condition of newborns, no history of asphyxia, hypoxia and birth injury, and complete birth data of newborns, including weight and height, etc. Content and methods Collection of baseline information When the health care card was established at about 12 weeks of gestation, a questionnaire was used to collect basic information of pregnant women, including name, age, pre-pregnancy height, weight, menstrual history, maternal history, etc. Maternal weight measurement and grouping Pregnant women are monitored for weight changes during pregnancy under the guidance of a full-time obstetrician, and the gestational weeks are recorded and the weight of the same period is measured. The maternal weight gain during pregnancy was equal to the weight before delivery minus the pre-pregnancy weight (at 12-13 gestational weeks). The cases were divided into three groups according to the weight gain during pregnancy: light group i.e. weight gain ≤9kg, normal group i.e. weight gain 9-18kg and heavy group i.e. weight gain ≥18kg. Statistical analysis SPSS 10.0 software was applied for statistical processing. Data were expressed as i±s, and t-test was used to compare the means of the two samples. The average maternal weight gain during pregnancy was (14.67 ± 3.82) kg in the cases with the light, normal and partial groups being (7.56 ± 0.64) kg, (15.45 ± 1.79) kg and (20.78 ± 2.14) kg, respectively. 1000 newborns had a birth weight of (3147. 54 ± 462.38) g, of which 553 were male and 447 were female. 553 cases and 447 cases of female infants. The birth weights of newborns in the light, normal and partial weight groups were (2872.56 ± 325.22) g, (3242.58 ± 412.31) g and (3427.66 ± 421.62) g, respectively. the comparison of the mean birth weights of newborns in each group is shown in Table 1, and the differences were significant (P<0.05). Table 1 Comparison of birth weight status of newborns with different gestational weight gain groups Group (gestational weight gain) Number of cases Newborn birth weight (g) Light group (≤9kg) 145 2872.56 ± Normal group (9-18kg) 750 3242.58 ± Light group (≥18kg) 105 3427.66 ± Note: Group A compared with group B Group compared with group C Group compared with group C Comparison Discussion The proportion of overweight women of childbearing age in China is increasing due to various factors such as dietary structure, living habits and genetics. Studies have shown that overweight women of childbearing age are more likely to suffer from endocrine and lipid and glucose metabolism disorders, and are more likely to develop gestational hypertension and gestational diabetes during pregnancy. The pre-pregnancy weight of women of childbearing age also significantly affects the birth weight of the newborn, with women with low pre-pregnancy weight being significantly more likely to have a low birth weight baby and women with high pre-pregnancy weight being significantly more likely to have a large baby [1]. Several studies have shown that maternal weight gain during pregnancy should be controlled within a reasonable range, and that a 20-25% increase in weight during pregnancy is generally reasonable compared to pre-pregnancy [2-3]. In 1990, the Institute of Medicine (IOM) proposed a reference value for weight gain during pregnancy based on the pre-pregnancy body mass index (BMI), according to which when the pre-pregnancy BMI is less than 19.8 kg/m2, the weight gain during pregnancy should be controlled within the range of 12.5 to 18 kg, and when the pre-pregnancy BMI is less than (19.8 kg/m2), the weight gain during pregnancy should be controlled within the range of 12.5 to 18 kg. pre-pregnancy BMI is (19.8 to 26.0) kg/m2, weight gain during pregnancy should be controlled in the range of 11.5 to 16 kg, when pre-pregnancy BMI is 26.29 kg/m2, weight gain index during pregnancy should be controlled in the range of 7 to 11. 5 kg, and when pre-pregnancy BMI is greater than 29 kg/m2, weight gain during pregnancy should be in the range of 6 to 7 kg [4]. The data from this study showed that pregnant women gained an average of 14.81 kg during pregnancy, which is within the normal range of the reference value for weight gain during pregnancy provided by the Institute of Medicine, reflecting the high overall maternal health care standard of pregnant women who delivered in Changning District Maternal and Child Health Hospital in Shanghai and similar to the results of previous studies reported in the literature [4 -5]. One of the important indicators of neonatal health is the birth weight of the newborn, and maintaining a reasonable diet during pregnancy and keeping the weight gain within a reasonable range while ensuring nutritional intake has a significant and positive impact on the birth weight of the newborn. Overseas studies have shown that maternal pre-pregnancy weight and maternal weight gain are one of the key factors affecting neonatal weight, and they are significantly correlated with each other [6 -7]. Neonatal birth weight is positively correlated with maternal pregnancy weight gain when maternal pregnancy weight gain is controlled within the normal range, and the best maternal and infant pregnancy outcome is achieved when the newborn birth weight is between 2900 and 3499 g [8]. The data of this study showed that the mean birth weight of 1000 newborns was (3147. 54 ± 462.38) g , and the birth weights of newborns in the light, normal and heavy groups were (2872.56 ± 325.22) g, (3242.58 ± 412.31) g and (3427.66 ± 421.62) g respectively in agreement with the findings reported in the literature[9] . . Our study further confirms the previously reported findings that the more maternal weight gain during pregnancy is associated with an increase in neonatal birth weight. These phenomena should draw our sufficient attention because when the nutrition provided to the fetus by the pregnant woman greatly exceeds its consumption, it causes excessive accumulation of fetal fat, which leads to high neonatal weight and increases the likelihood of overweight or even obesity at all stages of later development, seriously affecting its health level and quality of life in adulthood. These possible far-reaching effects deserve further in-depth follow-up studies.