Increased body weight is one of the most important global health issues, affecting over 2 billion people worldwide (Engin, 2024). Maternal obesity creates a bad intrauterine environment and as a consequence may have adverse effects and a negative impact on the mother during pregnancy and on the infant in the beginning and later in life (Anstey et al., 2011).

Gestational weight gain (GWG) is a crucial physiological adaptation that occurs in response to the increased metabolic demands of the growing fetus. According to the Institute of Medicine (IOM) recommendations, for singleton pregnancies, the recommended total weight gain is approximately 12.5–18 kg for women who enter pregnancy underweight (BMI <18.5), 11.5–16 kg for those of normal BMI (18.5-24.9), 7-11.5 kg for overweight women (BMI 25-29.9), and 5–9 kg for women with obesity (BMI ≥30). In the context of twin pregnancies, the suggested weight gain thresholds are correspondingly higher: about 16.8-24.5 kg for women with a normal BMI, 14.1-22.7 kg for those who are overweight, and 11.3-19.1 kg for women with obesity (Weight Gain During Pregnancy).

Maintaining the appropriate weight gain dynamics is critical, as inadequate or excessive GWG are consistently associated with adverse maternal and neonatal outcomes that can impact long-term health status (Shekaili et al., 2024). Specifically, inadequate prenatal weight gain risks fetal growth restriction and preterm birth, while excessive weight gain (including pre-existing obesity, or obesity developing during gestation) is linked to a higher incidence of prematurity, fetal death, neonatal metabolic disturbances, and increased congenital risks for the child, such as neural tube defects and congenital heart defects (Shekaili et al., 2024; Ege et al., 2025).

While the fetal environment was traditionally considered sterile, some recent research has proposed the possibility of prenatal microbial exposure via the placenta and amniotic fluid (Li et al., 2024). However, this remains a subject of significant debate, with delivery mode and early postnatal factors currently recognized as the primary and most definitive drivers of initial gut colonization, with the surrounding environment, breast milk, feces, mouth, and skin being the primary sources of the first microorganisms for all newborns (Ma et al., 2023). During the initial months of life, the intestinal tract is transiently overpopulated by facultative anaerobes such as Enterobacteriaceae and Staphylococcus, which are quickly replaced by the “Bifidus flora,” a dominant population of Bifidobacterium and lactic acid bacteria that remains stable until the introduction of complementary solid foods. As the infant approaches weaning, the relative abundance of Bacteroides increases, gradually replacing Bifidobacterium and leading to an adult-type community dominated by Bacteroides, Prevotella, Clostridium, and Ruminococcus. This shift, typically resulting in an adult-like microbiota by three years of age, is significantly shaped by crucial environmental factors, including breastfeeding, type of delivery, and antibiotic exposure (Pantazi et al., 2023; Li et al., 2024).

Prior reviews suggested a relationship between maternal obesity and both maternal and infant gut microbiome, noting that increased pre-pregnancy body-mass index (BMI) was often linked to early differences in infant gut composition and alpha diversity. However, the authors concluded that the literature was highly heterogeneous, observing contradictory effects for GWG and emphasizing that any microbial differences were often nullified or weakened by postnatal factors like delivery mode and feeding (Grech et al., 2021; Mulligan and Friedman, 2017; Singh et al., 2017; Kumbhare et al., 2019; Dreisbach et al., 2020; Kapourchali and Cresci, 2020; O’Neill et al., 2020). Given that the gut microbiome remains an ever-evolving field of research, constantly revealing new pathways and interactions, there is a critical need to update and narrow the synthesis. Therefore, our review aims specifically to focus solely on the effects of GWG on the infant gut microbiome, in order to provide a more precise and current synthesis regarding this single, critical perinatal variable.

This systematic review was conducted according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement (Grainger and , 2025). A prespecified protocol was formulated and registered in PROSPERO (CRD 420251181399) and is available online (PROSPERO, [[NoYear]]).

A total of 1481 articles were initially retrieved from PubMed and Scopus. Out of the 79 of these who were assessed for eligibility, 14 met the inclusion criteria. One additional study was identified by screening the reference lists of the initially retrieved articles, resulting in a final total of 15 studies included in this systematic review (Kennedy et al., 2023; Collado et al., 2010; Chu et al., 2017; Robinson et al., 2017; Stanislawski et al., 2017; Baumann-Dudenhoeffer et al., 2018; Singh et al., 2020; Raspini et al., 2021; Gilley et al., 2022; Vacca et al., 2022; Song and Liu, 2023; Caprara et al., 2024; Xiao et al., 2024; Cho et al., 2025; Liu et al., 2025). The selection process is presented in the PRISMA flow diagram of the study (Figure 1).

The 15 studies were included in this review, yielded approximately 1723 participants. The included studies span a publication period of 15 years, ranging from 2010 to 2025. The studies were conducted across eight countries, with the USA now being the most represented (Chu et al., 2017; Robinson et al., 2017; Baumann-Dudenhoeffer et al., 2018; Singh et al., 2020; Gilley et al., 2022), and including also China (Song and Liu, 2023; Xiao et al., 2024; Liu et al., 2025), Italy (Raspini et al., 2021; Vacca et al., 2022), and one study each in Korea (Cho et al., 2025), Germany (Kennedy et al., 2023), Brazil (Caprara et al., 2024), Norway (Stanislawski et al., 2017), and Finland (Collado et al., 2010). The characteristics of the included studies are summarized in Table 1.

Our review, incorporating fecal samples form 1723 participants revealed that EGWG is a determinant of early infant gut characteristics, primarily manifesting as a reduction in alpha diversity that appears to be persistent over the first year of life. Taxonomically, this is linked to a notable shift away from beneficial genera, such as Bacteroides and toward the colonization of opportunistic and potentially harmful taxa.

In utero exposure to metabolic and nutritional disturbances such as those often accompanied or exacerbated by EGWG, is detrimental to the fetus’s well-being. This exposure is thought to reduce the child’s cardiometabolic health and cause long-term neurological defects, including motor development disorders, as well as increased risk for childhood overweight and obesity (Lackovic et al., 2024). Additionally, early pregnancy BMI and GWG independently influence offspring growth patterns, even from birth, were these factors were associated with birth weight. From birth to 18 months, GWG affected infant growth adversely, with excessive GWG leading to diminished growth trajectories (Österroos et al., 2024).

It is important to make the distinction between the effect of maternal p-BMI on the infant gut microbiome from the dynamic GWG, which constitutes a separate metabolic variable along with other related maternal factors, such as maternal lifestyle and diet (Liu et al., 2025). In regards to perinatal gut microbiota composition, GWG seems to affect the metabolic environment during pregnancy, leading to different microbial composition irrelevant to p-BMI, which also affects the earliest colonization patterns in meconium (Cho et al., 2025). This perinatally defined factor has outcomes that extend into later childhood, e.g. maternal overweight p-BMI correlates with both offspring gut microbiota composition and diminished cognitive development at 36 months of age (Guzzardi et al., 2022).

In the study by Cho et al., two distinct pathways through which maternal weight status influences the neonatal gut are suggested. In regard to p-BMI, it appears to set a basal metabolic environment, affecting early colonization through sustained maternal energy balance, adipokine signaling, and inflammatory regulation. On the other hand, GWG acts as a dynamic variable, altering the intrauterine metabolic status, possibly through changes in nutrient delivery, short-chain fatty acid transfer, or altered gut permeability (Cho et al., 2025). On the contrary, Stanislawski et al. reported that, while excessive GWG was associated with differences in the composition of the maternal gut microbiota at delivery, these changes resulted in only limited differences in the infants’ gut microbiota over the first two years, suggesting maternal weight is not a major determinant compared to factors like delivery mode, or breastfeeding. Nevertheless, the presence of specific maternal taxa (e.g., those vertically transmitted) translated to increased presence in the infant, suggests that the relationship of EGWG and infant gut microbiota is at least partially mediated by maternal gut microbiota composition during pregnancy, influencing early colonization and microbiome maturation. EGWG was linked to an increase in potentially harmful groups like C. difficile and the Staphylococcus aureus group and a higher proportion of Akkermansia muciniphila at one month of life, which all correlated with future growth parameters (Stanislawski et al., 2017).

As previously mentioned, the influence of these maternal characteristics, including EGWG on the infant microbiome appears to diminish over time, as the infant and its gut ecosystem become exposed to other, more potent factors. Primarily nutrition, including feeding type (breast milk or formula) and the introduction of solid foods, appears to be the key shaping factor later in life, followed by environmental factors like contact with pets and relatives (Laursen et al., 2016). It is worth mentioning that most studies failed to account for the quality of the maternal diet when determining this effect, despite the dominant role that nutrition plays in shaping the microbiome. Nevertheless, some studies suggest that once delivery mode and infant feeding status (e.g., exclusive breastfeeding), are accounted for, many dietary associations lose statistical significance. Despite the overall uncertainty of evidence, some data suggest that specific macronutrients have an independent impact. For example, diets rich in beneficial factors like fermentable fiber and vegetable protein are found to be associated with more favorable microbiotal diversities, while diets high in animal protein and fats can increase risks of adverse outcomes related to the microbiomic environment they foster (Rio-Aige et al., 2025).

This study has certain limitations. Firstly, the availability of evidence was restricted, as our literature search retrieved only15 relevant studies, all of which were designed as observational cohorts (although, as per our protocol, RCTs were eligible for inclusion, none were retrieved) and are therefore susceptible to residual confounding. Secondly, significant heterogeneity among the included studies, in terms of design, data collection methods, and analysis, prevented the performance of a meta-analysis and made direct comparisons challenging. Lastly, the variability of GWG categories definition may affect the robustness of our conclusions and decrease the strength and generalizability of our findings.

In conclusion, EGWG is an independent defining factor of infant gut dysbiosis. It affects microbial alpha diversity for up to 12 months, changing the taxonomic composition, from Bacteroides and other beneficial colonies toward opportunistic/pathogenic genera. Although EGWG is as a key modifiable maternal factor linking gestational health to long-term offspring health, the literature remains scarce. More randomized studies and pathway research are needed to determine the exact effect of EGWG on infant gut microbiota and the mechanisms orchestrating this interaction.