Various studies have consistently found that advanced maternal age is closely linked to an increased probability of GDM and its recurrence [7, 20]. An insightful prospective study reported that women who are 40 years or older face more than double the risk of developing GDM compared to women under the age of 30, with a prevalence rate of 9.8% vs. 4.1%, respectively [21]. Additionally, Claramonte Nieto et al. [22] found a noteworthy higher incidence of gestational diabetes recurrence among women aged over 40. For women who are younger than 30, there is an 85% likelihood of conceiving within one year. However, this probability decreases to 75% within the first 12 months once they reach the age of 30. As women age further to 35, the likelihood declines to 66%. By the time they reach 40, the probability decreases to 44% [23]. As age increases, there is a decline in both the quality and quantity of oocytes, leading to reductions in ovarian reserve, endometrial receptivity, and uterine tension. Moreover, aging is associated with a gradual decline in insulin production and action, increasing the risk of RGDM and negatively impacting the prognosis for both the mother and the infant [24, 25]. There are several factors that contribute to this trend. These include the global population aging, evolving societal norms, an increase in divorce rates and subsequent remarriages, changing attitudes of women in both the workplace and education, as well as the widespread availability and use of contraception. Therefore, pregnant women with advanced age who experienced GDM should be identified early in their pregnancy and offered blood glucose monitoring in any future pregnancy.

The findings from the Northern California Kaiser oral glucose tolerance test (OGTT) Registry revealed that out of the 22,351 pregnant women who were investigated, there was a noteworthy risk increase of 71% in GDM when there was a one- to two-unit increase in BMI between the first and second pregnancy [26]. In contrast, a reduction in BMI exceeding two units between the initial and subsequent pregnancy was associated with a 68% decrease in the likelihood of developing GDM (the average height of the study participants is 5 feet 4 inches, thus one BMI unit corresponds to 5.9 pounds) [26]. An elevated BMI between pregnancies can potentially result in $\beta$-cell fatigue, leading to insufficient insulin production to compensate for the increased insulin resistance associated with a subsequent pregnancy. The risk of GDM decreased when overweight or obese women with a BMI of 25 kg/m² or higher reduced their BMI by 1–2 units (relative risk [RR] 0.80, 95% confidence interval [CI] 0.65–0.99), or by more than 2 units (RR 0.72, 95% CI 0.59–0.89) [27]. On the other hand, there was an elevated risk observed when BMI increased by 4 units or more (RR 1.26, 95% CI 1.05–1.51) in comparison to women with a stable BMI (–1 to 1 units). Within the subgroup of women with a normal body mass index (BMI 25 kg/m²), the likelihood of experiencing recurring gestational diabetes mellitus heightened with a BMI increase of 2–4 units (RR 1.32, 95% CI 1.08–1.60) and a BMI increase of $\ge$4 units (RR 1.61, 95% CI 1.28–2.02) compared to women whose BMI remained consistent [27]. Enhancing insulin sensitivity through weight loss between pregnancies can help women counteract the insulin resistance associated with their second pregnancy. A randomized controlled trial, which included 199 participants, found that the risk of gestational diabetes recurrence was reduced by 21% when weight loss occurred prior to conception. In the same trial, the recurrence rate dropped by 82% when weight loss reached or exceeded 5% of the initial body weight [28]. The findings from this study indicate that overweight or obese women, especially those with a history of GDM, should focus on increasing weight loss after childbirth. It is recommended to avoid retaining excessive weight during pregnancy and gaining weight after giving birth in order to minimize the risk of developing GDM in subsequent pregnancies.

Schwartz et al. [29] conducted a study on 788 mothers with GDM who had consecutive births over a period of 10 years. The research revealed a significant negative correlation between the length of the gestational interval and the risk of recurrent GDM [29]. In women with gestational intervals greater than 24 months, the likelihood of developing GDM was 1.18 times higher compared to those with gestational intervals less than 24 months. However, Nohira et al. [30] discovered that a shorter duration between pregnancies actually raises the risk of GDM recurrence. This could be attributed to insufficient restoration of $\beta$-cell activity and depletion during the postpartum period, as well as exhaustion resulting from breastfeeding [30]. Another potential scenario involves a reduced duration between pregnancies and an elevated body mass index prior to reaching the second trimester of pregnancy [31]. Furthermore, a meta-analysis revealed no significant correlation between the gestational interval and the risk of developing RGDM [7]. Therefore, it is imperative to conduct additional research in order to ascertain whether the duration of the gestational period plays a role in the probability of GDM recurrence.

According to a study conducted by Getahun et al. [32], women who experienced GDM in their initial pregnancy had a significantly higher likelihood of developing GDM in their subsequent pregnancy. The research findings revealed that these women were thirteen times more prone to acquiring GDM during their second pregnancy [32]. In addition, women who experienced GDM during both their initial and subsequent pregnancies had a significantly higher probability, a fifteen-fold increase, of developing GDM in their third pregnancy, in comparison to women who did not have GDM in either their first or second pregnancy. Women who have previously had GDM during their first two pregnancies are significantly more likely to develop GDM again in their third pregnancy. In fact, their risk is 26 times higher compared to women without a history of GDM. Furthermore, it is estimated that around 30–69% of women who have previously had GDM in their first pregnancy will also experience GDM in their future pregnancies [33, 34]. Variations in the frequency of GDM recurrence exist across above studies, possibly attributed to regional disparities and different lifestyles. However, these results revealed that GDM history plays an important role in RGDM.

Spong et al. [35] found that RGDM is multifactorial and women with RGDM had higher 100 g OGTT levels. To reduce the chances of GDM reoccurring, it is recommended that women who previously had GDM undergo a glucose tolerance test during any subsequent pregnancies. Research has found that there is a higher likelihood of GDM recurrence when the blood glucose level is 10.0 mmol/L or higher after a 1-hour OGTT, and when the blood glucose level is 7.8 mmol/L or higher after a 2-hour OGTT following the consumption of 50 grams of glucose. Therefore, it is advisable for women with a history of GDM to follow this guidance for proactive management of their glucose levels during pregnancy [36]. The overall OGTT results from eight publications, as analyzed by Schwartz et al. [7] in their meta-analysis, were found to be statistically significant. A retrospective study conducted on women in southern China revealed that OGTT 1 h and OGTT 2 h were found to be independent risk factors for RGDM in southern Chinese women. Specifically, women who had fasting plasma glucose (FPG) + OGTT 1 h + 2 h levels exceeding 23.6 mmol/L during their initial pregnancy were observed to have a significantly elevated risk of developing RGDM in their subsequent pregnancy [37]. A longitudinal retrospective study conducted in Canada revealed that women who have previously experienced macrosomia are at a 40% higher risk of developing RGDM compared to women with infants weighing between 2500–3999 grams [38].

The correlation between the severity of glucose rise during OGTT and the recurrence of gestational diabetes has been extensively documented. Moreover, there is a demonstrated association between insulin levels and RGDM. A research study conducted in Korea revealed that the RGDM group exhibited elevated fasting insulin concentrations, but experienced a notably lower increase at 1 hour (275 $\pm$ 250 vs. 400 $\pm$ 270 pmol/L) [39]. Furthermore, it has been observed that a reduced insulin level within one hour is an independent predictor of RGDM. This finding suggests that the reservoir for insulin secretion may be compromised in individuals with RGDM. Patients who exhibit inadequate $\beta$-cell compensation for insulin resistance during pregnancy are at a higher risk of developing RGDM in subsequent pregnancies [40].

Today, over-nutrition and sedentary habits are the result of changes in dietary patterns and lifestyle. A research study carried out in China has revealed that specific dietary patterns, such as excessive sugar and seafood consumption, along with exposure to secondhand smoke at home (odds ratio [OR] = 1.52, p = 0.027) and in the workplace (OR = 1.71, p = 0.01), are recognized as significant risk factors for RGDM [41]. A prospective randomized clinical trial conducted at Peking University First Hospital in China revealed that pregnant women who initiated supervised stationary cycling during early pregnancy and continued for a minimum of 30 minutes per session experienced a decreased likelihood of developing gestational diabetes. It is worth noting that 45.8% of pregnant women are classified as overweight or obese [42]. Moreover, a meta-analysis of longitudinal or cohort studies involving 30,871 pregnant women demonstrated that engaging in physical exercise before or during pregnancy can reduce the risk of GDM by 30% and 21% respectively, compared to a sedentary lifestyle [43]. Women who were pregnant and engaged in physical exercise for a minimum of 90 minutes per week during their leisure time experienced a 46% lower risk of GDM [33]. However, a randomized controlled trial of 205 pregnant women reported no significant benefit of exercise on RGDM (40% [n = 34] in the control group; 40.5% [n = 34] in the exercise group; p = 0.95), and a similar glycemic and insulin response to the OGTT (blood glucose at 2 hours after the OGTT was 7.7 $\pm$ 1.5 mmol/L in the control group and 7.6 $\pm$ 1.6 mmol/L in the exercise group; p $>$ 0.05) [44].

Breastfeeding has been shown to be protective against the onset of type 2 diabetes following GDM. In a study conducted on a cohort of 210 women who had previously experienced gestational diabetes and subsequently became pregnant, the results of an OGTT indicated that those who engaged in intensive breastfeeding exhibited significantly reduced blood glucose levels at the 2-hour mark (0.66 mmol/L, 95% CI 0.15–1.17; p = 0.01) [45]. Additionally, women who breastfed for more than six months demonstrated a significant decrease in their blood glucose levels one hour after (0.67 mmol/L, 95% CI 0.16–1.19; p = 0.01) [45]. According to a retrospective cohort study conducted by Zuarez-Easton et al. [46], it was found that the practice of exclusive breastfeeding for a minimum period of one month can reduce the probability of GDM recurring and potentially decrease the risk of developing coeliac disease (CD) in subsequent pregnancies.

Regarding the immediate impact, GDM is linked to an increase in hypertensive disorders, infections, ketoacidosis, excessive amniotic fluid, birthing complications, medical necessity for a cesarean section, postpartum hemorrhage, and labor induction [47, 48, 49, 50]. Postpartum women with GDM face an elevated risk of developing impaired glucose metabolism, cardiovascular disease, obesity, and psychoneurological issues [2, 4, 48, 49, 50, 51, 52, 53]. A meta-analysis revealed that women diagnosed with GDM are at a significantly higher risk of developing type 2 diabetes during pregnancy, compared to those with normal glucose tolerance [54]. Furthermore, the cumulative incidence of type 2 diabetes over follow-up periods ranging from 6 weeks to 28 years post-delivery was observed to be between 2.6% and 70%. During an OGTT, elevated fasting blood glucose levels are closely linked to a heightened risk of GDM advancing to type 2 diabetes mellitus [55].

A retrospective analysis was performed on 424 pairs of successive pregnancies with GDM. The study observed a significant reduction of nearly 50% in the occurrence of instrumental deliveries and emergency caesarean sections in subsequent pregnancies compared to the initial GDM pregnancies. However, there was an upward trend in the rates of planned caesarean sections, while the rates of normal deliveries and labor interventions decreased [56]. Another study conducted on 861 women who experienced GDM more than once revealed a higher likelihood of developing thyroid disease in subsequent pregnancies compared to their first pregnancy (6% vs. 10%, p = 0.003) [37]. Furthermore, women with recurrent GDM exhibited increased obesity, insulin resistance, and poorer blood glucose levels upon diagnosis [20].

GDM has the potential to cause various complications in the fetus. These may include birth defects, macrosomia (excessive birth weight), neonatal hypoglycemia (low blood sugar levels in the newborn), neonatal respiratory distress syndrome, and in severe cases, stillbirth [48, 49]. Furthermore, a population-based study has indicated that the risk of congenital malformations in infants born to mothers with GDM is significantly higher compared to the general population [57]. These malformations can affect various systems in the body, including the neurological system (such as brain and neural vessel defects, spinal cord abnormalities, and tail degradation syndrome), the circulatory system (including congenital heart defects and abnormalities in major blood vessels), bone development, and the urinary and digestive systems. Moreover, a substantial body of epidemiological evidence suggests that individuals who were exposed to GDM during the fetal stage are more susceptible to obesity and abnormal glucose tolerance during adolescence. In addition, they have a higher likelihood of developing diabetes mellitus, hypertension, and coronary heart disease in adulthood. Furthermore, there is evidence to suggest that GDM may impact the reproductive system development in the offspring [58]. Further study has indicated a strong association between GDM and atypical brain development in children. This correlation has been observed to manifest as challenges related to attention and cognitive abilities. Additionally, a retrospective study conducted in 2015 demonstrated a significant link between GDM and increased susceptibility to autism in children [59].

In addition to the observed effects in pregnancies with GDM alone, the presence of pre-existing diabetes (RGDM) significantly elevate the chances of delivering a baby with macrosomia (RR 1.76, 95% CI 1.56–1.98), encountering shoulder dystocia (RR 1.98, 95% CI 1.46–2.70), and experiencing preterm birth (RR 1.68, 95% CI 1.44–1.96) [60]. A retrospective longitudinal study was conducted on 389 women with GDM who experienced two consecutive pregnancies. The study aimed to investigate the variations in fetal weight and pregnancy outcomes. Among the total number of pregnancies included in this study, 181 (46%) demonstrated an increase in birth weight. However, further analysis revealed that only 125 (69%) of these infants exhibited a statistically significant increase in birth weight, exceeding 250 grams. The average increase in birth weight among these infants was found to be 531 $\pm$ 49 grams. Furthermore, it is noteworthy that the mean fetal weight varied between the two pregnancies for a subset of 130 out of 389 pregnancies (33.4% of the total sample). The average fetal weight for this subset was 373 $\pm$ 31 grams [61]. In contrast, there were no differences observed in maternal weight gain, gestational age at birth, mean blood glucose levels, macrosomia, and rates of large-for-gestational-age (LGA) infants. The neonatal outcomes remained consistent between both pregnancies, with no changes observed in the rates of stillbirth, shoulder dystocia, requirement for respiratory support, or admission to the neonatal intensive care unit [61].

Doses greater than 10⁷ colony-forming units (CFUs)/day positively affect the metabolic health of pregnant women. At a dose of 6 $\times$ 10⁹ CFUs/day of probiotic rhamnose HN001, the incidence of GDM is reduced [62]. The glucose metabolism and insulin sensitivity were improved by administering inositol and the probiotics L. rhamnosus GG and Lactobacillus acidophilus BB12 during the 12th and 14th weeks of pregnancy. Supplementing with a dose of 2 $\times$ 10⁹ CFUs of the mentioned bacteria, including Lactobacillus acidophilus, Lactobacillus casei, Bifidobacterium bifidum, and Lactobacillus fermentum, has shown a significant reduction in fasting glucose levels. Additionally, the specific combination of 109 CFUs of Bifidobacterium bifidum and Lactobacillus acidophilus has been found to promote glucose metabolism effectively [63].

Insulin sensitivity can be enhanced through various physical activities. These include engaging in aerobic exercises like walking, swimming, cycling, prenatal exercises, as well as mild to moderate strength training sessions. Engaging in daily physical activity for a duration of 30 minutes is highly recommended [64]. Expectant mothers should be cautious of their positions and avoid supine positions, contact sports, tennis, horse riding, sailing, and skiing due to the potential risk of preterm labor. It is crucial for pregnant women to maintain hydration and refrain from intense physical activity in hot or humid environments, or when they are experiencing any discomfort or hunger during exercise. They should also receive proper education on monitoring their fasting and post-meal blood glucose levels, as well as keeping a detailed record of their diet and physical activity to share with their healthcare providers [65].