Most pregnant women with HBV infection were classified as chronic HBsAg carriers . The global prevalence of HBsAg in pregnant women has been estimated to be 5.0% . In China, the prevalence of maternal HBsAg has declined in recent years; however, it was higher than the global average . According to a study from 2018, the prevalence of HBsAg in pregnant women has declined from 9.8 to 6.3%, while more recent studies have reported a prevalence ranging from 7.0 to 9.4% [5,6,7]. In our retrospective cohort of 39,539 women, we found that 7.7% of pregnant women tested positive for HBsAg, consistent with the latter studies.
Recent reports have found that being a chronic HBV carrier was associated with adverse pregnancy outcomes such as GDM [22,23,24]. GDM was traditionally defined as carbohydrate intolerance of variable severity with onset or first detection during pregnancy. The latest meta-analysis from 2019 showed that 14.8% of pregnancies in China were complicated by GDM, increasing prevalence . GDM was one of the most common medical complications during pregnancy, associated with adverse pregnancy outcomes, including hypertensive disorders, preterm labor, neonatal hypoglycemia, hyperbilirubinemia, and respiratory distress syndrome. It was necessary to highlight the significance of understanding risk factors and specifically modifiable factors for GDM and prevent the condition, which might lower the risk of GDM-related adverse maternal and neonatal outcomes. Nowadays, the most common risk factors of GDM include older maternal age, obesity, and a family history of diabetes . Whether being HBsAg positive, a history of PCOS, and smoking or alcohol consumption during pregnancy are risk factors of GDM remains uncertain.
In our retrospective cohort of 39,539 women, we found that maternal HBsAg carriers have a higher risk of GDM (12% vs. 9.7%, OR 1.42, 95% CI 1.01–2.00). Being HBsAg positive was an independent risk factor of GDM. Several studies supported this finding. Lao et al.  analyzed 13,683 women in Hong Kong between 1998 and 2001 and found that the rate of GDM was statistically higher in pregnancies with an HBV infection (12.4 vs. 10.2%, OR 1.24, 95% CI 1.01–1.51). In 2016, Tan et al.  concluded that the rate of GDM in HBsAg carriers was higher than non-HBsAg carriers (11.8 vs. 8.2%, OR 1.41, 95% CI 1.15–1.74) in a case–control study 22,374 Chinese women. The latest meta-analysis from 2018 demonstrated that women with HBV infection had an increased risk of GDM (6.48% vs. 3.41%, OR 1.35, 95% CI 1.17–1.56) . However, a few previous studies have shown the connection between maternal HBV infection and the development of GDM to be insignificant. Reddick et al.  showed that the incidence of GDM among HBsAg positive women (4.4%) was similar to that of HBsAg negative women (2.5%, P > 0.05). Cui et al.  found the incidence of GDM between the HBV infected women and non-HBV women to be insignificant (1.17% vs. 1.13%, P > 0.05) in a prospective cohort study involving 21,004 pregnant women. Furthermore, our study found that older maternal age and obesity were associated with a higher risk of GDM, consistent with the previous studies.
The potential mechanism for the correlation between HBsAg and GDM is unclear. The liver is an important organ that handles liver glucose metabolism and the development of insulin resistance. Liver disease and inflammation caused by HBV during pregnancy may lead to reduced insulin sensitivity . Another mechanism could be that HBV-infected pregnant women display a spontaneously increased production of tumor necrosis factor-alpha, which contributes to insulin resistance leading to the development of GDM [28, 29].
Additionally, we found that a high HBV DNA load (> 106 IU/mL) was an independent risk factor of GDM among HBsAg-positive pregnant women. A recent meta-analysis supported our finding. The latter study found that HBsAg positive had a 47% higher risk of developing GDM than HBV negative women, associated with HBV serological markers, including HBV DNA load . However, Peng et al. found that HBV infection during pregnancy was an independent risk factor for GDM, but the phenomenon is not related to viral activity such as hepatitis B e-antigen status and viral load . This phenomenon might be because HBV DNA load reflected the level of virus replication and infectivity in patients with an HBV infection. There was a strong inflammatory response in HBV-infected women with a high HBV DNA load, leading to a higher risk of GDM. Furthermore, our study showed that an HBV infection during pregnancy increases the risk of ICP (1.1% vs. 0.2%, P < 0.05) and pre-eclampsia (3.4% vs. 2.5%, P < 0.05). These findings, which have rarely been investigated before, may have important clinical implications for pregnant women [30, 31].
Given that maternal HBsAg was associated with an increased risk of adverse pregnancy outcomes, our study suggests that women should receive a serological test for HBV infection before or early in the pregnancy. Thus, it is necessary to establish appropriate diagnosis and management for HBV-infected women. We recommend that HBV DNA load and the liver function of HBsAg-positive women be monitored regularly, which might help observe any change of condition. Antiviral treatment might be considered for women with a high HBV DNA load when necessary . Moreover, the risk of adverse pregnancy outcomes in HBV-infected pregnant women should not be ignored. Screening and early interventions for GDM among high-risk populations such as those who are HBsAg positive (especially those with a high HBV DNA load), are older at maternal age, and are obese might contribute to the prevention or early diagnosis of GDM .
The strengths of the current study included a large sample size and comprehensive information on demographic characteristics, maternal and neonatal outcomes. However, our study was a single-center retrospective cohort study, which could not exclude selection and information bias. Additionally, we did not investigate the physiological mechanisms of the association between HBsAg and GDM.