This search was conducted using the following keywords: (“gestational diabetes mellitus”) AND (“COVID-19” OR “coronavirus” OR “SARS-CoV-2”). Medical Subject Headings (MeSH) and Embase Subject Headings terms as well as title/abstract terms were searched. In addition, we manually searched reference lists.

This search was conducted using the following keywords: (“gestational diabetes mellitus”) AND (“telemedicine” OR “telemonitoring” OR “telemetry” OR “mHealth” OR “mobile applications” OR “smartphone”). MeSH and Embase Subject Headings terms as well as title/abstract terms were searched. In addition, we manually searched reference lists.

Studies that met the following inclusion criteria were selected: peer-reviewed; published in English or German; observational, cohort, and clinical studies, case reports/series, letters, and comments reporting maternal, fetal, and neonatal outcomes in pregnant women with GDM and COVID-19.

Because COVID-19 emerged at the end of 2019 and is still quite unexplored, especially for special target groups such as patients with GDM, few studies are available to date. We therefore considered various study designs (including case reports and letters) and included all papers that reported on patients with COVID-19 and GDM, even if GDM was not explicitly the focus of the respective paper. Furthermore, we did not impose any restrictions on maternal, fetal, or neonatal outcomes.

Articles that met the following inclusion criteria were selected: peer-reviewed; published in English or German; clinical controlled trials (CCTs) and randomized controlled trials (RCTs) examining telemedical treatment for pregnant women with GDM and reporting on the maternal outcomes of HbA_1c, FBG, or RBG.

Telemetry was defined as remote recording and transmission of patient data via a telecommunications system to a health care provider to provide clinical support and improve health outcomes [23]. We included video calls, telephone calls, internet/web-based platforms, and smartphone/mobile app–based interventions.

The following articles were excluded: papers that did not specify the type of diabetes, and articles that did not report maternal or offspring outcomes and focused instead on GDM screening/management/diagnosis, anxiety and stress during lockdown, or prevention of GDM.

The following articles were excluded: posters, comments, letters, study protocols, and proceedings; studies that did not specify the type of diabetes; studies that described technologies only; studies that pooled data with other technologies and other diseases; and papers focusing on GDM prevention or GDM diagnosis.

We sorted the COVID-19 studies by outcome. We divided the outcomes into maternal and offspring outcomes. Where possible, we calculated the means (Apgar score and birth weight).

We divided the telemedical studies into two groups: web-based and app-based. Web-based interventions are based on websites and the internet, with asynchronous communication between patients and health care providers. App-based interventions are based on smartphone and mobile phone apps.

We conducted a meta-analysis to determine the impact of the interventions on the HbA_1c concentration because this was the most frequently studied outcome. We used Excel (Microsoft Corporation) for pooling the data and for calculations, and we took into account all studies that provided complete information. In the calculations, we considered web-based and app-based studies. For determining the change in HbA_1c (%), we pooled appropriate studies and calculated the differences in the means, with 95% confidence intervals, for the intervention and control groups at the end of the interventions. Based on the HbA_1c mean differences and confidence intervals, we created a forest plot.

The literature search yielded 228 citations, of which 136 unique citations were screened based on title and abstract (Multimedia Appendix 2). Then, we screened 19 articles based on the full texts. We added 1 study (Blauvelt et al [29]) through manual research. Finally, we selected 16 appropriate COVID-19–related articles in this systematic review [3,5,29-42]. Of these, 11 were case reports, 3 were letters, 1 was a case series, and 1 was a retrospective single-center study. In total, 41 patients with GDM were analyzed. An overview of all included studies is provided in Multimedia Appendix 3.

Overall, the reported outcomes are very heterogeneous, and there are only a few overlaps of the same outcomes in the studies. It should also be noted that the papers are not very detailed and generally contain little information, which is related to the fact that at the beginning of the COVID-19 pandemic, papers can be published more quickly and in a simplified form.

The most common COVID-19 symptoms were fever (n=12), cough (n=13), dyspnea (n=4), shortness of breath (n=3), diarrhea (n=2), and vomiting (n=2).

In total, 22 women required cesarean deliveries, including 3 emergency cesarean deliveries. Furthermore, 5 women were admitted to the intensive care unit (ICU). Blauvelt et al [29] reported lung overdistension, hyperglycemia after antenatal corticosteroid administration, and mechanical ventilation (n=1 woman). Cooke et al [30] noticed that 1 patient experienced psychiatric sequelae postoperatively. In addition, Vlachodimitropoul et al [31] outlined a postpartum hemorrhage of 1.5 L, controlled with uterine artery ligation and B-Lynch compression alongside uterotonics and blood products (n=1 patient). Govind et al [32] reported that, following delivery, a patient continued to desaturate (80%-85%) on 100% oxygen.

Kleinwechter and Laubner [3] noted vaginal bleeding and that the patient was fever-free at day 6, with oxygen requirement declining (n=1 woman).

Moreover, Oliva et al [33] outlined that the status of the patient (fever, dyspnea, respiratory status worsening from oxygen saturation as measured by pulse oximetry [SpO₂] 95%-92%) improved rapidly post–cesarean delivery (2 hours after delivery SpO₂ to the low 90th percentile on room air, which improved to 100% on 15 L/min of oxygen) and that the cesarean delivery was uncomplicated. Uzel and Lakhno [35] found leukocytosis (19 × 103/μL) and mild anemia (hemoglobin 10.1 g/dL) in the clinical blood test (n=1 woman). Activated partial thromboplastin time, prothrombin time, and international normalized ratio were prolonged, levels of C-reactive protein (179.7 mg/L) and procalcitonin (0.15 ng/ml) were raised, and low oxygen saturation (75%) was detected. The authors reported that the patient died (35 year-old woman with obesity, lymphopenia, hyperglycemia, and trace proteinuria). D’Ambrosi et al [37] outlined that 6 women (in a retrospective single-center study) did not require ICU admission or mechanical ventilation, but 4 women underwent elective cesarean deliveries.

In addition, Fontanella et al [38] reported that there were no adverse maternal outcomes and the women left the hospital after 5 days because of rapid improvement. Kleinwechter et al [5] (n=21 women) showed 2 admissions to the ICU, and in 4 cases, the women received symptomatic COVID-19–associated therapy. No invasive ventilation was required, and 56% of the cases were cesarean deliveries (9/16).

The mean Apgar score (1 minute) was 5.9 in 8 newborns [29-33,35,36,39]. In addition, the mean Apgar score (5 minutes) was 7.5 in 17 newborns (including 1 set of triplets) [29-33,35-37,39]. The birth weight [30,32-37,40,41] was between 1250 g [40] (a triplet) and 4165 g [32], whereas the mean birth weight was approximately 2621.29 g (n=17 newborns).

Blauvelt et al [29] reported that the newborn evolved respiratory distress syndrome and laboratory test results showed leukopenia, neutropenia, lymphopenia, mild acidosis, and normal lactate. A SARS-CoV-2 test was negative, and at 16 days of life, the neonate was clinically stable on high-flow nasal cannula at 3 L/min and 21% fraction of inspired oxygen (FiO₂). Govind et al [32] observed viral pneumonia on day 6, but the newborn recovered well and was ventilated for 10 days.

Moreover, Oliva et al [33], Uzel and Lakhno [35], Majachani et al [39] and Rabiei et al [40] noted admissions to the neonatal intensive care unit (NICU) (n=6 newborns). In total, 2 newborns needed supplement oxygen [32,33]. Additionally, 7 children tested negative for COVID-19 after their births [29,35,36,40,41], and 1 had a positive nasopharyngeal swab after 24 hours. Pulinx et al [42] reported the death of 2 fetuses (twins). Cooke et al [30] and Fontanella et al [38] observed no adverse neonatal outcomes.

The literature search yielded 408 citations, of which 348 unique citations were screened based on title and abstract (Multimedia Appendix 3). Then, we screened 14 articles based on the full texts. Finally, we selected 9 appropriate telemedicine-related articles [43-51] in this systematic review. Of these, 6 were RCTs, 2 were CCTs, and 1 was a quasi-experimental design.

In total, we analyzed 480 patients in the intervention groups and 494 in the control groups. The interventions were grouped into web-based and app-based interventions. We did not find any video consultations, and we did not find studies that reported on the outcome of RPG. In total, we analyzed 6 web-based and 3 app-based telemedicine interventions.

The effects of the interventions based on the comparison of HbA_1c levels between the intervention and control groups at the end of the study were analyzed. Dalfra et al [47] (strong quality) and Guo et al [49] (strong quality) indicated clear and significant improvements of HbA_1c values (P<.001 [49] and P=.008 [47]). Our findings are based on 5 web-based [44-48] and 2 app-based [49,50] studies. The meta-analysis revealed a mean effect size of –0.138% (95% CI –0.24 to –0.04) for web-based interventions and –0.305% (95% CI –0.88 to 0.27) for app-based interventions.

In general, the meta-analysis demonstrated a mean difference in HbA_1c of –0.19% (95% CI 0.34 to 0.03) for all telemedical interventions (n=7). Multimedia Appendix 6 provides the forest plot and the calculations and data for the meta-analysis.

In total, 2 of 3 studies reported improvements in FBG levels by web-based interventions. Homko et al [43] (moderate quality) outlined enhancements in their intervention group compared to the control group (intervention, 91.5 [10.5] mg/dL, vs control, 94.3 [0.26] mg/dL, P=.26). In addition, Kim et al [46] (weak quality) showed lower FBGs in the intervention group (78.8 [8.4] mg/dL) compared to the control group (80.9 [8.4] mg/dL), but the difference was not significant between groups (P value not reported).

Furthermore, all app-based studies (n=2) reported clear decreases in FBG values by implementing app-based telemedicine interventions. Yang et al [51] (moderate quality) indicated that a smartphone-based telemedicine system (WeChat app) was significantly associated with an obvious improvement in FBG (intervention 4.31% (0.75) versus control 5.31% (1.29), P<.001). Moreover, Guo et al [49] (strong quality) showed improvements compared to the controls (intervention 4.9% (0.9) vs control 5.0% (0.8), P=.74).