Gestational diabetes mellitus; Vaccine exposure during pregnancy; This is an observational study case, initially received from other health professional on 16-Jul-2020, concerning a 32-year-old female, pregnant subject of body weight: 252 lbs, height: 62.4 inches and body mass index (BMI): 45.5, who was enrolled in, a prospective observational safety study on pregnancy outcomes in women immunized with seasonal cell culture influenza trivalent (TIVc) or quadrivalent (QIVc) vaccine during pregnancy.  The subject's medical history included Caesarean (on 18-Oct-2014) and obesity.  The subject's concomitant medications included Prenatal vitamins (unspecified minerals and vitamins) and M-Natal plus iron (vitamin A, vitamin C, vitamin D, vitamin E, thiamine, riboflavin, niacin, vitamin B6, folic acid, vitamin B12, calcium, iron, zinc, copper), both as obstetric (OB) supplements and Tdap (diphtheria vaccine toxoid, pertussis vaccine acellular, tetanus vaccine toxoid) as vaccine.  The subject's obstetrical history included one previous pregnancy with full term live birth. The subject had no history of offspring with major congenital malformation (MCM), nor relevant maternal or paternal history. The subject did not consume tobacco, alcohol or illicit drugs during pregnancy.  The subject's last menstrual period (LMP) was 12-Jul-2019. The subject's estimated delivery date (EDD) was reported as 17-Apr-2020 and corrected EDD (CEDD) was reported reported as 25-Apr-2020. The type of pregnancy was singleton.  On 26-Sep-2019, at gestational age of 10 weeks (calculated per LMP), the subject received Flucelvax QIV (Flu Vaccine Cell Subunit QIV NVD) [influenza vaccine, subunit influenza virus vaccine polyvalent, dose: 0.5 ml, batch number: 261207, route of administration, anatomical location and expiry date: not reported] (explicitly coded as Vaccine exposure during pregnancy') for influenza immunisation.  On 15-Oct-2019, the subject underwent nuchal translucency and first trimester screen. No MCM was noted.  On 12-Nov-2019, the subject underwent second trimester screen and maternal serum alpha-foetoprotein  (MSAFP / serum markers). No MCM was noted.  On 04-Dec-2019, the subject underwent anatomy ultrasound and no MCM was noted.  On 12-Feb-2020, 4 months 17 days after vaccination, the subject developed gestational diabetes mellitus and started treatment for it with two tablets of metformin, administered orally, twice a day, and with Lantus U-100 (Insulin glargine) at a dose of 40 units, administered subcutaneously.  On 06-Mar-2020, 5 months and 9 days after vaccination, oligohydramnios was noted.  On an unknown date, an unknown amount of time after vaccination, non-reassuring foetal heart rate tracing was noted.  At gestational age of 38.71 weeks (as reported), the subject delivered a male neonate by caesarean method. The birth weight of the neonate was 3402g. No data for head circumference and length was provided. Appearance, pulse, grimace, activity and respiration (APGAR) score at one minute was 8 and at five minutes was 9. APGAR score at ten minutes was not provided. No MCM was identified at birth. On the same day, the neonate recovered from oligohydramnios.  At the time of initial reporting, the subject did not recover from gestational diabetes mellitus.  Per company, the event of gestational diabetes mellitus was considered serious due to criterion of medical significance.  The reporter did not provide a causality assessment to Flucelvax QIV.  This case is linked to case 202003896 (the corresponding child case).  Company comment: A 32-year-old pregnant subject was administered Flucelvax QIVc at gestational age of 10 weeks. The subject developed gestational diabetes mellitus, four months and 17 days after vaccination. Causality was highly confounded by medical history obesity. Causal role of the suspect vaccine is assessed as not related, due to mentioned confounder, biological implausibility and unsuggestive chronology. Vaccine exposure during pregnancy is not related per company's conventions.; Sender's Comments: A 32-year-old pregnant subject was administered Flucelvax QIVc at gestational age of 10 weeks. The subject developed gestational diabetes mellitus, four months and 17 days after vaccination. Causality was highly confounded by medical history obesity. Causal role of the suspect vaccine is assessed as not related, due to mentioned confounder, biological implausibility and unsuggestive chronology. Vaccine exposure during pregnancy is not related per company's conventions.