This is a serious observational study case initially received on 13-May-2019, concerning a 25-year-old adult female, pregnant subject, of body weight 206 lbs, height 64 inches and body mass index (BMI) 35.4, enrolled in a prospective observational safety study. The subject's obstetrical history noted that the subject had 3 previous pregnancies with 2 full term live births and one pregnancy with spontaneous abortion. No birth defects were reported. The subject had no history of offspring with major congenital malformation. Also, the subject had no maternal or paternal history with major congenital malformations. The subject did not have a prior history of use of tobacco, alcohol or illicit drugs during pregnancy. The subject's last menstrual period (LMP) date was 16-Aug-2018. The type of pregnancy was singleton. The subject's current conditions included anxiety and depressive disorder (since 16-Oct-2018), postural orthostatic tachycardia syndrome and seasonal allergies since an unspecified date. The subject's concomitant medications included WELLBUTRIN and ZOLOFT for depressive disorder and CLARITIN for seasonal allergies. On 23-Oct-2018, at 09 weeks gestation, the subject was administered Flu Vaccine Egg Split QIV CSL (batch number: YF41608, dose, route of administration, anatomical location and expiry date: not reported) for an unknown indication. On the same day (23-Oct-2018), the subject underwent ultrasound scan and no major congenital malformations were noted. On 13-Nov-2018, 21 days after vaccination, the subject experienced gestational diabetes mellitus (reported as pregestational diabetes mellitus). The subject was treated with NPH insulin [start date: 14-Nov-2018, dose: 36 units, frequency: every afternoon or evening (qpm), route of administration: subcutaneous and stop date: reported as ongoing). On 28-Mar-2019, 5 months and 5 days after vaccination, the subject developed anaemia. The outcome of the events gestational diabetes mellitus and anaemia was not recovered (reported as ongoing). The subject's estimated date of delivery (EDD) was reported as 23-May-2019. The corrected estimated date of delivery (CEDD) was 24-May-2019. Reporter's Comments: A 25-year-old pregnant subject with obstetrical history (3 previous pregnancies with 2 full term live births and one pregnancy with spontaneous abortion) and current conditions (anxiety and depressive disorder, postural orthostatic tachycardia syndrome and seasonal allergies) experienced gestational diabetes, 21 days after administration of study vaccine and anaemia 5 months and 5 days post vaccination, administered at 9 weeks of gestation. Considering the implausible temporal relationship between vaccination and reported events, significant obstetrical history, current conditions and no evidence suggesting a biological mechanism that could cause the events, the events were assessed as not related to the study vaccine. The reported events appear to be pregnancy related complications than caused by study vaccine. The concomitant drugs (bupropion hydrochloride, sertraline hydrochloride, loratadine) further confound this case. The decision to administer a vaccine during pregnancy is related to medical decision making by the mother and her physician and is not related to any property of the medication. The event of exposure during pregnancy was assessed as not related considering the intended use of the vaccine. The company assessed the event 'gestational diabetes mellitus' as serious (medically significant).