This is a serious observational study case, initially received from other health professional on 28-Mar-2019, concerning a 29-year-old, adult female pregnant subject of body weight: 147 lbs, height: 64 inches and body mass index (BMI): 25.2) 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 had no maternal and paternal history of major congenital malformations. The subject had no history of offspring with major congenital malformations. The subject had two previous elective abortions. The subject did not use tobacco, alcohol or illicit drugs during pregnancy. The subject's concomitant medication included OB complete one (iron-folic acid-Dha-fish) for healthy pregnancy (since 24-Sep-2018). The subject's last menstrual period (LMP) date was 14-Aug-2018. The type of pregnancy was singleton. On 08-Oct-2018, at the gestational age of 8 weeks, the subject received Flu Vaccine Cell Subunit QIV NVD (influenza vaccine, subunit influenza virus vaccine polyvalent, cell-culture-derived, batch number: 252232, dose, frequency, route of administration, anatomical location, and expiry date: not reported) (explicitly coded as vaccine exposure during pregnancy) for an unknown indication. On 05-Nov-2018, the subject had undergone cystic fibrosis mutation analysis, first trimester screening and no major congenital malformations were noted. On 03-Dec-2018, the subject had undergone second trimester screen and no major congenital malformations were noted. Since 28-Feb-2019, the subject had A1 diabetes mellitus (gestational diabetes mellitus). On an unspecified date, after vaccination, the subject went to emergency department with flu and fever. Unspecified test was performed which confirmed Flu. The subject was prescribed with Tamiflu (oseltamivir phosphate, 75 mg, bid, orally, from 03-Mar-2019 to 08-Mar-2019) for flu and Tylenol (paracetamol, 325 mg, every 6 hours, orally, from 03-Mar-2019 to 10-Mar-2019) for fever from emergency department. The subject gave live birth to a male neonate at the gestational age of 36.1 weeks (considered as preterm delivery) via vaginal method of delivery. The characteristics of the neonate included birth weight: 2693 grams, head circumference: 33 cm, length: 47 cm and APGAR (appearance, pulse, grimace, activity, and respiration) scores were 9 (at one minute and five minute). No major congenital malformations (MCMs) were identified at birth. The subject's estimated delivery date (EDD) was reported as 21-May-2019. The outcome of the events (flu and fever) was not reported and the event gestational diabetes mellitus was not recovered (ongoing). Follow up received from the investigator on 02-May-2019: Added pregnancy outcome details (pregnancy outcome: live birth, gestational age at outcome: 36.1 weeks, delivery method: vaginal) and infant characteristics (gender: male, birth weight: 2693 grams, head circumference: 33 cm, length: 47 cm and APGAR scores: 9 (at one minute and five minutes) in the tab. Added new events gestational diabetes mellitus and preterm delivery in the event tab. No major congenital malformations were identified at birth. The narrative was amended accordingly.; Reporter's Comments: A 29-year-old pregnant subject experienced influenza, unspecified period after receipt of Flu Vaccine Cell Subunit QIV at 8 weeks of gestation (considered as vaccine exposure during pregnancy). Due to the lack of information important for the causality assessment, such as onset latency between the vaccination and reported event influenza, company assessed the causality as unassessable. The event vaccine exposure during pregnancy assessed as not related considering the intended use of the vaccine. The patient also experienced gestational diabetes, 4 months 20 days post vaccination and preterm delivery, 6 months 16 days post vaccination. The pregnancy state and mid trimester pregnancy provide more plausible explanation for the event gestational diabetes, rather than study vaccine. Hence, assessed as not related. Considering the implausible temporal relationship between vaccination and reported preterm delivery, the event preterm delivery assessed as not related. Gestational diabetes is considered as confounding factor for the event preterm delivery. The case will be further assessed upon receipt of follow up information. The company assessed the case as serious (medically significant).