Preterm birth; Vaccine exposure during pregnancy; This is an observational study case, initially received from other health professional on 27-Nov-2019, concerning a 27-year-old, pregnant, female subject of body weight: 160 lbs, height: 63 inches and body mass index (BMI): 28.3, 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 increased BMI. The subject's concomitant medications included Prenatal (ascorbic acid, calcium, folic acid, iron, nicotinamide, pyridoxine, retinol, riboflavin, thiamine, tocopherol, vitamin b12 nos, vitamin d nos, zinc) for pregnancy.  The subject had no previously pregnancies. The subject had no history of offspring with major congenital malformation (MCM) and no relevant maternal and paternal medical history. The subject did not use tobacco, alcohol or illicit drugs during pregnancy.   The subject's last menstrual period (LMP) date was 08-Feb-2019. The type of pregnancy was singleton. The subject's estimated delivery date (EDD) was reported as 15-Nov-2019 and corrected estimated date of delivery (CEDD) was reported as 17-Nov-2019.   On 12-Apr-2019, the subject underwent ultrasound scan and MCM was noted.   On 03-May-2019, the subject underwent first trimester screen and no MCM was noted.   On 18-Oct-2019, approximately at 36 weeks of gestation, the subject was administered Flu Vaccine Cell Subunit QIV NVD (Flucelvax QIV) [influenza vaccine, subunit influenza virus vaccine polyvalent, batch number: 261226, dose: 0.5 ml, route of administration, anatomical location and expiration date: not reported] (explicitly coded as 'Vaccine exposure during pregnancy') for an influenza immunization.  four days after vaccination, at gestational age of 36.3 weeks, the subject vaginally delivered a normal, female neonate of body weight 2991 g, head circumference 34.9 cm and body length 48.3 cm. The appearance, pulse, grimace, activity, and respiration (APGAR) scores were 9 at one minute and 9 at five minutes. APGAR score was not reported for 10 minutes. There was no MCM identified at birth.  The event of 'premature delivery' is considered serious due to the criterion of medical significance, per company.  The reporter did not provide causality assessment.  This case is linked to 20190742 (correspondence baby case).  Company comment: The subject received Flucelvax at approximately 36 weeks of gestation. Four days after vaccination, at gestational age of 36.3 weeks, the subject delivered neonate, which was reported as preterm birth. Causality assessment is confounded by subject's increased BMI (28.3) and use of concomitant medications. Nevertheless, causal involvement of vaccine is not excluded, therefore the event of premature delivery is assessed as possibly related to Flucelvax. Exposure during pregnancy is assessed as unrelated to the suspect product per company's conventions.; Sender's Comments: The subject received Flucelvax at approximately 36 weeks of gestation. Four days after vaccination, at gestational age of 36.3 weeks, the subject delivered neonate, which was reported as preterm birth. Causality assessment is confounded by subject's increased BMI (28.3) and use of concomitant medications. Nevertheless, causal involvement of vaccine is not excluded, therefore the event of premature delivery is assessed as possibly related to Flucelvax. Exposure during pregnancy is assessed as unrelated to the suspect product per company's conventions.