Premature delivery; Vaccine exposure during pregnancy; This is an observational study case, initially received from other health professional on 10-Oct-2019, concerning a 26-year-old, female pregnant subject of body weight: 187 lbs, height: 66.3 inches and body mass index (BMI): 30, enrolled in a prospective observational safety study.  The subject's relevant medical history included acne, bacterial vaginitis and increased BMI.   The subject's obstetrical history included one previous pregnancy with one full term live birth. 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 concomitant medications Prenatal and DHA (docosahexaenoic acid) vitamins (ascorbic acid, betacarotene, calcium carbonate, colecalciferol, docosahexaenoic acid, ferrous fumarate, folic acid, nicotinamide, pyridoxine hydrochloride, riboflavin, thiamine mononitrate, tocopheryl acetate, vitamin b12 nos, zinc oxide for pregnancy, Aczone (dapsone) for acne and metronidazole for bacterial vaginosis.   The subject's last menstrual period (LMP) date was 18-May-2019. The subject's estimated date of delivery (EDD) was reported as 22-Feb-2020 and corrected estimated date of delivery (CEDD) was reported as 18-Mar-2020. The type of pregnancy was singleton.  On 25-Jul-2019, the subject underwent ultrasound and no MCM was noted.   On 23-Sep-2019, at 18 week of gestation (calculated per LMP), the subject was administered Afluria QIV (Flu Vaccine Egg Split QIV CSL) [influenza vaccine, batch number: P100118566, dose, expiration date, route of administration, anatomical location: not reported] (explicitly coded as 'Vaccine exposure during pregnancy') for influenza immunization.  On 29-Oct-2019, the subject underwent ultrasound and no MCM was noted.   At gestational age of 36.7 weeks (as reported) the subject vaginally delivered a premature male neonate. The characteristics of neonate included birth weight: 3515 grams, head circumference: 32.5 cm and length: 49.5 cm. Appearance, pulse, grimace, activity and respiration (APGAR) score at one minute was 8, at five minutes was 9 and no data was reported for APGAR score at ten minutes. There were no pregnancy complications noted and no MCM was identified at birth.  The outcome of event premature delivery was not reported.   Per company, the event of premature delivery was considered as serious due to the criterion of medical significance.   The reporter did not provide causality assessment to Afluria QIV.  This case is linked to 202002232 (corresponding child case).  Follow up information received from other health professional on 04-Dec-2019: Laboratory data updated. Narrative amended accordingly.  Follow up information received from other health professional on 02-Mar-2020: Pregnancy outcome provided, stop date for the event ''vaccine exposure during pregnancy'' added and outcome changed from not reported to recovered, event ''preterm delivery'' added, case was upgraded to serious, removed classification ''Special Case with No AE''. Narrative was amended accordingly.  Company Comment: A pregnant subject was administered the suspect product Afluria QIV at 18 weeks of gestation. A subject experienced premature delivery five months later. Chronology is implausible. Concomitant use of metronidazole for bacterial vaginosis may have contributed to development of the event. With information available, causal role of the suspect vaccine is assessed as not related. Vaccine exposure during pregnancy is assessed as not related per company conventions.; Sender's Comments: A pregnant subject was administered the suspect product Afluria QIV at 18 weeks of gestation. A subject experienced premature delivery five months later. Chronology is implausible. Concomitant use of metronidazole for bacterial vaginosis may have contributed to development of the event. With information available, causal role of the suspect vaccine is assessed as not related. Vaccine exposure during pregnancy is assessed as not related per company conventions.