This is a serious spontaneous case, initially received from other health professional on 25-Mar-2019, concerning a male neonate patient. The patient's mother was a 25-year-old who had 3 previous pregnancies reported with one full-term live birth and two spontaneous abortions. The historical condition of the patient's mother included nausea and vaginitis (on an unspecified date) and the current condition included cystic fibrosis (CF) carrier (since 07-Aug-2018). The patient's mother was a tobacco user as she had less than one pack per day and illicit drug user as she used opiates, morphine and marijuana. The concomitant medications of patient's mother included Metrogel and Flagyl [metronidazole benzoate] for vaginitis, Phenergan [promethazine] for nausea, ferrous sulfate for anemia and prenatal vitamins [minerals nos; vitamins nos]. The mother's last menstrual period (LMP) date was 03-Apr-2018. On 07-Aug-2018, the patient's mother underwent spinal muscular atrophy test and no major congenital malformation was noted. On 07-Aug-2018, the patient's mother underwent cystic fibrosis mutation analysis and CF carrier positive was noted, but with no major congenital malformations. On 10-Aug-2018, the patient's mother underwent ultrasound prenatal test and quadruple screen, but no major congenital malformation was noted. At approximately 28 weeks gestation, on 19-Oct-2018, the foetus was exposed to FLUCELVAX QIVc [route of administration: transplacental, batch number: 252664, dose, anatomical location and expiry date: not reported] (explicitly coded as fetal exposure during pregnancy) for an unknown indication. On 20-Oct-2018, 1 day after vaccination, the patient's mother developed anemia. On 05-Nov-2018, 03-Dec-2018, 12-Dec-2018 and 19-Dec-2018, the mother had an ultrasound prenatal test and no major congenital malformation was noted. 2 months and 13 days after vaccination, the mother vaginally delivered a male neonate at 36.6 weeks gestation (preterm birth). The neonate birth weight was 2540 grams, length was 45.7 cm and head circumference was 33 cm. The APGAR scores were 8 (one minute), 9 (five minutes) and there was no data for 10 minutes. There was no major congenital malformation was noted. The outcome of the event (preterm birth) was unknown. The mother's corrected expected delivery date (EDD) was 25-Jan-2019. This case is linked to 201902714 (mother case).; Reporter's Comments: A male neonate patient with mother's history (gestational history: 3 previous pregnancies reported with one full-term live birth and two spontaneous abortions; historical condition: vaginitis; current condition - cystic fibrosis carrier and anemia - diagnosed 1 day after vaccine administration to mother) was considered as preterm birth, after administration of FLUCELVAX QIVc vaccine at 28 weeks of gestation (explicitly coded as foetal exposure during pregnancy). The neonate was considered as preterm baby delivered by vaginal method at 36.6 weeks of gestation. Considering there is lack of evidence for a biological mechanism that could cause the event, maternal risk factors (significant gestational history, smoking, illicit drugs - opiates, morphine and marijuana, co-administered drugs - metronidazole benzoate, promethazine, ferrous sulfate and anemia), the event was assessed as not related to the suspect vaccine. 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 foetal exposure during pregnancy was assessed as not related considering the intended use of the vaccine. The company assessed the event (preterm birth) as serious (medically significant).