This is a spontaneous case, initially received from other health professional on 12-Mar-2019, concerning a female neonate. The patient's mother's last menstrual period (LMP) date was 01-Jun-2018. The patient's mother had no maternal or paternal family history of major congenital malformations and did not use tobacco or alcohol during pregnancy. The patient's 26-year-old mother had used marijuana (illicit drug) during pregnancy. The mother's total number of previous pregnancies were 2 which were full-term live births and no birth defects were reported. The mother's historical condition included bladder infection (from 10-Aug-2018 to 20-Aug-2018) and chlamydia. The mother's historical drugs included Augmentin [dose: 875-125 mg, frequency: twice a day (bid), route of administration: oral, and gestational age: 9.9 weeks] for bladder infection and Azithromycin (Dose: 250 mg, frequency: as directed, route of administration: oral, and gestational age: 10.6 weeks) for chlamydia. The mother's current condition included anaemia (from 10-Aug-2018 to 06-Feb-2019) and concomitant medications included Prenatal vitamins (minerals NOS, vitamins NOS) for pregnancy and ferrous sulfate for anaemia. On 06-Aug-2018, the patient's mother had undergone fibrosis mutation analysis and spinal muscular atrophy and no major congenital malformation was noted. On 14-Aug-2018, the mother had undergone ultrasound scan no major congenital malformation was noted. On 21-Sep-2018, the mother had undergone quadruple screening and ultrasound scan no major congenital malformation was noted. On 19-Oct-2018, at gestational age of 20 weeks, the foetus was exposed to Flu Vaccine Cell Subunit QIV NVD (route of administration: transplacental, batch number: 252664, dose, anatomical location and expiry date: not reported) (explicitly coded as foetal exposure during pregnancy) for an unknown indication. On an unspecified date after vaccination, the mother's pregnancy status was collected, and no pregnancy complications were noted. On 14-Jan-2019, the mother had undergone ultrasound scan and no major congenital malformation was noted. The mother's estimated date of delivery (EDD) was reported as 08-Mar-2019. On 08-Mar-2019, 4 months and 17 days after vaccination, at the gestational age of 39.9 weeks, the mother delivered a female neonate of weight 2460 g (low birth weight), head circumference: 30.5 cm, length: 47.6 cm, Apgar score at one minute was 8 and at 5 minutes was 9 and no data at 10 minutes and delivery method: vaginal. No pregnancy complications were noted, and no major congenital malformations were noted at the time of birth. The outcome of the event low birth weight baby was not reported. This case is linked to case 201902639 (mother case).; Reporter's Comments: A female neonate patient with mother's history (gestational history: 2 full term live births; historical condition: bladder infection and chlamydia and current condition: anaemia) was considered as low birth weight baby, 4 months and 17 days after administration of FLUCELVAX QIV vaccine at 20 weeks of gestation (explicitly coded as foetal exposure during pregnancy). The neonate was considered as low birth weight baby delivered by vaginal method at 39.9 weeks of gestation. Considering there is no evidence for a biological mechanism that could cause the event, maternal risk factors, gestation history and use of marijuana, the event was assessed as not related to the suspect vaccine. The historical drugs (augmentin and azithromycin) administered during pregnancy 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 foetal exposure during pregnancy was assessed as not related considering the intended use of the vaccine.The company assessed the event 'low birth weight as serious (medically significant).