Low birth weight infant/Birth weight 3 g; Fetal exposure during pregnancy; This is a serious spontaneous case initially received from other health professional on 02-Jul-2019, concerning a female neonate patient.  The patient's mother was a 34-year-old, female of body weight: 94 lbs, height: 61 inches and body mass index (BMI): 17.8. The patient's mother had 2 previous preterm live births. The patient's mother did not have any history of previous birth defect and maternal/paternal history of major congenital malformation. The mother's concomitant medications included Prenatal vitamin (minerals NOS and vitamins NOS) for pregnancy.   The mother's last menstrual period (LMP) date was 05-Aug-2018. The type of pregnancy was singleton. The patient's mother did not consume alcohol or illicit-drugs during pregnancy but did consume tobacco (more than a cigarette per day) during pregnancy.  On 16-Oct-2018, approximately at gestational age of 10 weeks, the patient's mother was administered Flu Vaccine Cell Subunit QIV NVD (influenza vaccine, subunit influenza virus vaccine polyvalent, batch number: 252664, dose, route of administration, anatomical location and expiry date: not reported) for an unknown indication and the foetus was exposed to Flu Vaccine Cell Subunit QIV NVD via transplacental route (explicitly coded as foetal exposure during pregnancy).  On 22-Oct-2018, the mother was noted to have bacterial vaginosis and was treated with Metrogel (metronidazole, 0.75 percent twice daily vaginally; from 22-Oct-2018 to 02-Nov-2018) for bacterial vaginosis. On 25-Oct-2018, the mother experienced constipation and was given Colace (docusate sodium, 1 tablet twice daily orally; from 25-Oct-2018 and continued) for constipation. On the same day, the mother underwent ultrasound scan and no congenital malformation was reported. On 02-Nov-2018, the mother recovered from bacterial vaginosis. On 30-Nov-2018, the mother underwent Q natal screening test and no congenital malformation was reported. On 06-Dec-2018, the mother was diagnosed with yeast infection (reported as yeast) and was treated with Terzaol (tetraconazole, 4 percent cream daily vaginally; from 06-Dec-2018 to 15-Dec-2018) for yeast infection. On 15-Dec-2018, the mother had recovered from yeast infection. On an unspecified date, the mother experienced preterm labor and was given Makena (hydroxyprogesterone caproate, 250 mg intramuscular, weekly once; from 20-Dec-2018 to 09-May-2019) as treatment. On the same day, the mother underwent ultrasound scan and alpha fetoprotein (reported as alpha retoprotein) test and no congenital malformation was reported. On 11-Apr-2019, 24-Apr-2019 and on 15-May-2019, the mother underwent ultrasound scan and no congenital malformation was reported. On an unspecified after vaccination, the mother was diagnosed with herpes simplex type I and II IgG (HSV).  On 31-May-2019, at gestational age of 39.4 weeks the mother delivered a female infant through vaginal delivery and no pregnancy complications were observed. The birth weight of the infant was 3 g (as reported; coded as low birth weight baby), head circumference was 33 cm and length was 49.5 cm. Appearance, pulse, grimace, activity and respiration (APGAR) score at one minute was 9, at five minutes was 9 and no data was reported for APGAR score at ten minutes. No major congenital malformation was identified at birth.   The mother's estimated delivery date (EDD) and corrected estimated delivery date (CEDD) was reported as 04-Jun-2019.  This case is linked to case ID 201904087 (parent-child link).; Reporter's Comments: A female neonate of unspecified age was delivered vaginally at 39.4 weeks and was considered as low birth weight baby, after administration of Flucelvax QIV vaccine given at 10 weeks of gestational age (explicitly coded as exposure during pregnancy). Considering the unlikely temporal relationship between vaccination and reported event and risk factors (smoking cigarette, bacterial vaginosis treated with Metrogel, yeast infection treated with tetraconazole and diagnosis of herpes simplex type I and II), the causal role of suspect vaccine was assessed as not related. 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 of foetal exposure during pregnancy was assessed as not related considering the intended use of the vaccine. This case was assessed as serious (medically significant).