Polyhydramnios; Preterm birth at 34 weeks of gestational age; Low birth weight of 2410 g; Foetal exposure during pregnancy; This is an observational study case, initially received from other health professional on 25-Jun-2020, concerning a male foetus whose mother was a 25-year-old, pregnant, female subject of body weight: 168 lbs, height: 70 inches and body mass index (BMI): 24.1, enrolled in, a prospective observational safety study on pregnancy outcomes in women immunized with Afluria QIV, a seasonal quadrivalent vaccine, during pregnancy.  The foetus' mother's relevant medical history included gestational hypertension and pre-eclampsia with the first baby.   The foetus' mother's concomitant medications included Prenatal vitamins (unspecified vitamins and minerals) for pregnancy.  The foetus' mother's obstetrical history noted that the mother had two previous pregnancies with one full term live birth and one preterm live birth at 35 weeks with birth defect including gastroschisis. The foetus' mother had no maternal or paternal history with major congenital malformations (MCMs). Also, the foetus' mother had no history of offspring with MCM. The foetus' mother used 10 cigarettes per day during pregnancy. The foetus' mother did not use alcohol or illicit drugs during pregnancy.   The foetus' mother's last menstrual period (LMP) date was on 02-Jul-2019. The foetus' mother's estimated delivery date (EDD) was reported as 07-Apr-2020, while corrected estimated date of delivery (CEDD) was not reported. The type of pregnancy was multiple (twin gestation).   On 27-Aug-2019, the foetus' mother underwent ultrasound and no MCMs were noted.   On 25-Sep-2019, the foetus' mother underwent non-invasive prenatal testing (NIPT) and nuchal translucency, and no MCMs were noted.  On 23-Oct-2019, the foetus' mother underwent maternal serum alpha fetoprotein screening (MSAFP) and no MCMs were noted.  On 19-Nov-2019, at approximately 20 weeks of gestation (calculated per LMP), the foetus mother was administered Afluria QIV (Flu Vaccine Egg Split QIV CSL) [influenza vaccine; batch number: P100112488, dose, route of administration, anatomical location and expiration date: not reported] (explicitly coded as Foetal exposure during pregnancy') for an influenza immunisation.   On the same day, after vaccination, the foetus mother developed anaemia and received treatment medication ferrous sulphate at the dose of 325 mg, administered via oral route, once per day. Also, the foetus mother underwent 20-week anatomy ultrasound scan and echogenic bowel in twin A was noted. No MCMs were noted.   On an unspecified date, unknown amount of time after vaccination, the polyhydramnios in twin foetuses was noted.  On 06-Feb-2020, the twin foetuses recovered from polyhydramnios.  At 34 weeks of gestation (as reported), the foetus mother vaginally delivered a preterm birth, twin male neonates (A and B). The neonate's A birth weight was 2770 grams, while head circumference and body length were not reported. The appearance, pulse, grimace, activity and respiration (APGAR) scores were 7 at one minute and 8 at five minutes. APGAR score was not reported for 10 minutes. The neonate's B birth weight was 2410 grams, while head circumference and body length were not reported. The appearance, pulse, grimace, activity and respiration (APGAR) scores were 7 at one minute and 9 at five minutes. APGAR score was not reported for 10 minutes. There was no MCM identified at birth for twins. On the same date, the echogenic bowel in twin A was resolved.  At the time of this report, the outcome of events premature baby 33 to 36 weeks' and 'low birth weight baby' was not reported.   The events of polyhydramnios', premature baby 33 to 36 weeks' and 'low birth weight baby' were considered serious due to criterion of medical significance, per company.  The reporter did not provide causality assessment.  This case is linked to case number 202001669 (the corresponding twin A case) and 202001668 (the corresponding mother case).  Company Comment: A male foetus experienced premature birth with low birth weight, three months after foetal exposure to the suspect product, Afluria QIV. Chronology is unsuggestive. Early-onset of labour is frequent in twin pregnancies, which confound causality for low birth weight as well. Therefore, causal role of the suspect vaccine is assessed as not related for premature birth and low birth weight. The event of polyhydramnios was noted on an unknown date after vaccination. Chronology needs more clarification. Although twin pregnancy is strong confounder for polyhydramnios, due to lack of information about onset date, causality is unassessable. Foetal exposure during pregnancy is assessed as unrelated per company's conventions.; Sender's Comments: A male foetus experienced premature birth with low birth weight, three months after foetal exposure to the suspect product, Afluria QIV. Chronology is unsuggestive. Early-onset of labour is frequent in twin pregnancies, which confound causality for low birth weight as well. Therefore, causal role of the suspect vaccine is assessed as not related for premature birth and low birth weight. The event of polyhydramnios was noted on an unknown date after vaccination. Chronology needs more clarification. Although twin pregnancy is strong confounder for polyhydramnios, due to lack of information about onset date, causality is unassessable. Foetal exposure during pregnancy is assessed as unrelated per company's conventions.