This is a serious observational study case, initially received from other health professional on 25-Mar-2019, concerning a 25-year-old adult female pregnant subject of body weight 136 lbs, height 63 inches and body mass index (BMI) 24.1, enrolled in a prospective observational safety study on pregnancy outcomes in women immunized with seasonal cell culture influenza trivalent (TIVc) or quadrivalent (QIVc) vaccine during pregnancy. The subject had three previous pregnancies that included 1 preterm live birth and 2 spontaneous abortions, and no birth defects were reported. The subject did not have a history of offspring with major congenital malformation. On an unknown date, the subject's family history of major congenital malformation was collected, and the subject had no maternal or paternal history with major congenital malformations. The subject's last menstrual period (LMP) date was 03-Apr-2018. On 07-Aug-2018, the subject underwent spinal muscular atrophy test and cystic fibrosis mutation analysis (reporter as CF Carrier) and no major congenital malformation was noted. On 10-Aug-2018, the subject underwent ultrasound and quadruple screen test and no major congenital malformation was noted. The subject's medical history included vaginitis (from 17-Aug-2018 to 24-Aug-2018) for which she received Metrogel (metronidazole) (start date: 17-Aug-2018, stop date: 24-Aug-2018). The subject's current conditions included nausea (from 17-Aug-2018 to 24-Aug-2018) and was cystic fibrosis (CF) carrier. The subject's historical drug included Flagyl (metronidazole) (start date: 28-Sep-2018, stop date: 03-Oct-2018) for vaginitis. The subject's concomitant medications included Phenergan (promethazine) for nausea and Prenatal vitamins (minerals nos, vitamins nos) for pregnancy. The subject did not use alcohol during pregnancy. The subject used tobacco during pregnancy that included smoking cigarettes less than 1 packet per day (ppd) and was still smoking it. The subject used illicit drugs during pregnancy that included opiates, morphine and marijuana however the amount consumed per day was unknown. On an unknown date, the pregnancy status of the subject was collected, and no pregnancy complications were noted. The type of pregnancy was singleton. On an unknown date, the subject stopped using the illicit drugs. On 19-Oct-2018, at 28 weeks of gestation, the pregnant subject was administered Flu Vaccine Cell Subunit QIV NVD (influenza vaccine, subunit influenza virus vaccine polyvalent, batch number: 252664, dose, route of administration, expiry date and anatomical location: not reported) (explicitly coded as vaccine exposure during pregnancy) for an unknown indication. On 20-Oct-2018, one day, after the administration of vaccine, the subject experienced anemia. On 05-Nov-2018, 03-Dec-2018, 12-Dec-2018 and 19-Dec-2018 the subject underwent ultrasound scans and no major congenital malformations were noted. 2 months and 13 days after vaccination, the subject vaginally delivered a preterm male neonate at 36.6 weeks gestation (explicitly coded as premature labour). The neonate's birth weight was 2540 grams, head circumference was 33 cm and body length was 45.7 cm. There was no major congenital malformation identified at birth. The APGAR scores were 8 (at one minute), 9 (at five minutes) and there was no data for 10 minutes. The outcome of the event anemia was not recovered and outcome of the event premature labour was not reported. The subject's estimated delivery date (EDD) was reported as 08-Jan-2019 and corrected estimated delivery date (CEDD) was reported as 25-Jan-2019. This case is linked to case 201902713 (baby case).; Reporter's Comments: A 25-year-old pregnant subject was diagnosed with anaemia, 1 day after receipt of Flu Vaccine Cell Subunit QIV (considered as vaccine exposure during pregnancy). The patient also experienced premature labour, 2 months 13 days post vaccination at 36.6 weeks of gestation. Considering the implausible temporal relationship, the event anaemia assessed as not related to study vaccine. The maternal past obstetrical history (1 preterm birth and 2 spontaneous abortions), use of tobacco, illicit drugs like opiates, morphine and marijuana (known risk factors) and the event anaemia, provide more plausible explanation of the event premature labour, rather than the study vaccine. Hence, sponsor assessed the event premature labour as not related. The event vaccine exposure during pregnancy assessed as not related considering the intended use of the vaccine. The company assessed this case as serious (medically significant).