This is a serious observational study case, initially received from other health care-professional on 26-Nov-2018, concerns a 27-year-old, adult,  female pregnant subject of body weight 96 lbs, height 60 cm and body mass index (BMI) 18.7, enrolled in, a study on pregnancy outcomes in women immunized with AFLURIA QIV, a seasonal quadrivalent vaccine, during pregnancy. The subject's historical drug included Synthroid (levothyroxine sodium) for thyroid. The subject's historical condition included thyroid (from an unspecified date to 31-Aug-2018). The subject had one previous pregnancy with full term live birth. The subject had no history of offspring with major congenital malformations. The subject had no relevant maternal and paternal medical history with major congenital malformations. The subject did not use tobacco, alcohol and illicit drugs during pregnancy. The subject's current condition included low iron (since an unspecified date). The subject's concomitant medications included OB complete one (as reported) for healthy pregnancy and Ferrous sulphate (reported ferrouSul) for low iron. The subject's last menstrual period (LMP) date was 12-Apr-2018. The type of pregnancy was singleton. On 16-Jul-2018, the subject underwent first trimester screening and no major congenital malformations were noted. On 18-Jul-2018, the subject underwent fibrosis mutation analysis and no major congenital malformations were noted. On 31-Aug-2018, the subject underwent second trimester screening and no major congenital malformations were noted. On 16-Oct-2018, at gestational age of 25-weeks (second trimester of pregnancy) the subject was administered Flu Vaccine Cell Subunit QIV NVD (influenza vaccine, batch number: 252232, dose, route of administration, anatomical location, and expiry date: not reported) (explicitly coded as vaccine exposure during pregnancy) for an unknown indication. On an unspecified date, after vaccination, the subject had preterm labour with not resulting in live birth. The subject delivered a full-term normal female infant via vaginal method of delivery. The infant's birth weight was 2280 grams, head circumference was 32.5 cm and body length was 42.5 cm. The APGAR scores were 9 (one minute) and 9 (five minutes). No other pregnancy complications and major congenital malformation (MCM) was not identified at birth. The subject's estimated delivery date (EDD) was reported as 29-Jan-2019. This case is linked to 201900959, the corresponding child report. Non-significant follow-up received from other health professional on 12-Dec-2018: The start date (01-Aug-2018) of historical condition thyroid was removed from the patient tab, as the reporter had no data of the start date of the condition. The narrative was amended accordingly. Follow-up was received from other health professional on 24-Jan-2019: The outcome of the pregnancy was provided (delivery type: vaginal, birth type: live birth, fetal outcome: normal, birth weight: 2280 grams, gender: female, head circumference: 32.5 cm, body length: 42.5 cm, APGAR scores were 9 (one minute) and 9 (five minutes)]. The narrative was amended accordingly.; Reporter's Comments: A 27-year-old pregnant female subject reported preterm labor, an unspecified period after receipt of Flu Vaccine Cell Subunit QIV NVD. The subject had unspecified thyroid disorder with treatment for one month with levothyroxine, which can be considered as risk factor. Considering the minimal information regarding onset latency between vaccination to event onset, implausible biological mechanism, the causality was assessed as not related to suspect vaccine. The event drug exposure during pregnancy was assessed as not related to suspect vaccine, considering it as intended use of the vaccine. The company assessed the event (preterm labor) as medically significant.