Vaccine exposure during pregnancy; Hypothyroid; This is an observational study case, initially received from other health professional on 28-Jan-2020, concerning a 36-year-old, female pregnant subject of body weight: 138 lbs, height: 66 inches and body mass index (BMI): 22.3 enrolled in, a prospective observational safety study.  The subject's medical history included advanced maternal age.  The subject's concomitant medications were not provided.  The subject's obstetrical history included two previous pregnancies of full term live births. The subject had no offspring with major congenital malformation (MCM). The subject had not maternal family history with MCM, but subject's nephew with Down's syndrome was noted in paternal family history.  The subject's last menstrual period (LMP) date was 11-May-2019. The type of pregnancy was singleton. The subject's estimated delivery date (EDD) was 15-Feb-2020 and corrected estimated delivery date (CEDD) was 20-Feb-2020. The subject did not consume tobacco, alcohol and illicit-drugs during pregnancy.  On 08-Jul-2019, the subject performed ultrasound and no MCM was noted.  On 15-Jul-2019, the subject performed first trimester screen and no MCM was noted.  On 09-Oct-2019, the subject performed ultrasound and no MCM was noted.  On 06-Nov-2019, at gestational age of 25 weeks, the subject was administered Flucelvax QIV (Flu Vaccine Cell Subunit QIV NVD) (influenza vaccine, subunit influenza virus vaccine polyvalent, batch number: 261207, dose, route of administration, anatomical location and expiry date: not reported) (explicitly coded as Vaccine exposure during pregnancy') for influenza immunisation.  On an unspecified date in 2019, the patient developed hypothyroidism (reported as hypothyroid').  At the time of this report, the outcome of hypothyroidism was not resolved.  Per company, the event of hypothyroidism was considered serious due to the criterion of medical significance.  The reporter did not provide causality assessment to Flucelvax QIV.  Company comment: A 36-year-old female pregnant subject developed hypothyroidism after vaccination with the suspect product Flu Vaccine Cell Subunit QIV NVD for influenza immunisation. Reportedly, on an unspecified date in 2019, the patient developed hypothyroidism. Chronology needs more clarification. The subject's medical history included advanced maternal age and concomitant medications were not provided. Hypothyroidism, also called underactive thyroid or low thyroid, is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormone. Hypothyroidism may be due to a number of factors, including: autoimmune disease (Hashimoto's thyroiditis), over-response to hyperthyroidism treatment, thyroid surgery, radiation therapy, medications, congenital diseases, pituitary disorder, pregnancy. Some women develop hypothyroidism during or after pregnancy (postpartum hypothyroidism), often because they produce antibodies to their own thyroid gland. Left untreated, hypothyroidism increases the risk of miscarriage, premature delivery and preeclampsia  a condition that causes a significant rise in a woman's blood pressure during the last three months of pregnancy. It can also seriously affect the developing foetus and iodine deficiency. Considering provided information, causality is assessed as not related for both events. (Exposure during pregnancy is not related per company conventions.); Sender's Comments: A 36-year-old female pregnant subject developed hypothyroidism after vaccination with the suspect product Flu Vaccine Cell Subunit QIV NVD for influenza immunisation. Reportedly, on an unspecified date in 2019, the patient developed hypothyroidism. Chronology needs more clarification. The subject's medical history included advanced maternal age and concomitant medications were not provided. Hypothyroidism, also called underactive thyroid or low thyroid, is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormone. Hypothyroidism may be due to a number of factors, including: autoimmune disease (Hashimoto's thyroiditis), over-response to hyperthyroidism treatment, thyroid surgery, radiation therapy, medications, congenital diseases, pituitary disorder, pregnancy. Some women develop hypothyroidism during or after pregnancy (postpartum hypothyroidism), often because they produce antibodies to their own thyroid gland. Left untreated, hypothyroidism increases the risk of miscarriage, premature delivery and preeclampsia  a condition that causes a significant rise in a woman's blood pressure during the last three months of pregnancy. It can also seriously affect the developing foetus and iodine deficiency. Considering provided information, causality is assessed as not related for both events. (Exposure during pregnancy is not related per company conventions.)