a large blood clot was discovered between the uterus and amniotic sack; placenta was actively bleeding; a large amount of clear fluid mixed with blood rapidly discharged from her vagina.; Pregnancy at time of Vaccination :Yes/gestational period: 15 weeks (also reported as 16), gestation period at exposure was reported as 14 weeks; This is a spontaneous report from a contactable consumer. A 30-year-old pregnant female patient received BNT162B2 (PFIZER-BIONTECH COVID-19 VACCINE, solution for injection), via intramuscular, administered in arm left on 06Aug2021 18:00 (Lot Number: FA7484) as dose 1, single for COVID-19 immunisation. Medical history included rheumatoid arthritis, irritable bowel syndrome, gastrooesophageal reflux disease (GERD), sulfa medication allergy; all from an unknown date. Concomitant medications included hydroxychloroquine; probiotics; ascorbic acid, betacarotene, calcium sulfate, colecalciferol, cyanocobalamin, ferrous fumarate, folic acid, nicotinamide, pyridoxine hydrochloride, retinol acetate, riboflavin, thiamine mononitrate, tocopheryl acetate, zinc oxide (PRENATAL VITAMINS [ASCORBIC ACID;BETACAROTENE;CALCIUM SULFATE;COLECALCIFEROL;CYANOCOBALAMIN;FERROUS FUMARATE;FOLIC ACID;NICOTINAMIDE;PYRIDOXINE HYDROCHLORIDE;RETINOL ACETATE;RIBOFLAVIN;THIAMINE MONONITRATE;TOCOPHERYL ACETATE;ZINC OXIDE]); omeprazole; all taken for an unspecified indication, start and stop date were not reported. Reported pregnancy at time of vaccination :Yes, last menstrual date was 24Apr2021, delivery date due on 22Jan2022, gestational period: 15 weeks (also reported as 16), gestation period at exposure was reported as 14 weeks. Three days after receiving the first dose of the vaccine (09Aug2021), the patient had an ultrasound as part of a regular OB appointment where a large blood clot was discovered between the uterus and amniotic sack. This clot had not been present in any previous ultrasounds, the most recent prior to this event being was in 01Jul2021. Three more days after discovering this clot (12Aug2021), a large amount of clear fluid mixed with blood rapidly discharged from her vagina. She was physically examined shortly thereafter and, per OB recommendation, transported via ambulance to the emergency department (ED) of the nearest hospital for assumed rupture amniotic sack, significant loss of blood, and possible delivery of previable fetus. Additional ultrasounds showed that the blood clot discovered in the previous ultrasound had migrated toward opening of cervix, and the placenta was actively bleeding. She was monitored overnight. After discharge slowed to a manageable level, she was discharged the following morning. Reported that adverse event (AE) start date was 09Aug2021 and start time was 04:30 PM. It was further reported that AE resulted in doctor or other healthcare professional office/clinic visit, emergency room/department or urgent care, hospitalization, Life threatening illness (immediate risk of death from the event). The patient was hospitalized for 2 days. The patient has no COVID prior vaccination. Patient had COVID tested post vaccination, COVID test post vaccination via Nasal Swab on 12Aug2021 which resulted as negative. No other vaccine in four weeks. Therapeutic measures were taken as a result of a large blood clot was discovered between the uterus and amniotic sack, placenta was actively bleeding, a large amount of clear fluid mixed with blood rapidly discharged from her vagina, AE treatment included observation and IV fluids. The outcome of the events was not recovered.