a huge blood clot behind the placental wall; felt a gush on the toilet and saw blood/bleeding heavily; had a hard time healing after the cesarean; arm very sore/arm hard to lift up; diarrhea; arm warm to touch; fever; body aches/arm very sore; vomiting; nausea; chills; tired; headaches; sweats; pregnant; This spontaneous retrospective pregnancy case was reported by a consumer and describes the occurrence of THROMBOSIS (a huge blood clot behind the placental wall) and HEAVY MENSTRUAL BLEEDING (felt a gush on the toilet and saw blood/bleeding heavily) in a 38-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch no. 026B21A) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     Concurrent medical conditions included Diabetes, Asthma, Polycystic ovarian syndrome, Human papilloma virus infection (had a low level infection prior to vaccination) and Lactose intolerant.    On 26-Apr-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. Last menstrual period and estimated date of delivery were not provided. On 26-Apr-2021, the patient experienced MATERNAL EXPOSURE DURING PREGNANCY (pregnant). On 27-Apr-2021, the patient experienced HYPERHIDROSIS (sweats), PAIN IN EXTREMITY (arm very sore/arm hard to lift up), DIARRHOEA (diarrhea), SKIN WARM (arm warm to touch), PYREXIA (fever), MYALGIA (body aches/arm very sore), VOMITING (vomiting), NAUSEA (nausea), CHILLS (chills), FATIGUE (tired) and HEADACHE (headaches). On 10-May-2021, the patient experienced THROMBOSIS (a huge blood clot behind the placental wall) (seriousness criteria hospitalization and medically significant) and HEAVY MENSTRUAL BLEEDING (felt a gush on the toilet and saw blood/bleeding heavily) (seriousness criteria hospitalization and medically significant). In May 2021, the patient experienced IMPAIRED HEALING (had a hard time healing after the cesarean). The patient was hospitalized on sometime in June 2021 due to HEAVY MENSTRUAL BLEEDING and THROMBOSIS. The cesarean delivery occurred in May-2021, which was reported as Premature. For neonate 1, The outcome was reported as Pre-Term Birth w Complications. Patient delivered baby girl.She was born alive and passed away after 10 minutes. The patient was treated with PARACETAMOL (TYLENOL) at an unspecified dose and frequency. On 26-Apr-2021, MATERNAL EXPOSURE DURING PREGNANCY (pregnant) had resolved. On 29-Apr-2021, PYREXIA (fever) and MYALGIA (body aches/arm very sore) had resolved. On 30-Apr-2021, PAIN IN EXTREMITY (arm very sore/arm hard to lift up) and SKIN WARM (arm warm to touch) had resolved. On 03-May-2021, HYPERHIDROSIS (sweats), DIARRHOEA (diarrhea) and CHILLS (chills) had resolved. On 10-May-2021, THROMBOSIS (a huge blood clot behind the placental wall), HEAVY MENSTRUAL BLEEDING (felt a gush on the toilet and saw blood/bleeding heavily) and FATIGUE (tired) had resolved. At the time of the report, IMPAIRED HEALING (had a hard time healing after the cesarean), VOMITING (vomiting), NAUSEA (nausea) and HEADACHE (headaches) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On 03-May-2021, Ultrasound Doppler: normal (normal) Normal.     The action taken with mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown) was unknown.       No relevant concomitant medications were reported. Treatment medication included tums.  Patient had six previous pregnancies with no issues. She was pregnant and received the first dose of the Moderna vaccine in her left arm on 26/Apr/2021, lot number 026B21A, no expiration date reported. In May/2021, she was at 26 weeks gestation. She felt a gush on the toilet and saw blood. She went to the hospital where there was found to be a huge blood clot behind the placental wall. The blood clot continued to grow, and baby's heartbeat slowed so they did an emergency cesarean section to deliver her baby girl. She was born alive but passed 10 minutes after. She had a hard time healing after the cesarean, she started bleeding heavily and went to the emergency room to be checked. She did not receive the second dose.  Company comment Based on the current available information which includes a temporal association between the use of the product and onset of the events, a causal relationship cannot be excluded. Fever, myalgia. chills, fatigue, nausea and headache are consistent with the known safety profile of mRNA-1273   Most recent FOLLOW-UP information incorporated above includes: On 28-Jul-2021: Additional information received included no new information.; Sender's Comments: Based on the current available information which includes a temporal association between the use of the product and onset of the events, a causal relationship cannot be excluded. Fever, myalgia. chills, fatigue, nausea and headache are consistent with the known safety profile of mRNA-1273