vaccine exposure during pregnancy; This spontaneous prospective pregnancy case was reported by a nurse (subsequently medically confirmed) and describes the occurrence of HYDRONEPHROSIS (Hydronephrosis on one kidney) in a 37-year-old female patient (gravida 4, para 3) who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 025J20A and 013L20A) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     The patient's past medical history included Alcohol use (2 drinks/week) on 30-Oct-2020. Concomitant products included 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] for an unknown indication.   On 06-Jan-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On 03-Feb-2021 at 4:45 PM, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) dosage was changed to 1 dosage form. The patient's last menstrual period was on 02-Oct-2020 and the estimated date of delivery was 09-Jul-2021. On 06-Jan-2021, the patient experienced EXPOSURE DURING PREGNANCY (vaccine exposure during pregnancy). On 08-Feb-2021, the patient experienced HYDRONEPHROSIS (Hydronephrosis on one kidney) (seriousness criterion medically significant). The patient received mRNA-1273 (Moderna COVID-19 Vaccine) beginning around the  third month of the pregnancy. The patient gave birth to 3 neonates.  For neonate 1, the vaginal delivery occurred on 06-Jun-2019, which was reported as Full-term. The outcome was reported as Term Birth w/o Complications. syndactyly, vaginal delivery. For neonate 2, the vaginal delivery occurred on 09-Feb-2017, which was reported as Full-term. The outcome was reported as Term Birth w/o Complications. syndactyly, vaginal delivery. For neonate 3, the cesarean delivery occurred on 11-Feb-2015, which was reported as Full-term. The outcome was reported as Term Birth w/o Complications. syndactyly, polydactyly, breech (C-section). On 06-Jan-2021, EXPOSURE DURING PREGNANCY (vaccine exposure during pregnancy) had resolved. At the time of the report, HYDRONEPHROSIS (Hydronephrosis on one kidney) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On 03-Nov-2020, Pregnancy test: Positive. On 22-Dec-2020, Ultrasound abdomen: normal. On 08-Feb-2021, Ultrasound abdomen: (normal) Normal, measuring on small side but within normal range. On 08-Apr-2021, Ultrasound abdomen: (Inconclusive) hydro nephrosis on one kidney (not seen on anatomy scan so probably nothing).     For mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular), the reporter did not provide any causality assessments.   Event Hydro nephrosis was seen in ultrasound, but not seen on anatomy scan so probably nothing.  Treatment information was not provided.   Most recent FOLLOW-UP information incorporated above includes: On 20-Apr-2021: Follow up received on 20 Apr 2021, Patient's initials and history were updated.  Concomitant drug was added. Lab details were updated. Significant, Pregnancy details provided, additional event hydro nephrosis updated.; Reporter's Comments: This is a case of product exposure during pregnancy with no associated AEs for this female patient. Patient will continue to be contacted for further monitoring of AEs during the pregnancy.; Sender's Comments: Based on current available information and the temporal association between product use and the start date of the event a causal relationship cannot be excluded.