Progesterone in Threatened Abortion

Inclusion Criteria: * Pregnant women attending the emergency room of the study sites with the following characteristics: * Able and willing to sign the Subject Informed Consent Form and adhere to the study visit schedule; * Age: 18-37 years; * BMI: 18-28 kg/m2; * Symptoms of threatened abortion (vaginal bleeding , with or without pelvic pain); * Ultrasound proof of viable singleton intrauterine pregnancy (positive foetal heart beat); * Gestation week ≥6 weeks (5 w +1d) and \<12 weeks (11 w + 1d) according to ultrasound dating (CRL); * Closed uterine cervix; * At the first case of threatened abortion in the current pregnancy. Exclusion Criteria: * Pregnancy obtained via ART treatment; * Subchorionic haematoma with \>50% placental detachment; * History of recurrent miscarriage; * Severe uterine malformations; * Known hypersensitivity to study medication; * Neoplasias (known or suspected breast or genital tract cancer); * Severe impairment of hepatic or renal function; * Use of concomitant medications that might interfere with study evaluations (other hormonal treatment or drugs affecting uterine contractility); * Active arterial or venous thromboembolism or severe thrombophlebitis, or a history of these events; * Porphyria; * A history of idiopathic jaundice, severe pruritus or pemphigoid gestationis during pregnancy; * Antiphospholipid syndrome; * Diabetes mellitus; * Known thyroid diseases or autoimmune conditions.