Inclusion Criteria:  Minimum age of 18 Women with placenta previa or low-lying placenta confirmed by TVS at 19-23 6/7 weeks of gestation.  Women attending Maternity Triage with vaginal bleeding at < 32 weeks of gestation, with a diagnosis of placenta previa or low-lying placenta and not requiring an emergency delivery.  Women with a normally located placenta at the II trimester ultrasound scan, at 19-23 6/7 week of gestation (control group) Single pregnancy Signature of the informed consent to participate in the study  Note: Women of the "control group" will be recruited in a 1:3 ratio. After the inclusion of 1 case, 3 women with a normally located placenta will be recruited, according to the parity of the woman representing the case (e.g.: 1 CASE= nulliparous woman, 3 CONTROLS= 3 nulliparous women).  Exclusion Criteria:  Suspected or confirmed invasive placentation (i.e., placenta accreta) Vaginal bleeding requiring emergency delivery Inability to meet the conditions set out in the study protocol