Neonatal Uterine Bleeding: An Underestimated Clinical Sign?

Neonatal uterine bleeding (NUB) occurs in approximately 5% of newborns and represents, similarly as menstrual bleeding, a progesterone (PG) withdrawal bleeding. While evident NUB is relatively rare, biochemical proofs of vaginal bleeding can be found in 25-61% of neonates, depending on different methods used to detect it. The anatomy of neonatal uterus (large cervix to corpus ratio) and the presence of thick mucus inside the cervical canal are considered predisposing factors for the possibility that a great number of neonatal bleedings are not clinically evident; the concept of retrograde menstruation with shedding of endometrial cells through fallopian tubes into the peritoneum is of paramount importance in the pathogenesis of endometriosis.