P-344 Prevalence and maternal risk factors for neonatal uterine bleeding (NUB): a possible origin of endometriosis?
Authors: Mondini I , Di Stefano G , Fornelli G , Reschini M , Casalechi M , Carullo G , Volpi M , Palermo M C , Marinello D , Viganò P , Somigliana E , Benaglia L 
Published: June 2023

Abstract

Study question
What is the prevalence and the cause of neonatal uterine bleeding, also known as “genital crisis”? Is it associated with maternal lifestyle and obstetric history?

Summary answer
The prevalence of NUB has been estimated as 29% and it seems to be correlated to some aspects of the maternal lifestyle

What is known already
NUB is considered a physiological phenomenon characterized by a menstrual-like bleeding occurring during the first days of life in female newborns, with an estimated incidence of 3-5%. It seems to be related to the reduction of steroid hormones in the baby after the separation from the maternal placenta, although, actually, some theories hypothesize NUB as a consequence of the exposure to molecular disruptors during intrauterine life. However, data regarding NUB still remain uncertain. Interestingly, recent theories assume a correlation between NUB and endometriosis onset, considering it as a consequence of the retrograde menstruation of stem cells during the genital crisis

Study design, size, duration
This is a prospective cohort study performed in a population of 105 mothers-to-be who delivered their babies at Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico of Milan between March 2022 and December 2022. Inclusion criteria were: gestation of a single female fetus, age between 18 and 42, being in healthy condition and undergoing a low-risk pregnancy. Women with endometriosis had also been included

Participants/materials, setting, methods
At the time of recruitment few days before delivery, patients were asked to fill a questionnaire regarding general clinical characteristics (BMI, smoking habits, diet). After two weeks from delivery, a follow up was performed asking them information about pregnancy outcomes (time to pregnancy, complications and type of delivery), a possible vaginal bleeding for the baby and its duration, the type of lactation (breastfeeding, formula or both) and clinical neonatal information.

Main results and the role of chance
NUB frequency was unexpectedly high. Twenty-nine percent of the babies experienced NUB with a duration of 3 days and insurgence 2 days post-partum. Among the variables analyzed, genital crisis resulted higher in newborns from women with significantly higher BMI compared to women with a lower BMI (BMI 23 vs 21.5 respectively, p&lt;0.05). Smoking during pregnancy was associated with a higher incidence of newborns with NUB (20% vs 4% in controls; p &lt; 0.05). According to the type of lactation, in newborns with genital crisis, 43% of them received maternal breastfeeding while the same type of feeding has been reported in 69% of controls (p&lt;0.05). Lastly, soy consumption by the mothers was observed only in 41% of cases of genital crisis while among mothers whose newborns did not experience NUB, 58% declared presence of soy in their diet (p&lt;0.05).

Limitations, reasons for caution
The population size is relatively small. Also, as prospective cohort study, loss of individuals at follow up and recall bias may occur

Wider implications of the findings
Collecting more information on the hormonal determinants of NUB could be useful for future studies on intrauterine life and reproductive disorders. If a link between NUB and endometriosis is confirmed, NUB might lead to the understanding of the onset of this pathological condition

Trial registration number
not applicable