(19) Birth Factors related to Endometriosis later in life in the light of Neonatal Uterine Bleeding (NUB)

Background: Sampson’s theory of Retrograde menstruation is regarded as an important origin of endometriosis but does not explain all cases of endometriosis. Especially, endometriosis occurring before and during puberty, referred to as early-onset endometriosis which might be explained by the phenomenon of neonatal uterine bleeding (NUB), as it is possibly the first retrograde menstrual bleeding and occurring around the 7th day postpartum. As NUB is more often seen in neonates born post term or after hypertension induced complicated pregnancies, endometriosis later in life might be correlated with gestational age and may show a higher prevalence in woman born after a hypertension-related complicated pregnancy.

Methods: Data were extracted from the Danish Health Register (update 2023) and the Medical Birth Register (Danish new-borns from 1977-1999). Women with and without endometriosis will be compared. Using cross-sectional and longitudinal models we compared the prevalence of the following parameters in both cases and controls: gestational age, birth weight, hypertensive disorders diagnosed in the pregnancy of the mother i.e. pregnancy induced hypertension, preeclampsia, HELLP.

Results: A total of 681970 daughters could be evaluated divided in two groups: no endometriosis (n=667524) and with endometriosis (n=14446). A significant negative correlation was seen for the parameter post term. Less daughters with endometriosis were born after the gestational age of 41 weeks. RR=0.93 (95% CI 0.90-0.96) and p< 0.001. The prevalence of daughters with and without endometriosis, born after a pregnancy with all hypertensive disorders combined was similar. RR=1,00 (95% CI 0.92-1.08) and p NS. However, in the group with only hypertension or pre-eclampsia there was a slightly higher prevalence of daughters with endometriosis. RR=1.07 (95% CI 1.00-1.15) p=0.0495. This difference was even more clear in the group with hypertension or pre-eclampsia and born postterm showing a higher prevalence of daughters with endometriosis. RR = 1.19 (95% CI 1.02-1.39) p=0.03. These are preliminary results and a full evaluation of the groups is in progress at the moment.

Conclusions: Preliminary results not directly support the theory of NUB as an origin of endometriosis later in life. Hypertension and preeclampsia might have an association with endometriosis.