P-327 Birth factors related to Neonatal Uterine Bleeding (NUB) as predisposing factors of endometriosis later in life

Abstract Study question Are gestational age and a complicated pregnancy, due to hypertensive disorders, predisposing factors for the development of endometriosis and supporting NUB as pathogenetic factor Summary answer Preliminary results do not directly support the theory of NUB as pathogenetic factor of endometriosis. Hypertension and preeclampsia might have an association with endometriosis. What is known already 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 (EOE) EOE 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, EOE might be correlated with gestational age and may show a higher prevalence in woman born after a hypertension-related complicated pregnancy. Study design, size, duration Nationwide case-control study. Data were extracted from the Danish Health Register (update June 2024) 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 will compare the prevalence of the following parameters in both cases and controls: gestational age, hypertensive disorders diagnosed in the pregnancy of the mother i.e. pregnancy induced hypertension, preeclampsia, HELLP Participants/materials, setting, methods Cases : Daughters who were diagnosed with endometriosis. Controls : Daughters without the diagnosis endometriosis during the study period. Exposures : a) Hypertensive and or preeclamptic disorders in their mothers, and b) gestational age at birth. Methods: Relevant exposures were assessed in women with endometriosis and compared to women without having been diagnosed with endometriosis. Odds ratios were calculated for selected exposures with 95% CI. Main results and the role of chance Among 681,970 daughters born during the period 1977-1999, 14,446 (2.12%) were diagnosed with endometriosis, 47% with surgical confirmation. A significant negative correlation was seen for the parameter post term. Less daughters with endometriosis were born after the gestational age of 41 weeks (22.7% in women with and 24.7% in women without endometriosis). 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 preeclampsia 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 preeclampsia and born postterm showing a higher prevalence of daughter with endometriosis. Among endometriosis daughters born from 41 weeks, the proportion of mothers with hypertensive disorders was 3.6% and with hypertensive or preeclamptic disorders 4.8%. The corresponding percentages in daughters without endometriosis were 3.3% and 4.0%, respectively. The odds ratio for hypertensive disorders was 1.12 (95% CI 0.93-1.34) and for hypertensive or preeclamptic disorders 1.21 (1.03-1.42). Limitations, reasons for caution There is no documentation of neonatal bleeding in the national database, so no direct relation is evaluated. The database doesn't include private practice. Possibly cases of endometriosis are not included regarding the rather low prevalence of endometriosis in our patientgroup. A possible hereditary factor as confounder will be excluded soon. Wider implications of the findings In several studies a relation is mentioned between hypertension related complications in pregnancies in women with endometriosis. If there is a relation between pregnancies with hypertensive related complications and endometriosis later in life in the newborn, it might develop new ideas for (vascular?) pathogenetic paths or pathophysiological theories on endometriosis. Trial registration number No