Recurrence of idiopathic polyhydramnios: A nationwide population study.

Abstract

Polyhydramnios occurs in approximately 1% of pregnancies, and idiopathic polyhydramnios (IPH) manifests with an unknown cause in 40–50% of all cases.1 Elucidating whether there is a recurrence risk will add to a better and more complete understanding of IPH.2 The objective of the present study was to calculate an odds ratio (OR) for recurrence of IPH in parous women and across generations. This was achieved by utilizing data from the compulsory Medical Birth Registry of Norway (MBRN), including all singleton births between 1967 and 2017 (n = 2 741 480). The midwife or physician attending the birth clinically judged the amount of amniotic fluid and reported this (oligohydramnios, normal, or polyhydramnios) in their notification to the registry. Polyhydramnios without fetal syndromes, malformations, infections, immunization, or maternal diabetes mellitus was defined as IPH. The authors linked the subsequent births of each woman, and across generations, by using unique national identification numbers. We calculated ORs (with 95% confidence intervals [CI]) and adjusted ORs (AOR) for recurrent IPH in subsequent births and across generations using multilevel logistic regression analysis. Possible confounding factors included: maternal age, body mass index, medical conditions, parity, smoking habits, year of birth, birthweight, placental weight, and sex of the neonate. The Regional Ethics Committee (2013/1484) and the registry owners provided ethical approval for the study protocol. SPSS version 26 (IBM Corp.) and MLwiN version 3.05 was used for analysis. IPH occurred in 0.6% of births and increased in incidence during the study period in question (0.4–1.1%). Women with a history of IPH in the first pregnancy had a seven-fold risk of IPH in the second pregnancy (Table 1). The OR of recurrence in subsequent births increased according to IPH status in the previous births. The OR of inter-generational recurrence was three-fold. Including the year of birth in the model attenuated the risk of recurrence, while including maternal or pregnancy factors did not significantly alter the results, and, therefore, were not included in the final model. A sensitivity-analysis, performed with Bayesian regression, suggested that recurrence of IPH was robust for unknown confounding factors. IPH tended to recur in subsequent births in a dose-response pattern according to history of IPH, and between generations, suggesting an influence of hereditary and/or sustained environmental factors in the regulation of amniotic fluid volume. Although validation studies have shown that the MBRN holds high quality data and is suitable for epidemiological research,3 the clinical variables describing amniotic fluid volume remains to be validated. The strengths of the present study are its prospective data collection, the population-based design, and essentially complete record linkage. The Medical Birth Registry of Norway for providing the datafile. The authors have no conflicts of interest. SR contributed to the study methodology, data curation, validation, manuscript drafting, review and editing of the manuscript, and study supervision. LL was responsible for the study methodology, data curation, formal analysis, drafting of the manuscript, and review and editing of the manuscript. CE contributed to the study conceptualization, methodology, formal analysis, project administration, writing of the original draft of the manuscript, and review and editing of the manuscript. All authors contributed to and approved of the version of the manuscript to be published.