#4522 PREVALENCE OF CHRONIC KIDNEY DISEASE IN PREGNANCY: A UK POPULATION STUDY

Abstract Background and Aims Women with chronic kidney disease (CKD) are at greater risk of adverse pregnancy outcomes. Historically CKD in has been proposed to affect 3% of all pregnancies (0.13% with ‘moderate to severe’ CKD) but is based on expert opinion and numbers affected are propose to rise due to the rise of maternal obesity and age and could impact on service planning. However, there are no accurate estimates of CKD prevalence in pregnancy. This study aimed to investigate how many pregnancies may be affected by CKD, according to disease severity, in a UK population cohort. Method Routinely collected pregnancy data from three NHS Trust hospitals in Kent (UK) between 2010 and 2020 were extracted with Research Ethics Committee approval (19/LO/1242 and 18/SC/0158). Local laboratory and health care records were linked and used to identify women between 18 and 50 years of age with a confirmed eGFR measurement (Chronic Kidney Disease Epidemiology Collaboration 2009 without ethnicity correction) within two years prior to conception, and no current pregnancy recorded at the time of sampling. Baseline characteristics and prevalence of CKD at different stages were described. Results A total of 76, 755 pregnancies were recorded between 2010 and 2020, including 14,257/76,755 (18.6%) pregnancies with preconception eGFR (median eGFR 115 ml/min/1.73 m2 (IQR 21)). There were 1,184/14,257 (8.3%) pregnancies with a preconception eGFR <90ml/min/1.73 m2, including eGFR between 60-89 ml/min/1.73 m2 (1170 /14,257, 8.2%). Only 12/14,257 (0.08%) of pregnancies had an eGFR 30-59 ml/min/1.73 m2 and two pregnancies (0.01%) had an eGFR between eGFR 15-29 ml/min/1.73 m2. There were no pregnancies in the cohort with an eGFR <15 ml/min/1.73 m2. The cohort was majority White ethnicity (12911/13790; 94%) with 6.4% (879/13790) from Black, Asian, Mixed and East Asian ethnicities. Women with pregnancies that were affected with CKD were significantly older at conception (27, SD 5.5, vs 30.8, SD 5.5, p <0.001) and had greater prevalence of chronic hypertension (8.6% vs 11.3%, p = 0.013). Considering the whole cohort, including those without kidney function testing, the proportion of pregnancies affected by CKD was low (1,185/76,755; 1.5%). Conclusion This is the largest cohort reporting the prevalence of CKD including severity in pregnancies in the UK. Overall the total number of pregnancies affected by CKD was lower than previous estimates, especially for those with advanced disease. This finding may represent reduced fertility in women with CKD, individual decisions not to conceive, negative advice from clinicians or obstetric management at different centres not captured in this cohort. However, only 1 in 5 women prior to pregnancy had an eGFR and gestational changes in creatinine may mask identification of CKD in pregnancy. A further limitation includes only eGFR measurement prior to pregnancy was used thus women with temporary eGFR reduction may have been incorrectly included in the CKD cohort. Finally there were few women from ethnic minority groups who are disproportionately affected by CKD. Further information regarding kidney function in women of reproductive age and at conception is needed to enable true estimated of CKD prevalence in obstetric care.