Background: Adverse prior pregnancy outcomes influences the chance of live birth in the next pregnancy and increasing maternal age decreases chance of live birth. However, no prior studies have taken each woman’s exact pregnancy history into account.

Aims: 1) How does the sequence of prior pregnancy events, obstetric complications and maternal age affect chance of live birth in the next pregnancy; 2) Are prior pregnancies predictive for the outcome?

Materials and methods: Nationwide, registry-based cohort study of all women living in Denmark from 1977 to 2017 (n=1 285 230) with at least one pregnancy in either the Danish Medical Birth Registry or the Danish National Patient Registry (n= 2 722 441 pregnancies). Data were analysed using logistic regression with a robust covariance model to account for women with more than one pregnancy. Model discrimination and calibration were ascertained using 20% of the women in the cohort randomly selected as an internal validation set.

Main results and the role of chance: Obstetric complications, still birth, ectopic pregnancies and pregnancy losses had a negative effect on the chance of live birth in the next pregnancy. Consecutive, identical pregnancy outcomes (pregnancy losses, live births or ectopic pregnancies) immediately preceding the next pregnancy had a larger impact than the total number of any outcome. Model discrimination was modest (C-index = 0.60, positive predictive value = 0.45), but the models were well calibrated.

Discussion: Prior pregnancy history has a significant impact on the chance of live birth in the next pregnancy. However, the results emphasize that only taking age and number of losses into account does not predict if a pregnancy will end as a live birth or not. A better understanding of biological determinants for pregnancy outcomes is urgently needed.

Funding: The work was supported by the Novo Nordisk Foundation, Ole Kirk Foundation and Rigshospitalet's Research Foundation.

Biography: Dr Kolte is a medical doctor from University of Copenhagen from 2009 and holds a PhD from the same university from 2016. The title of the thesis was “Recurrent Pregnancy Loss – a family affair | Studies of genetics, epidemiology and evolution”. Since 2019 she has been an assistant professor at the Dept. Clinical Medicine, University of Copenhagen. Currently, she is an OBGYN resident at North Zealand Hospital. She has been involved in research since the early 2000’s and she has worked extensively on different aspects of pregnancy complications, especially recurrent pregnancy loss. She has published 32 peer-reviewed papers, participated in the ESHRE guideline on recurrent pregnancy loss from 2017 and have co-authored several book chapters. Her scientific works include studies on evolution, immunology, mental health, endocrinology and epidemiology.