1. Statistics Iceland website http://px.hagstofa.is/pxen/pxweb/en
2. Swedish National Board of Health and Welfare Pregnancies, Deliveries and Newborn Infants: The Swedish Medical Birth Register 1973-2013. Assisted Reproduction, Treatment 1991-2012 Stockholm, Sweden National Board of Health and Welfare; December 2014
3. Mean age of mothers is on the rise: United States, 2000-2014;Mathews;NCHS Data Brief,2016
4. Advanced maternal age and the risk of cesarean birth: a systematic review;Bayrampour;Birth,2010
5. Pregnancy at very advanced maternal age: a UK population-based cohort study;Fitzpatrick;BJOG,2017