Recurrent miscarriage: Are three miscarriages one too many? Analysis of a Scottish population-based database of 151,021 pregnancies Sohinee Bhattacharya a, *, John Townend b , Siladitya Bhattacharya c a Obstetric Epidemiology, Dugald Baird Centre for Research on Women’s Health, Aberdeen Maternity Hospital, Aberdeen AB25 2ZD, United Kingdom b MRC Laboratories Fajara, PO Box 273, Banjul, Gambia c Department of Obstetrics and Gynaecology, Aberdeen Maternity Hospital, Aberdeen AB25 2ZD, United Kingdom 1. Introduction Miscarriage is defined as the spontaneous loss of an intrauterine pregnancy before viability is reached. This is often described as pregnancy loss at less than 24 weeks of gestation or where the fetus weighs less than 500 g. Recurrent miscarriage or habitual abortion is traditionally defined as three or more consecutive miscarriages occurring in the same woman. The exact incidence of spontaneous miscarriage in a population is difficult to estimate as many women miscarry even before their pregnancy is clinically confirmed. While 15% of clinical pregnancies are said to end in miscarriage, biochemical studies indicate the proportion to be closer to 30% [1]. The incidence of recurrent miscarriage, on the other hand, is no more than 1% of all pregnancies. Stirrat [2] defined recurrent miscarriage as three or more pregnancy losses on the basis of epidemiological evidence. Since then it has been widely accepted that the condition is different from sporadic miscarriage and carries a worse prognosis in terms of future reproductive outcomes. Clinically, however, there is some justification in investigating and treating women who have two or more consecutive miscarriages as habitual or recurrent aborters, especially if they are advanced in age. Changes in societal and lifestyle factors have resulted in delayed childbirth. A recent large population-based record linkage study [3] has shown that increasing maternal age is independently associated with the incidence of miscarriage. Apart from age, past reproductive performance is an independent predictor of future pregnancy outcome. Regan et al. [4] showed that the incidence of miscarriage was 4–5 times more in women who had only had unsuccessful pregnancies compared to primigravidae or women with consistent- ly successful pregnancies. This paper attempts to model the risk of adverse pregnancy outcomes (further miscarriage or preterm delivery) in women with a history of one or more miscarriages in previous pregnancies taking into consideration maternal age [5,6] and smoking habits [7–9] – two most commonly accepted risk factors for these adverse outcomes. European Journal of Obstetrics & Gynecology and Reproductive Biology 150 (2010) 24–27 ARTICLE INFO Article history: Received 15 October 2009 Received in revised form 18 January 2010 Accepted 3 February 2010 Keywords: Miscarriage Recurrent miscarriage Preterm delivery ABSTRACT Objective: To assess the risk of further miscarriage or preterm delivery in women with a history of miscarriages in previous pregnancies, adjusting for maternal age and smoking. Study design: Retrospective cohort study using all women with first pregnancies recorded between 1950 and 2000 in the Aberdeen Maternity and Neonatal Databank.Exposure was one or more spontaneous miscarriages, while outcomes assessed were further miscarriage or preterm delivery. Results: There were 143,595 pregnancies with none, 6,577 with one, 700 with two, 115 with three and 24 with four consecutive previous miscarriages. The odds of miscarriage were greater in pregnancies following one previous miscarriage than none {adj.O.R. 1.94 (95% C.I. 1.80, 2.09)}. The risk of miscarriage following two miscarriages was greater than in pregnancies following one {adj.O.R. 1.56 (95% C.I. 1.28, 1.90)}. However, there was no further significant increase in odds of miscarriage for pregnancies following three {adj.O.R. 1.37 (95% C.I. 0.86, 2.17)} previous consecutive miscarriages. Odds of spontaneous preterm delivery were greater following one miscarriage than none {adj.O.R. 1.52 (95% C.I. 1.36, 1.69)} but no further increases in risk were seen. Conclusion: After adjusting for age and smoking, the risk of a further miscarriage increased sequentially in women who had one and two miscarriages. Three miscarriages did not increase the odds any further. One miscarriage was associated with an increased chance of spontaneous preterm delivery, but two or three miscarriages did not increase the odds any further. ß 2010 Elsevier Ireland Ltd. All rights reserved. * Corresponding author. Tel.: +44 1224 554672; fax: +44 1224 553708. E-mail address: sohinee.bhattacharya@abdn.ac.uk (S. Bhattacharya). Contents lists available at ScienceDirect European Journal of Obstetrics & Gynecology and Reproductive Biology journal homepage: www.elsevier.com/locate/ejogrb 0301-2115/$ – see front matter ß 2010 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ejogrb.2010.02.015