Perinatal outcomes in a subsequent pregnancy among women who have experienced recurrent miscarriage: a retrospective cohort study

STUDY QUESTION: Is a history of three or more miscarriages associated with adverse perinatal outcomes in a subsequent pregnancy? SUMMARY ANSWER: Recurrent miscarriage is associated with an increased risk of adverse perinatal outcomes, including preterm birth, very preterm birth and perinatal death, in a subsequent pregnancy. WHAT IS KNOWN ALREADY: Published data are conflicting with some studies reporting an increase in adverse perinatal outcomes in association with prior recurrent miscarriage while others report little or no increase. Large-scale population-based studies have been lacking. STUDY DESIGN, SIZE, DURATION: We performed a retrospective cohort study of 30 053 women with a singleton pregnancy who booked for antenatal care and delivery between January 2008 and July 2011. PARTICIPANTS/MATERIALS, SETTING, METHODS: All women who attended a university affiliated hospital in Ireland had a detailed obstetric history taken, recording the outcome of all previous pregnancies. We compared the obstetric and perinatal outcomes of 2030 women (6.8%) who had a history of three or more miscarriages (recurrent miscarriage) with the outcomes of 28 023 women (93.2%) who did not. Logistic regression analyses were performed, adjusting for potential confounding factors. MAIN RESULTS AND THE ROLE OF CHANCE: Women with a history of recurrent miscarriage were more likely to be obese, to have undergone assisted conception, to have had a previous perinatal death, and to be delivered by scheduled Caesarean section. Recurrent miscarriage was associated with an increased incidence of preterm birth (<37 weeks gestation, 8.1 versus 5.5%, adjOR 1.54; 95% CI 1.29-1.84), very preterm birth (<32 weeks gestation, 2.2 versus 1.2%, adjOR 1.80; 95% CI 1.28-2.53), and perinatal death (1.2 versus 0.5%, adjOR 2.66; 95% CI 1.70-4.14). The results were similar for both primary and secondary recurrent miscarriage. LIMITATIONS, REASONS FOR CAUTION: This is a retrospective cohort study and while regression analyses adjusted for potential confounding factors, residual confounding may persist. The strict definition of recurrent miscarriage is three consecutive miscarriages and while each woman in the study group had three or more miscarriages, they were only confirmed to be consecutive in the primary RM group. The affected women have not been categorized according to aetiology of recurrent miscarriage and it may be that adverse outcomes differ according to aetiological subgroup. WIDER IMPLICATIONS OF THE FINDINGS: This study highlights the need for specialist obstetric care for women who have had three or more previous miscarriages, particularly in relation to the risk of preterm delivery.