LAUSR

RESEARCH QUESTION What is the risk of miscarriage after a viable fetus verified on ultrasound at 6-8 weeks' gestation among women who conceive with medically assisted reproduction (MAR), stratified by type of fertility treatment? DESIGN A nationwide register-based cohort study of women identified in the Danish ART-Registry with a viable singleton pregnancy at 6-8 weeks' gestation between 2007 and 2010 (n = 10,011). Women were identified from The Danish Fetal Medicine Database (DFMD), which holds information on early (between 6-8 and 11-14 weeks) and late (between 11-14 and 22 weeks) miscarriages. The late miscarriage rate was compared with a control group of naturally conceived pregnancies with a viable fetus at 11-14 weeks' gestation from 2008 to 2010, identified in the DFMD (n = 146,932). RESULTS In the MAR1 cohort, the overall miscarriage rate was 11.8% (1091/9261) after an ultrasound verified viable pregnancy at 6-8 weeks' gestation. Most miscarriages occurred before the 11-14-week scan (1035/1091 [94.9%]). The early miscarriage rate was slightly higher in women who conceived with frozen embryo transfer compared with intrauterine insemination (IUI), corresponding to an adjusted OR of 1.31 (1.02 to 1.68). We found no significant risk associated with IVF and intracytoplasmic sperm injection compared with IUI pregnancies. The late miscarriage rate was 0.8% in women conceiving with MAR and 0.6% among controls (P = 0.013). CONCLUSIONS After adjustment for maternal characteristics, none of the fertility treatment types were associated with an increased risk of miscarriage compared with naturally conceiving women.