Since essential factors have changed in recent years in assisted reproduction technologies (ARTs), this study reassessed the association between ART and
breech presentation. We primarily aimed to estimate the correlation between ART and breech at delivery. Secondary purposes were to evaluate the correlation between other
subfertility treatments (OSTs) and breech and to assess possible confounding factors and temporal trends. This study investigated the 31,692,729 live birth certificates from US states and territories in the 2009-2020 period. The inclusion criteria were singleton births reporting the method of conception and the presentation at delivery. The outcome was the
breech presentation at delivery, while the primary exposure was ART, the secondary exposure was OST, and the potential confounding factors from the literature were considered. ART (OR 2.32 CI.95 2.23-2.41) and OST (OR 1.79 CI.95 1.71-1.87) were independent and significant risk factors for breech at delivery (p < 0.001). This study confirmed
breech presentation risk factors maternal age, nulliparity, tobacco
smoke, a previous cesarean delivery (CD), neonatal female sex, gestational age, and
birth weight. Black race and Hispanic origin were verified to be protective factors. We found breech prevalence among ART and OST to be stable during the study period. Meanwhile, newborn
birth weight was increased, and the gap between breech and other presentations in ART was reduced. Our results indicate that singleton pregnancies conceived by ART or OST were associated with a higher risk of breech at delivery. Well-known risk factors for the
breech presentation were also confirmed. Some of these factors can be modified by implementing interventions to reduce their prevalence (e.g., tobacco
smoke and previous CD).