A recent study evaluated the role of routine ultrasound scans at 35+0 to 36+6 weeks of gestation in detecting abnormal fetal presentations and their outcomes.

Researchers analyzed data from 107,875 singleton pregnancies, revealing critical insights into fetal positioning, external cephalic version (ECV) attempts, and spontaneous rotation. Their findings were published in Obstetrics & Gynaecology. 

At the 36-week scan, 94.2% of fetuses presented as cephalic, while 5.8% exhibited breech, transverse, or oblique presentations. Among the 6,211 cases of noncephalic presentation, ECV was attempted in 1,584 cases (25.5%) and was successful in 44.1% of attempts. In 5,513 cases where ECV was not attempted or unsuccessful, 37.7% of fetuses exhibited spontaneous rotation to a cephalic presentation.

"In 74.8% [of pregnancies], this was due to spontaneous rotation, and in 25.2%, it was due to successful ECV," explained the study authors, all from the Fetal Medicine Research Institute at King's College Hospital, London.

By birth, 43.8% of fetuses initially presenting as noncephalic had a cephalic presentation. 

The study identified several reasons for not attempting ECV, including parental refusal, planned cesarean sections for non–presentation-related factors, spontaneous rotation prior to the planned ECV, and onset of labor or membrane rupture before the procedure.

Multivariable analysis demonstrated that maternal and pregnancy characteristics influenced the likelihood of noncephalic presentation at the 36-week scan, successful ECV, and spontaneous rotation. However, predictive performance was limited, with the area under the receiver operating characteristics curve ranging from 0.608 to 0.717. Detection rates (at a 10% false-positive rate) varied from 19.0% to 33.7%.

The authors concluded that routine ultrasound at 35+0 to 36+6 weeks could significantly reduce the risk of unexpected abnormal fetal presentations during labor. However, they emphasized the importance of an additional scan when women present in labor to ensure accurate fetal positioning.

These findings underscore the need for health-care providers to consider routine late-pregnancy ultrasounds—and, potentially, additional scans during labor presentation—to optimize maternal and fetal outcomes.

The study authors declared no conflicts of interest.