A term of 37 to 41 weeks is considered ''normal,'' but the new research finds birth at 39 to 41 weeks provides more developmental advantages compared to birth at 37 to 38 weeks.
"If the pregnancy is going well, it would be better to avoid doing elective C-sections early in the full-term window," said study author Dr. Betsy Lozoff, a professor of pediatrics and communicable diseases at the University of Michigan.
She and her colleagues tested 1,562 infants when they were 1 year old, then looked back to see at what week of term they were delivered. The  were all born in Chile and all were delivered within the full-term window. Their average birth weight was 6.6 pounds.
For every additional week in the womb, however, the mental developmental test scored increased very slightly, by 0.8. The psychomotor scores -- which relate to body movement and coordination -- increased by 1.4 points for every additional week. This held after the researchers accounted for birth weight, gender, socioeconomic status and home environment.
Very interesting! Are you opting for an induction or c-section? If so, at what week of pregnancy is baby set to arrive?