Median length of hospital stay for mother and baby after birth
Whether mother took supplements prior to becoming pregnant or during pregnancy
Babies admitted to neonatal intensive care unit or special care nursery after they were born
Babies who do not seem to notice their twin
If parent dresses twins in matching outfits
Babies aged 9-months old who passed or failed the target score expected of 10-month-olds for individual developmental areas measured by Ages and Stages Questionnaire
Whether the twin is identical or fraternal