The National Institutes of Health April 7 released a study that found twins — smaller at birth on average than singletons — ...

A first-trimester ultrasound will confirm you're having di-di twins by showing ... happens early, about one to four days after fertilization. One-third of identical twins are di-di twins.

NIH findings could lead to more efficient monitoring of twin pregnancies.

Twins—smaller at birth, on average, than singletons—start out smaller in pregnancy than was previously known, according to a study by researchers at the National Institutes of Health (NIH).

Twins—smaller at birth, on average, than singletons—start out smaller in pregnancy than was previously known, according to a study by researchers at the National Institutes of Health (NIH).