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).

Previous studies of twin growth in the womb involved 2D ultrasound scans and had documented decreased twin growth relative to singletons only in the early 3rd trimester (28 to 40 weeks). Scientists do ...

Twins have proportionally less fat tissue accumulation in utero compared with singletons as early as 15 weeks of gestation, ...

Conjoined twins occur when identical twins have fused bodies ... Conjoined twins are typically diagnosed early on in pregnancy with ultrasound. The prognosis for conjoined twins is not good.

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).