Vernix caseosa, a greasy white substance made of lanugo, oil and dead skin cells (yum) now coats baby's skin, shielding it from the amniotic fluid. (Picture yourself after a nine-month bath, and the need for protection makes sense.) You might actually get to see the vernix at birth, especially if baby is premature.
Since the twins are probably going to arrive a month early I'll probably see the vernix.
I know I reported on week 18 two days ago, but this is my attempt to catch up on fruits since I actually started week 20 yesterday. In the past week though I happened to eat two whole mangos (they're a good source of Vitamin A and C).