a1 Department of Biological Psychology, VU University Amsterdam,
The Netherlands a2 Department of Child and Adolescent
Psychiatry, Academic Medical Center, Amsterdam, the Netherlands
a3 Department of Child and Adolescent Psychiatry, GGZ inGeest/VU
Medical Center, Amsterdam, the Netherlands a4 Department of
Obstetrics, Leiden University Medical Center, the Netherlands a5
PALGA Foundation, Utrecht, The Netherlands Birth weight in
triplets is, on average, lower than in singletons and twins, and
more children are classified as having very low or extremely low
birth weight. Still, there is limited research on factors that
affect triplet birth weight, and samples under study are often
small. Chorionicity and zygosity influence triplet birth weight,
but it is unknown whether the effect of zygosity can be entirely
ascribed to the effect of chorionicity or whether zygosity has
an additional effect on triplet birth weight. This question was
investigated in 346 triplets (from 116 trios) registered with
the Netherlands T