Study questionDo all zygotes with three observed pronuclei have an actual triploid chromosomal complement?Summary answerNot all zygotes with 3 pronuclei observed are triploid, most of embryos with two even pronuclei and one smaller micronucleus are diploid.What is known alreadyIn the in vitro fertilization (IVF) setting, normal oocyte fertilisation is commonly confirmed 16–19 hours after conventional insemination or intracytoplasmic sperm injection (ICSI) with the appearance of two pronuclei (2PN).The presence three pronuclei (3PN) shows an abnormal oocyte fertilization. The incidence of 3PN zygotes in IVF is between 5.0%- 8.1% in conventional insemination and between 2.0%- 6.2% in ICSI. 3PN fertilized embryos are commonly discarded due to the suspected increased risk of a triploid chromosomal complement.However, no …