Dichorionic-Diamniotic (Identical or Fraternal) Twins 

In addition to pregnancies formed by the fertilization of two separate eggs by two separate sperms, the placenta is separate in monozygotic twins formed by the zygote formed by the fertilization of a single egg with sperm, splitting into two within the period until the 3rd day. 

In dichorionic-diamniotic twin pregnancies in which the placenta is separated, the problems have increased compared to singleton pregnancies and approximately 2% miscarriages, 2% fetal losses in the womb, 20% growth-weight retardation, 5% severe preterm births, and 1% organ defects-anomalies.