In the Netherlands, between 2005 and 2011 the twin birth rate decreased from 18.6 to 15.9 per 1000 deliveries. The rise in the number of twin births in the 1980s and 1990 s is not only the consequence of a increase in the number dizygotic twins, but also of a small increase in the number of monozygotic twins. On IVF treatment single embryo transfer is increasingly taking place. This has led to a reduction of dizygotic twins but this does not prevent the development of monozygotic twins. In total, the number of twin pregnancies after IVF treatment has decreased from 803 in 2003 (21.7% of all pregnancies following IVF treatment) to 381 (8.5%) in 2011. Despite the big decline in the perinatal mortality rate over recent years, the risk of still birth or infant death clearly remains much higher in pregnancies with multiples than with singletons. The average gestational age of both monozygotic and dizygotic twins has decreased.