ABSTRACT
The classification of multiple pregnancy is based on:
Non-identical/fraternal/dizygotic/binovular twins result from the fertilization of two separate ova, spontaneously released at ovulation, by two spermatazoa. Although they always have two functionally separate placentae (dichorionic), the placentae can become anatomically fused and appear to the naked eye as a
In the UK, twins currently account for approximately 1.5 per cent of all pregnancies. Higher multiples occur in approximately 1 in 2500 pregnancies. The causes of monozygotic twinning are unknown, but dizygotic twinning and higher multiples are associated with increasing maternal age, high parity, black race and increased maternal height and weight. Black races have the highest prevalence of twins, Japanese have the lowest.
