Annuality of birth, delivery types and sex ratio in Tehran, Iran.

616,638 births during 1967-1983 from a maternity hospital in Tehran (Iran) have been considered for the present study. The mean rate of normal delivery was 92.59%, that of Caesarean was 3.09%, that of wantose was 1.52% and finally that of forceps was 1.31%. Caesarean and wantose (vacuum extractor) delivery types showed an increasing trend, whereas the normal and forceps delivery types showed a decreased trend during the period under study. The secondary sex ratio was the highest in 1977 and the lowest in 1983 with a mean of 105.18. The twinning rate showed a decreasing trend during the above period.