Azubuike J C
Br J Obstet Gynaecol. 1982 Jan;89(1):77-9. doi: 10.1111/j.1471-0528.1982.tb04641.x.
In a prospective study of multiple births conducted at three hospitals, a University Teaching Hospital, an urban Maternity Hospital and a Community Hospital, in Eastern Nigeria, the average incidence was found to be 35 per 1000 births. The twinning rate was found to increase progressively with both birth rank and maternal age, with an indication that parity plays the more important role.