caa a22 4500 388058765 CHVBK 20180307125114.0 cr unu---uuuuu 161130e19980401xx s 000 0 eng 10.1375/twin.1.2.57 doi S1369052300000234 pii (NATIONALLICENCE)cambridge-10.1375/twin.1.2.57 Trends in the twinning rate in Johannesburg, South Africa, 1969-1989 and estimated twinning rates for 1990 [Elektronische Daten] Birth statistics for the Johannesburg Metropolitan Region were collected for 757 151 confinements from 1969 to 1989 (467 513 Black, 194 375 White, 67 250 Coloured and 28 013 Indian confinements). From 1969 to 1978 data on the sexes of twins were also collected for 375 203 of the confinements (203 504 Black, 129 631 White, 28 253 Coloured and 13 815 Indian confinements). A twin confinement was defined as two deliveries during one confinement. Twinning rates (TRs), defined as the number of twin confinements per 1000 total confinements, were calculated per year for each population group and from 1969-1978 estimates of the relative proportions of dizygotic (DZ) and monozygotic (MZ) twins were calculated and thus the relative DZTRs and MZTRs. A significant decline in Black and Coloured TRs was observed between 1969 and 1989. A significant decline in Black DZTR but not Black MZTR was observed between 1969 and 1978, the Coloured twin sample was too small to show significant trends over this period. It is probable that the overall decline in Black twinning may be explained by a decline in the DZTR. An analysis of birth statistics for 159 748 confinements (134 504 Black and 25 244 White confinements) collected as part of a prospective study of TRs in the Johannesburg Metropolitan Region from 1988 to 1990, indicated that the Black TR continued to decline at least until the end of 1990. TRs in the Johannesburg Metropolitan Region calculated from City Health Department birth statistics collected from 1988 to 1990 were: 13.8 and 10.77 for the Black and White populations, respectively. TRs for this period calculated from the combined birth statistics of 14 hospitals, nursing homes and maternity clinics across the region were: 12.4 and 10.88 for the Black and White populations, respectively. Copyright © Cambridge University Press 1998 twins nationallicence twinning rate nationallicence trends nationallicence South Africa nationallicence africans nationallicence Hain Frances M. Department of Human Genetics, School of Pathology, South African Institute for Medical Research and University of the Witwatersrand, Johannesburg, South Africa. Kromberg Jennifer GR Department of Human Genetics, School of Pathology, South African Institute for Medical Research and University of the Witwatersrand, Johannesburg, South Africa. Twin Research Cambridge University Press 1/2(1998-04-01), 57-64 1369-0523 1:2<57 1998 1 THG https://doi.org/10.1375/twin.1.2.57 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1375/twin.1.2.57 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Hain Frances M. Department of Human Genetics, School of Pathology, South African Institute for Medical Research and University of the Witwatersrand, Johannesburg, South Africa NATIONALLICENCE 700 1- Kromberg Jennifer GR Department of Human Genetics, School of Pathology, South African Institute for Medical Research and University of the Witwatersrand, Johannesburg, South Africa NATIONALLICENCE 773 0- Twin Research Cambridge University Press 1/2(1998-04-01), 57-64 1369-0523 1:2<57 1998 1 THG CC0 http://creativecommons.org/publicdomain/zero/1.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-cambridge