LOWER MORTALITY FOR FEMALE-FEMALE TWINS THAN MALE-MALE AND MALE-FEMALE TWINS IN RURAL SENEGAL

Twins have been registered prospectively for 12-22 years in 42 small v illages in the Bandafassi area of Eastern Senegal. We studied 98 pairs of twins to test whether twins in opposite sex pairs have higher post neonatal mortality than same sex twins. Neonatal mortality for twins w as 41.3%; mortality for infants and for children under age 5 years was 53.0% and 66.8%, respectively. Neonatal mortality was identical for s ame-sex and opposite-sex twin pairs, but much higher for boys than gir ls [relative risk = 1.8; 95% confidence interval (CI) = 1.2-2.6]. Ther e was clustering of double neonatal deaths for all types of twins. In the postneonatal period, female-female twins had lower mortality than other twin types. Twins had higher postneonatal mortality as long as t he co-twin was alive [mortality rate ratio (MR) = 2.6; 95% CI = 1.0-6. 7]. Girls had excess mortality when the co-twin was of the opposite se x (MR = 4.3; 95% CI = 1.2-15.3), whereas there was no difference for b oys. In conclusion, contact with a co twin of the opposite sex increas ed child mortality for female twins. Our data are not sufficient to de termine whether this difference is specific for girls or applies to bo ys as well.