[Order of twins--random choice of natural selection?].

OBJECTIVE

Testing of hypothesis that the order of twins is random.

DESIGN

Confrontation of birthweight and incidence of stillbirth between twins.

MATERIALS AND

METHODS

The group of 829 twin deliveries was investigated. Probability of distribution was assessed according to Bernoullie's trials schema.

RESULTS

The first twin was usually heavier then the second one (p = 0.05), especially at term. Order of twin delivery was influenced by a birthweight difference > 250 g. In cases of single twin intrauterine death, the alive, term baby was delivered as the first one statistically more common (p = 0.029), despite of smaller number of cases. Discussion suggests that differences between twins are rather reasons of observed order than results.

CONCLUSION

Hypothesis of natural selection of stronger baby for the first delivery was presented.