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Differences in twins the importance of birth order

American Journal of Obstetrics & Gynecology 151(7): 915-921
Differences in twins the importance of birth order
Despite the clinical impression that 1st-born twins do better than 2nd-born twins, recent reports have shown no difference in perinatal mortality between them. To evaluate differences in twins, more sensitive means than perinatal deaths are necessary. This study examines differences between 80 1st-born and 2nd-born twin pairs with respect to Apgar score, umbilical venous and arterial blood gas, and acid-base data. The umbilical venous and arterial blood PO2 [partial pressure of O2], PCO2 [partial pressure of CO2], base deficit, pH and lactic acid concentration were measured in paired samples and compared with the paired t test and .chi.2 when applicable. Statistically significant differences favoring twin A, the 1st-born, were found in 1 min Apgar score, umbilical venous pH, PO2 and PCO2, and umbilical arterial PO2. The factors in umbilical venous and arterial blood did not show statistically significant differences. When these parameters were examined with respect to route of delivery, monochorionic and dichorionic twins, interval between twins and vertex twins only, with the possible effects of malpresentation eliminated, the results persistently favored the 1st-born twin. It is unequivocally demonstrated that there are substantial differences at birth favoring the 1st twin, despite similar perinatal mortality for both. Apparently, the 2nd-born twin has potentially greater susceptibility to hypoxia and trauma.

Accession: 005151707

PMID: 3920911

DOI: 10.1016/0002-9378(85)90670-2

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