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Differences in twins: the importance of birth order
American Journal of Obstetrics and Gynecology
|April 1, 1985
Summary
Firstborn twins show better birth outcomes than second-born twins, despite similar survival rates. This study highlights significant differences in Apgar scores and blood gas levels, indicating greater susceptibility to hypoxia for the second twin.
Area of Science:
- Neonatal Research
- Perinatal Medicine
- Twin Studies
Background:
- Clinical observations suggest firstborn twins fare better than second-born twins.
- Previous studies found no significant difference in perinatal mortality between firstborn and second-born twins.
- More sensitive indicators than perinatal death are needed to assess twin birth differences.
Purpose of the Study:
- To investigate birth outcome differences between firstborn (Twin A) and second-born (Twin B) twins.
- To compare Apgar scores and umbilical cord blood gas/acid-base data between paired twins.
- To identify potential vulnerabilities in second-born twins.
Main Methods:
- Study included 80 pairs of firstborn and second-born twins.
- Measured umbilical venous and arterial blood PO2, PCO2, base deficit, pH, and lactic acid.
- Utilized paired t tests and chi-squared tests for statistical analysis.
Main Results:
- Firstborn twins demonstrated significantly higher 1-minute Apgar scores.
- Umbilical venous pH, PO2, and PCO2 were significantly higher in firstborn twins.
- Umbilical arterial PO2 was also significantly higher in firstborn twins.
- These advantages for the firstborn twin persisted across different delivery methods and twin types.
Conclusions:
- Substantial birth differences favor the firstborn twin, despite similar perinatal mortality rates.
- Second-born twins may have a higher susceptibility to hypoxia and birth trauma.
- Neonatal assessment should consider the birth order of twins for accurate evaluation.