Outcomes in Twin Pairs: Is the Smaller Twin at Greater Risk?

Abstract 1512

Twin pregnancies are often complicated by discordant intrauterine growth. It remains unclear whether the smaller twin is at increased risk for poor outcome, and if there is a relationship between discordancy and outcome. The purpose of this study was to evaluate the outcome of twins based on size and discordancy. Methods: We evaluated 82 pairs of twins born between 7/93 and 7/98 cared for in a single Level III NICU (n=164). Twins were included if at least 1 infant had a birth weight < 1500g and both were live-born. Discordance was calculated by the following formula: (birth wt of larger twin minus birth wt of smaller twin)/birth wt of larger twin. Statistical methodology included Student's t-test, Chi-Square analysis, and logistic regression. Data are expressed as mean ± standard deviation or odds ratio (OR) with 95% confidence interval (CI). A p value< 0.05 was considered to be significant. Results: The gestational age of the cohort was 29.5 ± 2.7 wks, 60% were male, 74% white and 26% non-white. Birth weight was 1023 ± 282 g among smaller twins and 1315 ± 429g among larger twins (p<0.01). The twins were 19.2 ± 17.6% discordant (range 0-75, median 13%). Twins with IVH were not more discordant (12.5%) than those without IVH (18.5%, p=0.11). There was also no statistical difference in discordance in twins with grade III-IV IVH (7%) vs those without IVH (18%, p=0.07). Similarly, surviving twins were not more discordant (19%) than those who died (20%, p=0.84). There was no increase in discordance in the twins with PVL, BPD, PDA, or NEC. Those twins who were > 15% discordant (n=68) were not more likely to have IVH (11% vs 23%, p=0.07), grade III-IV IVH (2% vs 10%, p=0.11), or mortality (11% vs 13%, p=0.22) than twins who were <15% discordant. However, twins with >15% discordance were of greater gest. age (30.7 ± 2.7 vs 28.5 ± 2.3, p<0.01) than those <15% discordant. After controlling for gest. age, discordancy >15% was not associated with an increased odds of IVH (OR 0.54, 95% CI 0.2-1.6, p=0.27), grade III-IV IVH (OR .28, 95% CI 0.3-2.5, p=0.3), or mortality (OR 1.8, 95% CI 0.6-5.5, p=0.3). We also analyzed the individual twin within each pair as smaller or largely by weight. The smaller of each twin pair was not at increased risk of IVH (18 vs 22%, p=0.59), grade III-IV IVH (7 vs 7%, p=0.94), or mortality (14 vs 11%, p=0.83) than their larger counterparts. Smaller twins had a longer length of hospitalization (57.5 ± 26.2 vs 48.1 ± 23.9 days, p=0.03) and greater weight gain per day (15.3 ± 4.7 vs 11.8 ± 8.0 g/day, p<0.01) than larger twins. Conclusions: In our population, smaller twins were not at increased risk for IVH or mortality, and had a greater rate of weight gain than larger twins. Discordancy was not associated with an increase in mortality. The trend towards a decreased incidence of IVH in twins who were more discordant needs further investigation with a larger number of infants.

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Touch, S., Leef, K., Pearlman, S. et al. Outcomes in Twin Pairs: Is the Smaller Twin at Greater Risk?. Pediatr Res 45, 257 (1999). https://doi.org/10.1203/00006450-199904020-01529

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