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