Date Published: January 30, 2019
Publisher: Public Library of Science
Author(s): Yanni Xiao, Minxue Shen, Shujuan Ma, Shi Wu Wen, Hongzhuan Tan, Yun-Wen Zheng.
Twins with discordant growth have increased risks of perinatal mortality and morbidity. Previous studies have identified a number of risk factors for inter-twin birth weight discordance, yet no study has examined the effect of maternal hepatitis C infection.
We used the twin birth records extracted from the 2011 to 2015 United States birth records created by the Centers for Disease Control and Prevention. The outcome variable of this study was inter-twin birth weight discordance, defined as [(birth weight of larger twin–birth weight of smaller twin) / birth weight of larger twin]. The independent association of hepatitis C infection with birth weight discordance was examined using the gamma regression or log binomial regression, adjusted by potential confounders.
Of the 270,256 twin pairs included in the final analysis, 850 (0.31%) had positive hepatitis C. Compared to mothers without hepatitis C, mothers with hepatitis C positive tended to have higher risk of birth weight discordance, but with no statistical significance. After adjustment for potential confounding factors, hepatitis C positive became a significant risk factor for birth weight discordance >25% (relative risk 1.14, 95% confidence interval 1.02−1.29). Sensitivity analyses (by treating birth weight discordance as a continuous outcome or dichotomizing into by different cutoffs) yielded similar results, with relative risks ranging from 1.07 to 1.12 (all P<0.05). Maternal hepatitis C positive is associated with inter-twin birth weight discordance, an important adverse infant outcome in twin pregnancies, although the effect size is small.
Approximately 16% of twin pregnancies have birth weight discordance of at least 20% . Compared with twins with birth weight concordance, twins with discordant growth have increased risks of perinatal mortality and morbidity . Identification of risk factors of inter-twin birth weight discordance is helpful in obstetric care of these pregnancies.
There were 664,490 twin records from 2011 to 2015 in the original files. Of these, 599,141 (90.2%) were successfully matched. After excluding records with missing information on outcome and critical co-variables, 540,512 twin records (or 270,256 pairs of twins) were included in the final analysis (Fig 1). The mean age of the included (HCV reported) and excluded women (HCV not reported, 9.3%) were 30.2 ± 6.0 and 30.4 ± 6.1 years, respectively; and the mean BMI of the two groups were 27.1 ± 6.9 and 27.5± 7.4 kg/m2, respectively. No major selection bias existed; as a result, imputation for missing data was not applied.
Our study based on a large cohort of twins in the United States demonstrated that twins born to mothers with HCV infection had significantly higher risk of developing inter-twin birth weight discordance than twins born to mothers without HCV infection, after adjusting for a number of known risk factors of birth weight discordance. This association remained essentially the same using different cut-off points or treating birth weight discordance as a continuous outcome variable. To our knowledge, this is the first study that has examined the association between maternal HCV infection and inter-twin birth weight discordance. The large sample of our study allowed a stable estimation and adjustment for a number of risk factors simultaneously. The association between maternal HCV infection and inter-twin birth weight discordance became stronger and statistically significant after adjusting for a number of confounding factors, including maternal demographic factors. We acknowledged that the effect size of HCV infection on birthweight discordance was not very large for clinical importance. However, it is still a problem, from scientific point of view, that may still worth exploration.