The Presence of Maternal Hypertension as an Effect Modifier in the Relationship Between Intrapair Birth Weight Discordance and Infant Mortality in Live Twin Births Open Access

Carssow, Katherine Lee (2011)

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Objective: To determine whether the presence of maternal hypertension interacts with intrapair twin
birth weight discordance to affect the association between birth weight discordance and infant
mortality among live twin births.
Study Design and Methods: The study used the matched multiple birth data set compiled by the
National Center for Health Statistics (NCHS), which contains matched records for all multiple births in
the United States from national birth and death certificate data from 1995-2000. Birth weight
discordance was expressed as a percentage based on the weight of the larger twin, and classified into 5
categories: <15%, 15-19%, 20-24%, 25-29%, and ≥30%. Infant mortality was defined as any set of twins
in which one or more members did not survive the first year of life. Crude prevalence and odds ratios of
infant mortality were calculated for each level of birth weight discordance, presence of maternal
hypertension, and selected covariates.
Results: The analysis used a total sample size of 289,953 live twin sets. The crude rates of infant
mortality in the highest and lowest categories of birth weight discordance were 9.4% and 2.5%,
respectively. The unadjusted association between weight discordance and infant mortality was
significant both with and without considering the interaction between weight discordance and maternal
hypertension. The association between maternal hypertension and birth weight discordance was also
significant (OR 1.62, 95% CI 1.54-1.70).When the model associating death with birth weight discordance
was adjusted for maternal demographics along with parity, placental abruption, gestational age, and
presence of a congenital anomaly, the effect was attenuated. The p-value for the interaction term in the
final model was p=0.70.
Conclusion: Interaction between birth weight discordance and maternal hypertension does not appear
to effect the association between weight discordance and infant mortality when important covariates
are considered.

Table of Contents

Chapter 1

Background and Literature Review...4
Chapter 2



Chapter 3

Public Health Implications...19

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