The effects of maternal height on birth outcomes

A large body of literature has assessed the association between pre-pregnancy body mass index (BMI) and adverse birth outcomes, however, the effects of maternal height, irrespective of BMI, have been understudied. In this thesis I evaluated the association between maternal stature and adverse perinatal outcomes, and whether this association is modified by maternal race/ethnicity. I also examined how maternal stature modifies the association between small- and large-for-gestational age infants (SGA and LGA, respectively) and adverse neonatal outcomes. I conducted two retrospective cohort studies using data on all singleton births in the USA in 2016 and 2017, obtained from the National Center for Health Statistics (NCHS). Short and tall stature were defined as 90th centile of the maternal height distribution, respectively; maternal race/ethnicity included non-Hispanic White, non-Hispanic Black, American Indian/Alaskan Native, Asian/Pacific Islander, and Hispanic categories. SGA and LGA infant categories were defined using the United States’ reference for fetal growth. Adverse outcomes included, for example, preterm birth, perinatal death, and neonatal morbidity. Regression models were used to adjust for potential confounding and to assess effect modification. Overall, short women had an increased risk while tall women had a decreased risk of adverse perinatal outcomes relative to average stature women. Associations between maternal height and adverse perinatal outcomes were modified by race/ethnicity: the magnitude of the associations between maternal height and adverse perinatal outcomes were larger among some racial/ethnic groups and attenuated in others. When investigating risks of adverse neonatal outcomes among SGA and LGA infants, I found that the association between SGA and adverse neonatal outcomes was weaker in women of short stature, while it was stronger in women of tall stature. These findings raise important questions about the existing SGA/LGA classification since the medical prognosis for these infants also depends on maternal height. The findings of my thesis including various adverse perinatal health outcomes associated with maternal stature, race/ethnicity, and size for gestational age fill gaps in the literature regarding the modifying effects of maternal stature. The results provide health care providers with additional information that can improve risk assessment in pregnant women.Medicine, Faculty ofObstetrics and Gynaecology, Department ofGraduat