Maria Sevoyan

Date of Award

Fall 2020

Document Type

Open Access Dissertation


Epidemiology and Biostatistics

First Advisor

Nansi S. Boghossian

Second Advisor

Marco Geraci


Optimal pregnancy outcomes and subsequent postnatal development in childhood are important contributors for health in adulthood. Some contributors to pregnancy outcomes include interpregnancy interval (IPI) and gestational age. Postnatal growth patterns also contribute to neurodevelopment and metabolic health outcomes later in life.

Several systematic reviews consistently show that short and long IPIs are associated with increased risk of subsequent adverse perinatal outcomes. Recent studies demonstrate that previously observed consistent positive associations between short and long IPIs and adverse perinatal outcomes might be due to unmeasured confounding rather than the length of the IPI. We used the National Institute of Child Health and Human Development (NICHD) Consecutive pregnancies dataset. Utilizing within-woman comparison design, we did not find evidence that short IPI categories (months) compared to the recommended IPI of 18-23 months were associated with higher odds of any of the examined perinatal outcomes including preterm birth, low birth weight, small-for-gestational-age (SGA), and neonatal intensive care unit admission. Intervening on short IPI may not be beneficial for decreasing the rates of adverse perinatal outcomes. Longer IPIs (≥24 months) compared to the reference IPI were associated with increased odds of delivering a low birth weight infant in the subsequent pregnancy.

Prior preterm birth (PTB) is the strongest predictor of subsequent PTB; however, there is limited research examining whether prior early term birth (37-38 weeks of gestation, ETB) is associated with increased risk of subsequent PTB and ETB. Thus, we examined how early term birth (ETB) in the first pregnancy affects the gestational duration of the second pregnancy. For study two we used the same NICHD Consecutive pregnancies study dataset. We found that compared to the women with prior birth at ≥39 weeks of gestation, women with prior ETB were at higher risk for a subsequent PTB and ETB. Increased risks of PTB and ETB were also present in all combinations of subtypes i.e. spontaneous, indicated, and elective. The higher risks varied by birth subtypes. Prior early term deliveries signal a higher risk of delivering preterm and early term infant in the subsequent pregnancy. This knowledge may help to identify women at high risk and can be used for counseling women for subsequent pregnancies, especially women with prior spontaneous ETB.

Postnatal rapid weight gain in SGA infants is associated with increased risk of obesity and other metabolic outcomes later in life but appears to be beneficial for neurocognitive function. Defining optimal growth for SGA infants is challenging. Thus, we aimed to identify weight growth trajectories from birth to 7 years of age among term SGA infants and to examine the association between the identified weight growth trajectories and health outcomes at 7 years of age. We used the UK Millennium Cohort Study (MCS) data from birth to 7 years of age (MCS1 to MCS4 sweeps). We identified six distinct weight growth trajectories during the period from birth till 7 years of age using Group-Based Trajectory Modeling. These trajectories were labelled as “minimal weight gain” (trajectory A, n=83, 6.8%), “slow weight gain” (trajectory B, n=425, 34.8%), “moderate weight gain” (trajectory C, n=406, 33.3%), “fast gain after drop before 9 months” (trajectory D, n=69, 5.7%), “more than moderate gain” (trajectory E, n=198, 16.2%), and “excessive weight gain” (trajectory F, n=39, 3.2%). As compared to appropriate-for-gestational-age infants, infants with minimal (trajectory A) and slow (trajectory B) weight gain had increased odds of growth restriction and suboptimal cognition scores at 7 years of age. On the other hand, children who followed excessive (trajectory F) and more than moderate weight gain (trajectory E) trajectories had higher odds of being overweight or obese at 7 years of age. SGA infants in trajectory D (characterized as fast gain after the drop before 9 months) had increased odds of receiving suboptimal scores on all cognitive tests. Infants in the moderate gain trajectory (trajectory C) had lower odds of overweight and obesity, however, did not demonstrate evidence of increased odds of suboptimal scores on all cognitive tests. The study results suggest that in term SGA infants a moderate gain trajectory (Trajectory C) that is characterized with rapid weight gain reaching the median weight around 3 years of age and then maintaining weight around the median from 3 to 7 years of age may be associated with a lower risk of childhood health outcomes at 7 years of age. The study suggests that weight growth patterns may be important contributors for future childhood health, but the associations between different growth patterns and childhood outcomes observed in this study may be not causal. Improving growth (or following a specific growth trajectory) might not improve the childhood outcomes. Suboptimal childhood outcomes may be an indicator of a poor environment.

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