Date of Award

January 2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Nursing

First Advisor

Jody Ralph

Abstract

Background and Purpose: Overweight and obesity are common problems in the United States contributing to significant morbidity. Women may have increased risk for overweight and obesity over their lifetimes if they retain weight postpartum and never lose it. Increasingly, children are diagnosed as overweight or obese. Identification of overweight and obesity in young children coupled with the increased obesity rates in the adult population suggests that maternal factors may be associated with offspring obesity. Body mass index (BMI) and gestational weight gain are two factors that have been associated with increased weights postpartum in women, but these studies have mainly utilized participants who have had more than one baby in their lifetimes. There is little information on postpartum weight and offspring outcomes for women having their first baby. The purpose of this study was to investigate the importance of BMI and excessive gestational weight gain on postpartum weight retention and offspring weight out to 2 years in women having their first baby.

Study Design and Theoretical Framework: This is a retrospective secondary analysis of a prospective longitudinal study of women who were followed during their first pregnancy and up to two years postpartum. Postpartum weight retention and offspring weights were examined by maternal body mass index and ability to gain within the pregnancy guidelines set by the Institute of Medicine (IOM). The developmental model for origins of disease (Barker Hypothesis) is the theory used to frame this study. This theory hypothesizes that a critical event during gestation alters gene expression resulting in potential long-term consequences on human development. Specific Aims: 1) To determine if overweight or obese first time mothers retain

more weight gained in pregnancy than first time mothers of normal weight at 6 weeks, 6 months, 1 year and 2 years postpartum; 2) To determine if first time mothers who gain in excess of IOM guidelines during pregnancy retain more weight than women who gain within the IOM guidelines at 6 weeks, 6 months, 1 year and 2 years postpartum; 3) To determine if the offspring of overweight or obese first time mothers have higher weight for length percentiles than the offspring of first time mothers of normal weight mothers at 6 weeks, 6 months, 1 year and 2 years of life; and, 4) To determine if the offspring of first time mothers who gain in excess of IOM guidelines during pregnancy have higher weight for length percentiles than the offspring of first time mothers who gain within the guidelines at 6 weeks, 6 months, 1 year and 2 years postpartum.

Sample: Data from 652 mother/infant dyads were available for analysis. The women who provided the data were eligible for midwifery care in a low risk obstetrical setting. Underweight women at the initiation of pregnancy care were excluded from analysis.

Methods: A series of one-way analysis of variance (ANOVA) were used to compare normal, overweight and obese participants on demographic variables, postpartum weight retention (PPWR) and offspring weight for length percentiles. A 3x2 between subjects ANOVA was used to compare postpartum weight retention and offspring weight for length percentiles by adherence to weight gain guidelines. Follow-up non-parametric tests were then run because the Shapiro-Wilk test for normality of data was significant and the Levene’s test of homogeneity of variances was significant (p <.01). Kruskal-Wallis and Mann Whitney tests to determine significant differences between groups were completed.

Results: In the analysis of the demographic data, three observations were made: 1) normal weight women had significantly more years of education than obese women (p = .01), 2) obese women gained significantly less weight during pregnancy than normal weight women (p < .05), and 3) offspring of obese women were statistically significantly heavier at birth compared to normal weight women (p < .01), but the amount by which they were heavier is unlikely to be clinically significant.

Specific Aim 1: Obese women retained significantly less weight than normal and overweight women at 6 weeks (p < .05). Normal weight women retained significantly less weight than overweight women at the 6-month time point (p < .05). Normal weight women retained significantly less weight than overweight women at the 1year time point (<.05).

Specific Aim 2: In an analysis between groups, significant differences for weight gain in excess of the IOM guidelines were seen at the 6-week time period only (p < .01). Subsequent Mann-Whitney tests for weight gain in excess of IOM guidelines revealed that normal weight women who gained in excess of their guideline retained significantly more weight than obese women who gained outside of their guideline (p<.01) and overweight women who retained in excess of their guideline retained significantly more than obese women who gained in excess of their guideline. No other pairwise comparisons were significant.

In an analysis within groups, normal weight women who gained within their IOM guideline retained significantly less weight than normal weight women who gained in excess of the IOM guidelines at 6 weeks, 6 months, and 1 year time point (p < .01). No difference was seen for normal weight women who gained within their guidelines and those who did not at 2 years. Overweight women who gained within the IOM guidelines retained significantly less weight than overweight women who gained in excess of the IOM guideline at 6 weeks, 6 months and 1 year (p < .01). No difference was seen for overweight women who gained within their guideline and those who did not at 2 years. Obese women who gained within their IOM guideline retained significantly less weight at 6 weeks only (p <.05). No significant differences were seen for postpartum weight retention for obese women who gained within their guidelines and those who gained in excess of their guideline at any other time point.

Specific Aim 3: No significant differences were detected for offspring weight for length percentiles at any time point for any maternal BMI category.

Specific Aim 4: Offspring of normal weight women who gained within the IOM guidelines had significantly lower weight for length percentiles at the 1-year time point only (p=.05). For all other women in all BMI groups there were no differences at any time point.

Conclusions: Obese women had better outcomes than expected with less overall weight gain and less weight retention at 6 weeks. In general, while women who gained in excess of the guidelines tended to retain more weight, this was only seen at the 6-week time period for obese women and compared to normal and overweight women obese women who gained in excess of guidelines retained less weight postpartum. In this study of first time mothers with relatively uncomplicated pregnancies the offspring outcomes were not influenced by maternal BMI. Offspring of normal weight women who gained within their IOM guideline had significantly lighter babies at 1 year compared to normal weight women who over-gained.

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