Objective
The purpose of this study was to examine the relationship between maternal obesity that is calculated 9 months after delivery and sociodemographic variables.
Study Design
A national cohort of mothers was sampled 9 months after delivery as part of the Growing Up in Ireland Study Infant Cohort. Sociodemographic and clinical details were recorded at the interview by trained fieldworkers who used validated questionnaires. Body mass index was calculated based on weight and height measurements at the postpartum interview. The unadjusted and adjusted odds of obesity were calculated for predictor variables with the use of logistic regression analysis.
Results
Of the 10,524 mothers whose cases were studied, the mean age was 31.6 ± 5.5 years, and the mean parity was 1.0 ± 1.1. The mean body mass index after delivery was 25.7 ± 5.4 kg/m 2 ; 16.8% of the women (n = 1768) were obese. Postpartum maternal obesity levels were associated positively on univariable analyses with smoking, lower household income, African nationality, earlier completion of full-time education, gestational weight gain, lower breast-feeding duration, and increasing parity. On multivariable analysis, maternal obesity was associated with increasing parity in lower income households, but not in higher income households.
Conclusion
Public health interventions that are aimed at decreasing obesity levels after childbirth should prioritize women who are disadvantaged socioeconomically.
Maternal obesity has emerged as one of the most important challenges in modern obstetrics. It is common, clinically important, and costly. In wealthy countries, approximately 1 in 3 women of childbearing age are obese, based on a body mass index (BMI) of >29.9 kg/m 2 . In Europe, approximately 1 in 6 women who are seen for antenatal care is obese, and approximately 1 in 50 is morbidly obese.
There is strong epidemiologic evidence that maternal obesity is associated with an increase in both fetal and maternal complications. Thus, it is not surprising that maternal obesity is also associated with an increase in obstetric interventions, for example cesarean delivery, and an increase in healthcare use. In general, increases in obesity-related diseases are projected to add $48-66 billion a year to healthcare costs in the United States and £1.9-2 billion a year in the United Kingdom by 2030. Moreover, maternal obesity potentially has lifelong consequences for the health of the woman and her offspring. The human and financial costs, the intergenerational impact, the increased prevalence, and the potential modification as an obstetric risk factor have all focused attention on the public health issue of obesity and pregnancy.
The level of concern is so high that, after a comprehensive systematic evidence-based review of the literature, the Institute of Medicine (IOM) produced a detailed report that has revised downwards the recommendations for gestational weight gain (GWG) in obese women. Their decision was based primarily on maternal considerations rather than fetal considerations. In particular, there was concern about the association between increased GWG and postpartum weight retention and obesity complications later in a woman’s life. The literature review separated studies on postpartum maternal weight changes into short-term (<11 weeks), intermediate (3 months to 3 years), and long-term (>3 years). However, it acknowledged that there is a dearth of information about postpartum maternal weight changes. The information that does exist often lacks quality.
The objective of this national observational study was to examine the relationship between maternal obesity 9 months after delivery and sociodemographic variables.
Materials and Methods
A nationally representative sample of 11,134 infants and their families was selected from the Child Benefit Register that is maintained by the Department of Social Protection for the Infant Cohort of Growing Up in Ireland study. In the Republic of Ireland, Child Benefit is provided for all children, irrespective of parental means. Children who were born between December 2007 and May 2008 were selected randomly into the sample for the Growing Up in Ireland study at 9 months of age; it is their mothers who were included in this study.
A total of 73,662 infants were recorded on the Child Benefit Register for the calendar year 2008. The mothers of 16,136 infants were invited to take part in the study. Of these, 11,134 women agreed to participate, which is a response rate of 69%. In line with best practice, the completed sample was grossed statistically (reweighted) on the basis of external population estimates taken from the census of the population.
Parents were first sent a letter that explained the aims of the infant cohort study and what would be involved, including a date for the fieldworker to visit the house. If agreeable, a trained fieldworker arrived at the address and carried out a computer-assisted personal interview with the parents, one of whom would be nominated as the “primary caregiver” by the parents (where both were resident). The parents were also asked to self-complete a supplementary questionnaire on a laptop that was provided. The supplementary questionnaire included questions of a more sensitive personal nature. Self-completion is a well-validated method of minimizing response bias. Interviews took place between September 2008 and April 2009.
Maternal weight was recorded at the interview 9 months after delivery with a medically-approved flat mechanical scale (seca 761; seca north american east, Hanover, MD) that graduated in 1-kg increments and had an upper capacity of 150 kg. Maternal height was measured with a Leicester portable height stick (seca north american east). Maternal BMI was calculated, and maternal obesity was defined as a BMI of >29.9 kg/m 2 .
Data were collected on maternal age, maternal citizenship (Irish, United Kingdom, European Union countries admitted to the Union before May 2003, European Union countries admitted after May 2003, African, Asian, other citizenship), highest level of education (lower secondary, upper secondary, post-secondary, third level), household income (net income, equivalized for household size and composition and grouped into quintiles with a missing category), and current level of cigarette smoking (none, occasional, light [<11 per day], medium [11-19 per day], heavy [≥20 per day]).The previous number of children who were born to the mother and still living either with her or in another location were recorded. Parity is presented as 4 categories (1, 2, 3, and ≥4) in unadjusted analyses and as a linear scale in adjusted analyses. Reported maternal weight gain in pregnancy is used in 3 categories (<10 kg, 10-15.9 kg, and ≥16 kg and a missing category). Reported breast-feeding is used in 5 categories (none, <1 month, <6 months, and ≥6 months and a missing category].
The unadjusted and adjusted odds of obesity were calculated for predictor variables with logistic regression analyses; all variables were entered simultaneously. Ethical approval for the Growing Up in Ireland Study was received from the Research Ethics Committee of the Department of Children and Youth Affairs of the Government of the Republic of Ireland.
Results
We omitted 564 cases because of missing height and/or weight information. We omitted a further 55 cases because of missing information on 1 of the variables in the analyses (10 cases) or because the primary caregiver who responded was male (38 cases) or not the natural mother of the child (7 cases), which left 10,524 cases for analyses.
The characteristics of the study population are shown in Table 1 . Table 2 gives descriptive statistics for the sample that include the proportion of obesity by characteristic and the unadjusted odds ratio. This shows that women with an African nationality were 2.68 times ( P < .001) more likely to be obese than women from Ireland, whereas women from those countries that joined the European Union before May 2003 or countries in Asia were less likely to be obese (odds ratio, 0.63 [ P = .001] and 0.34 [ P = .006], respectively). There was no increase in the odds of obesity with increasing age in unadjusted analyses, but there was an increase with parity. A third child increased the odds of obesity by 29% ( P = .004) relative to the first, and ≥4 children increased the odds by 63% ( P < .001).
| Characteristic | Mean | 95% confidence interval |
|---|---|---|
| Age, y | 31.6 | 31.5–31.7 |
| Parity, n | 1.0 | 0.97–1.01 |
| Body mass index, kg/m 2 | 25.7 | 25.5–25.8 |
| Weight gain last pregnancy kg | 13.4 | 13.3–13.5 |
| Obese: body mass index >29.9 kg/m 2 , % | 16.8 | 15.9–17.6 |
| Initiated breast-feeding with last child, % | 56.2 | 55.3–57.2 |
| Smoker, % | ||
| Occasional | 7.5 | 6.9–8.1 |
| Light | 11.0 | 10.2–11.7 |
| Medium | 6.4 | 5.8–7.0 |
| Heavy | 8.1 | 7.5–8.8 |
| Mean equivalized household income (euro) | 21,608 | 21,299–21,917 |
| Variable | Unweighted, n | Weighted, % | Obese, % | Unadjusted odds ratio | 95% CI |
|---|---|---|---|---|---|
| Nationality | |||||
| Irish | 8496 | 84.9 | 16.8 | 1 | |
| United Kingdom | 214 | 1.9 | 17.8 | 1.07 | 0.69–1.66 |
| EU12 a | 896 | 6.1 | 11.3 | 0.63 | 0.48–0.83 |
| EU14 b | 129 | 1.0 | 14.0 | 0.81 | 0.44–1.47 |
| African | 144 | 1.1 | 35.1 | 2.68 | 1.70–4.23 |
| Asian | 137 | 1.1 | 6.5 | 0.34 | 0.16–0.74 |
| Other | 508 | 4.1 | 22.8 | 1.46 | 1.12–1.91 |
| Maternal age, y | |||||
| <25 | 1206 | 12.0 | 15.9 | 1 | |
| 25-29 | 2239 | 21.0 | 18.4 | 1.19 | 0.95–1.50 |
| 30-34 | 3640 | 35.4 | 16.4 | 1.04 | 0.84–1.29 |
| 35-39 | 2771 | 25.4 | 15.7 | 0.98 | 0.79–1.23 |
| ≥40 | 668 | 6.2 | 19.5 | 1.28 | 0.95–1.72 |
| Parity, n | |||||
| 1 | 4242 | 40.6 | 15.2 | 1 | |
| 2 | 3399 | 33.1 | 16.2 | 1.07 | 0.93–1.25 |
| 3 | 1836 | 17.8 | 18.7 | 1.29 | 1.08–1.53 |
| ≥4 | 1047 | 8.5 | 22.6 | 1.63 | 1.33–1.99 |
| Pregnancy weight gain, kg | |||||
| <10 | 3031 | 30.0 | 15.7 | 1.06 | 0.91–1.25 |
| 10-15.9 | 3651 | 34.2 | 14.9 | 1.00 | |
| ≥16 | 2416 | 22.3 | 16.1 | 1.10 | 0.92–1.30 |
| Data missing | 1426 | 13.6 | 24.9 | 1.90 | 1.58–2.27 |
| Breast-feeding, mo | |||||
| None | 4159 | 43.8 | 19.8 | 1.00 | |
| <1 | 978 | 9.3 | 15.4 | 0.74 | 0.59–0.92 |
| <6 | 2163 | 19.2 | 13.7 | 0.64 | 0.54–0.77 |
| ≥6 | 1609 | 13.1 | 11.5 | 0.53 | 0.43–0.65 |
| Data missing | 1615 | 14.7 | 17.4 | 0.86 | 0.72–1.02 |
| Current smoking | |||||
| None | 7235 | 67.0 | 16.2 | 1 | |
| Occasional | 772 | 7.5 | 16.0 | 0.99 | 0.77–1.26 |
| Light | 1080 | 11.0 | 16.4 | 1.02 | 0.83–1.25 |
| Medium | 636 | 6.4 | 18.5 | 1.18 | 0.92–1.51 |
| Heavy | 801 | 8.1 | 21.6 | 1.43 | 1.15–1.77 |
| Highest level of education c | |||||
| Lower secondary | 1230 | 17.7 | 22.4 | 2.45 | 2.02–2.98 |
| Upper secondary | 2018 | 25.2 | 20.0 | 2.13 | 1.80–2.52 |
| After secondary | 3455 | 27.8 | 16.9 | 1.73 | 1.48–2.01 |
| Third Level | 3821 | 29.3 | 10.5 | 1 | |
| Household net equivalized income (quintile) | |||||
| Lowest | 2070 | 18.3 | 23.6 | 2.58 | 2.09–3.20 |
| Second | 1822 | 18.6 | 19.5 | 2.04 | 1.64–2.53 |
| Third | 1854 | 18.4 | 16.4 | 1.65 | 1.32–2.05 |
| Fourth | 2110 | 20.3 | 14.1 | 1.38 | 1.11–1.72 |
| Highest | 1880 | 17.3 | 10.7 | 1 | |
| Data missing | 788 | 7.2 | 15.4 | 1.53 | 1.14–2.05 |
a Those countries that joined the EU before May 2003
b Those countries that joined the EU after May 2003
c The equivalent of secondary education in Ireland is high school education in the US.
Heavy smoking (≥20 cigarettes daily) increased the odds of obesity by 43% ( P = .001); lower levels of smoking were not associated with an increase in the risk of obesity in unadjusted analyses. Education and household income level showed pronounced gradients with maternal risk of obesity in unadjusted analyses. Women with lower secondary educational qualifications were 2.45 times ( P < .001) more likely to be obese than women with third level qualifications. Women in the lowest income quintile were 2.58 times ( P < .001) more likely to be obese than women in the highest income quintile.
Self-reported GWG did not correlate with the risk of obesity after delivery, except for those women whose data on GWG were missing (1 in 6). Among this group, the risk of obesity increased by 90%. There was a dose-response relationship between breast-feeding the last child and obesity in unadjusted analyses. Breast-feeding for ≥6 months reduced the odds of obesity by 47%. Refusal to provide information on GWG and breast-feeding was more likely among lower income women and women who were themselves obese, although the pattern was less pronounced for breast-feeding. This suggests that higher weight gain in the last pregnancy is related positively to the risk of subsequent obesity and that we have underestimated the effect for breast-feeding.
Table 3 gives the adjusted odds of obesity by maternal characteristics. As shown by model 1 ( Table 2 ), after adjustment for other characteristics, maternal age becomes a significant factor, with an increase of the odds to 47-74% as maternal age increases. On the other hand, maternal parity becomes insignificant in adjusted analyses. The reason for this is shown in the Figure , which shows the proportion of women who are obese by parity and household income. This shows differential trends in the risk of obesity with parity by level of household income. For women in the lowest 3 income quintiles, the risk of obesity increases with parity, whereas the risk falls for women in the top 2 quintiles, which yielded a zero net relationship. This pattern was adjusted for the use of interaction terms in Table 2 , model 2, which adds 5 parameters that measure the additional effect of a unit increase in parity in all other income groups relative to a unit increase in the highest income group. The significant positive effects for the interaction between parity and the 3 lowest income groups confirms the statistical relationship between parity, income, and obesity risk adjustment for other factors that is suggested by the Figure .
| Variable | Model 1 | Model 2 | ||
|---|---|---|---|---|
| Nationality | Odds ratio | 95% CI | Odds ratio | 95% CI |
| Irish | 1.00 | 1.00 | ||
| United Kingdom | 1.10 | 0.72–1.69 | 1.10 | 0.71–1.69 |
| EU12 a | 0.63 | 0.46–0.86 | 0.64 | 0.47–0.87 |
| EU14 b | 1.07 | 0.57–2.00 | 1.05 | 0.56–1.98 |
| African | 2.18 | 1.31–3.62 | 2.14 | 1.27–3.61 |
| Asian | 0.36 | 0.16–0.80 | 0.36 | 0.16–0.81 |
| Other | 1.54 | 1.16–2.05 | 1.52 | 1.15–2.02 |
| Age, y | ||||
| <25 | 1.00 | 1.19–1.95 | 1.00 | 1.12–1.85 |
| 25-29 | 1.52 | 1.22–2.00 | 1.44 | 1.14–1.87 |
| 30-34 | 1.56 | 1.12–1.91 | 1.46 | 1.09–1.85 |
| 35-39 | 1.46 | 1.32–2.58 | 1.42 | 1.27–2.49 |
| ≥40 | 1.85 | 0.94–1.07 | 1.78 | 0.56–0.89 |
| Parity | 1.00 | 1.19–1.95 | 0.70 | 1.12–1.85 |
| Current smoking | ||||
| None | 1.00 | 1.00 | ||
| Occasional | 0.91 | 0.71–1.17 | 0.92 | 0.72–1.17 |
| Light | 0.84 | 0.67–1.05 | 0.84 | 0.67–1.05 |
| Medium | 0.97 | 0.75–1.26 | 0.97 | 0.75–1.26 |
| Heavy | 1.18 | 0.94–1.48 | 1.17 | 0.93–1.46 |
| Highest level of education c | ||||
| Lower secondary | 1.78 | 1.40–2.26 | 1.75 | 1.38–2.22 |
| Upper secondary | 1.76 | 1.45–2.13 | 1.75 | 1.44–2.13 |
| After secondary | 1.53 | 1.2–1.81 | 1.53 | 1.30–1.81 |
| Third level | 1.00 | 1.00 | ||
| Household net equivalized income (quintile) | ||||
| Lowest | 2.00 | 1.56–2.57 | 1.42 | 1.04–1.95 |
| Second | 1.61 | 1.27–2.05 | 1.36 | 1.00–1.85 |
| Third | 1.39 | 1.10–1.76 | 1.10 | 0.80–1.51 |
| Fourth | 1.22 | 0.97–1.53 | 1.13 | 0.85–1.50 |
| Highest | 1.00 | 1.00 | ||
| Data missing | 1.21 | 0.90–1.62 | 0.88 | 0.59–1.30 |
| Pregnancy weight gain, kg | ||||
| <10 | 0.96 | 0.81–1.13 | 0.95 | 0.81–1.12 |
| 10-15.9 | 1.00 | 1.00 | ||
| ≥16 | 1.14 | 0.96–1.36 | 1.14 | 0.96–1.36 |
| Data missing | 1.73 | 1.43–2.08 | 1.73 | 1.43–2.08 |
| Breast-feeding, mo | ||||
| None | 1.00 | 1.00 | ||
| <1 | 0.86 | 0.68–1.08 | 0.85 | 0.68–1.07 |
| <6 | 0.81 | 0.67–0.97 | 0.80 | 0.66–0.97 |
| ≥6 | 0.65 | 0.52–0.82 | 0.65 | 0.52–0.81 |
| Data missing | 0.93 | 0.76–1.13 | 0.91 | 0.75–1.12 |
| Lowest income quintile × parity | 1.56 | 1.22–2.00 | ||
| 2nd income quintile × parity | 1.39 | 1.07–1.81 | ||
| 3rd income quintile × parity | 1.47 | 1.12–1.93 | ||
| 4th income quintile × parity | 1.19 | 0.90–1.58 | ||
| Data missing | 1.58 | 1.17–2.12 | ||
| Constant | 0.09 | 0.08 | ||
| n | 10524 | 10524 | ||
| −2 × log-likelihood | 9133.566 | 9108.755 | ||
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
