Summary
Hypertension is becoming an important health problem in many countries. The ‘small baby syndrome hypothesis’ suggests that an inverse linear relationship exists between birth weight and later risk of hypertension; however, this relationship is under debate. We conducted a meta-analysis to examine the association between birth weight and subsequent blood pressure. Among 78 studies reporting on the association between birth weight and subsequent blood pressure, 20 articles (reporting 27 original studies) were eligible for inclusion. Low birth weight (< 2500 g) compared with birth weight greater than 2500 g was associated with an increased risk of hypertension (odds ratio [OR] 1.21; 95% confidence interval [CI] 1.13, 1.30); high birth weight (> 4000 g) compared with birth weight less than 4000 g was associated with a decreased risk of hypertension (OR 0.78; 95% CI 0.71, 0.86). When low birth weight (< 2500 g) was compared with birth weight greater than 2500 g, mean systolic blood pressure (SBP) increased by 2.28 mmHg (95% CI 1.24, 3.33); when high birth weight (> 4000 g) was compared with birth weight less than 4000 g, mean SBP decreased by 2.08 mmHg (95% CI –2.98, –1.17). These findings indicate that there is an inverse linear association between birth weight and later risk of hypertension, and that this association primarily exists between birth weight and SBP.
Résumé
L’hypertension artérielle est un problème de santé publique intéressant de nombreux pays dans le monde. L’hypothèse du syndrome du petit bébé suggère une relation inverse entre le poids à la naissance et le risque ultérieur d’hypertension artérielle. Cependant, cette hypothèse reste controversée. Nous avons réalisé une méta-analyse examinant l’association entre le poids à la naissance et la pression artérielle lors de la vie. Parmi 78 études rapportant une association entre poids à la naissance et pression artérielle, 20 articles rapportant 27 études originales ont été considérés dans cette méta-analyse. Un poids à la naissance inférieur à 2500 g comparé à un poids à la naissance supérieur à 2500 g est associé à une augmentation de risque d’hypertension artérielle ( odds ratio 1,21 ; intervalle de confiance [IC] 95 % 1,13–1,30) ; un poids à la naissance supérieur à 4000 g comparé à un poids à la naissance inférieur à 4000 g est associé avec une diminution du risque d’hypertension artérielle ( odds ratio 0,78 ; IC 95 % 0,71–0,86). Lorsque le poids à la naissance est inférieur à 2500 g, comparativement à un poids à la naissance supérieur à 2500 g, la pression artérielle systolique moyenne augmente de 2,28 mmHg (IC 95 % 1,24–3,33) ; lorsque le poids à la naissance est supérieur à 4000 g, comparativement aux sujets dont le poids à la naissance est inférieur à 4000 g, la pression artérielle systolique moyenne diminue de 2,08 mmHg (IC 95 % –2,98, –1,17). Ces observations issues de cette méta-analyse indiquent qu’il existe une association linéaire inverse entre le poids à la naissance et le risque ultérieur d’hypertension artérielle et cette association concerne en particulier le poids à la naissance et la pression artérielle systolique.
Introduction
Hypertension is one of the most important risk factors for CVD and the second leading cause of death in China . In China, people with hypertension were five times more likely to develop stroke than those with normal blood pressure . In Western populations, 30% of total mortality attributable to CVD could be prevented if blood pressure could be reduced by 10 mmHg . Although extensively studied, the aetiology of hypertension cannot be fully explained by genetic factors and adulthood risk factors, such as age, body mass index, physical activity and cigarette smoking . It has been suggested that factors related to the intrauterine and postnatal environments may contribute to the development of hypertension . Intrauterine development may ‘programme’ foetal anatomy, physiology and metabolism, and thus may affect the risk of diseases, including hypertension, in later life . This hypothesis has been evaluated in animal models and low birth weight (BW) or intrauterine nutrition deficiency was found to be associated with high blood pressure and/or resulted in adult hypertension .
Barker et al. have suggested that there may be developmental periods in utero and in infancy during which inappropriate nutrition and poor growth lead to long-term consequences for adult CVD . Blood pressure in adults is typically inversely associated with BW . This inverse relationship has also been described in childhood, once adjustment is made for current size . Subsequently, a number of studies found an association between low BW and increased risk of adult hypertension. Most researchers claimed that babies who were born short and thin had an increased risk of hypertension in subsequent life .
Many authors have claimed that the relationship between BW and later blood pressure is inversely linear , which implies that high BW would lead to a decreased risk of hypertension. However, some researchers found that BW had little effect on subsequent blood pressure or found an increased risk of hypertension in subjects with low BW and those with high BW . Some studies that found an inverse linear association between BW and subsequent blood pressure used a classification of BW that differed to that in the present study. In one meta-analysis by Huxley et al. , mean BW was used. We divided BW into less than 2500 g versus greater than 2500 g and greater than 4000 versus less than 4000 g, thus performing a meta-analysis with a different classification to further validate the relationship between BW and subsequent blood pressure.
Methods
Literature search strategy
PubMed and ScienceDirect databases were searched for articles published between 1995 and 2011. We used the terms ‘birth weight’, ‘intrauterine growth restriction’, ‘hypertension’, ‘blood pressure’, and ‘cardiovascular diseases’ in the full-text option. Furthermore, we manually searched all references cited in the original studies and reviews identified. In total, 78 studies reported on the association between BW and subsequent blood pressure.
Studies included and excluded criteria
To be eligible, a study had to fulfil the following criteria: it had to be an original report on the relationship between BW and blood pressure; and odds ratios [ORs] and 95% confidence intervals [CIs] (or the data with which to calculate them) for hypertension or blood pressure values had to be presented. Alternatively, BWs could be reported as categorical data with a certain range (e.g., < 2500 g, > 2500 g, > 4000 g, < 4000 g, etc.). Papers were excluded for the following reasons:
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if the title and abstract clearly did not contain data on BW and hypertension or blood pressure;
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if there were insufficient dichotomous data on BW and hypertension or blood pressure;
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duplicate;
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if there was no measure of BW;
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if the paper was a review or commentary article;
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if the paper reported data using different BW categories.
Quality assessment
The Newcastle-Ottawa quality assessment scale was used for quality assessment . Ten questions were assessed and each satisfactory answer received 1 point, resulting in a maximum score of 10. Only studies for which the majority of questions were deemed satisfactory (i.e. with a score of 6 or higher) were considered to be of high methodological quality.
Assessment of heterogeneity
The chi-square test was used to test for heterogeneity across studies. A random-effects model was used to account for possible heterogeneity between studies, which defaulted to a fixed-effects model approach in the absence of heterogeneity . A P value < 0.05 was considered significant.
Statistical analysis
Statistical analysis was conducted using Review Manager, version 5.0 (Nordic Cochrane Centre, Copenhagen, Denmark). ORs were pooled for dichotomous outcomes from each study, Means ± standard errors were pooled for continuous variables from each study and the 95% CI for each outcome was estimated to reflect the uncertainty of point estimates. Sensitivity analysis was performed to determine whether differences in statistical methods, study design, sample size and quality grade of the study affected study conclusions. Publication bias was assessed by inspection of the funnel plot and by formal testing for funnel plot asymmetry using Begg’s test and Egger’s test . These calculations were carried out using Stata/SE, version 10 (Stata Corp., College Station, TX, USA).
Results
Overview of studies included in the systematic review and meta-analysis
Among 78 studies reporting on the association between BW and subsequent blood pressure, the following were excluded for the following reasons ( Fig. 1 ): title and abstract clearly did not contain data on BW and hypertension or blood pressure ( n = 24); did not provide sufficient dichotomous data on BW and hypertension or blood pressure ( n = 12); duplicates ( n = 5); no measure of BW ( n = 7); reviews or commentary articles ( n = 7); reported data using different BW categories ( n = 3). A total of 20 original articles reporting 27 original studies were identified (one article described six studies and one article described three studies); the studies comprised 14 cohort studies , four case-control studies and two cross-sectional studies . Study characteristics are displayed in Table 1 .
| Study | Country | Study design | Year of study baseline | Total number of subjects | Age (years) | Race | BW ascertainment method | BW reference category for adjusted estimate | Outcome |
|---|---|---|---|---|---|---|---|---|---|
| Tamakoshi et al. 2006 | Japan | Cohort | 2002 | 2303 men, 804 women | 33–66 | Yellow | Questionnaire | < 2500 g; 2500–3500 g; > 3500 g | Hypertension; BP |
| Lurbe et al. 2001 | Spain | Cohort | 369 women | 4–18 | White | Recorded from medical records | < 2500 g; 2500–2999 g; 3000–3299 g; 3300–3599 g | BP | |
| Eriksson et al. 2000 | Finland | Cohort | 1924–1933 | 975 men, 983 women | 6–16 | White | Recorded from medical records | < 2500 g; 2500–3000 g; 3001–3500 g; 3501–4000 g; > 4000 g | Hypertension |
| Hardy et al. 2003 | England | Cohort | 1946 | 2815 men, 2547 women | 36–53 | White | Interview | < 2500 g; 2500–3000 g; 3001–3500 g; 3501–4000 g; > 4000 g | BP |
| Fallkner et al. 2004 | USA | Cohort | 1988 | 133 men, 117 women | 11–14 | White, Black, Hispanic, Asian | Recorded from medical records | < 2500 g; > 2500 g | BP |
| Bergvall et al. 2007 | Sweden | Cohort | 1926–1958 | 15 | White | Questionnaire | < 1999 g; 2000–2499 g; 2500–2999 g; 3000–3499 g; ≥ 3500 g | Hypertension | |
| Barker et al. 2002 | Finland | Cohort | 1933–1944 | 4627 men, 4130 women | 12 | White | Recorded from medical records | < 3000 g; 3000–3500 g; 3500–4000 g; > 4000 g | Hypertension |
| Yliharsila et al. 2003 | Finland | Cohort | 1924–1933 | 7707 men, 8558 women | 70 | White | Recorded from medical records | < 2500 g; 2500–3000 g; 3000–3500 g; 3500–4000 g; > 4000 g | Hypertension |
| Yarbrough et al. 1998 | USA | Cohort | 1984 and 1987 | 303 women | 50–84 | White | Questionnaire | Three predefined BW categories in pounds | BP |
| Kistner et al. 2000 | Sweden | Case-Control | 1970 and 1974 | 50 women | 18 | White | Recorded from medical records | Percentile for gestation | BP |
| Wei et al. 2003 | China | Case-control | 1992–1997 | 198 men, 231 women | 6–18 | Yellow | Telephone, questionnaire | < 2500 g; 2500–2999 g; 3000–3499 g; 3500–3999 g; > 4000 g | BP |
| Tian et al. 2006 | China | Cross-sectional | 1992 | 373 men, 600 women | 46.2 | Yellow | Questionnaire | < 2500 g; 2500–2999 g; 3000–3499 g; 3500–3999 g; > 3500 g | Hypertension; BP |
| Pyhala et al. 2009 | Finland | Case-control | 35 men, 46 women | 23.1 | White | Recorded from medical records | < 2500 g; > 2500 g | BP | |
| Jarvelin et al. 2004 | Finland | Cohort | 1966 | 2858 men, 3102 women | 31 | White | Questionnaire | < 2500 g; 2500–2999 g; 3000–3499 g; 3500–3999 g; 4000–4499 g; ≥ 4500 g | BP |
| Liew et al. 2008 | USA | Cohort | 1987–1989 | 5–72 | White | Interview | < 2500 g; 2500–2999 g; 3000–3499 g; 3500–3999 g; 4000–4499 g; ≥ 4500 g | BP | |
| Koupil et al. 2005 | Sweden | Cohort | 1970 | 736 men | 70 | White | Recorded from medical records | 1400–3290 g; 3300–3600 g; 3610–3960 g; 3970–5400 g | BP |
| Liew et al. 2008 | USA | Cohort | 1987–1989 | 4286 men, 5444 men | 45–64 | Black, White | Interview | < 2500 g; 2500 – 4000 g; > 4000 g | Hypertension; BP |
| Salgado et al. 2009 | Brazil | Case-control | 33 men, 35 women | 8–11 | Black | Recorded from child’s health card | ≤ 2500 g; ≥ 2500 g | BP | |
| Hirschler et al. 2008 | USA | Cross-sectional | 2006–2007 | 511 men, 516 women | 10 | White | Recorded from medical records | < 2500 g; 2500–4000 g; > 4000 g | SBP |
| Zhao et al. 2002 | China | Cohort | 1997–2000 | 75049 women | 40–70 | Yellow | Interview | < 2500 g; 2500–3249 g; 3250–3999 g; > 4000 g | Hypertension |
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