Contribution of parental blood pressures to association between low birth weight and adult high blood pressure: cross sectional study

British Medical Journal, March 14, 1998 by Brian R. Walker, Alex McConnachie, Joseph P. Noon, David J. Webb, Graham C.M. Watt

Introduction

During the past decade a series of epidemiological studies in several countries has documented that babies of low birth weight have higher blood pressure as children and adults.[1-3] These relations are maintained after correction for gestational age at birth or other influences on blood pressure in later life, including obesity, socioeconomic group, and alcohol consumption. The association between low birth weight and subsequent hypertension may be explained by inadequate fetal nutrition during pregnancy, resulting either from inadequate maternal nutrition or placental dysfunction.[4] Fetal adaptations to undernutrition are thought to programme permanent changes in factors that influence blood pressure in later life, including cortisol, growth factors, and insulin.[4] This model is supported by experiments in animals, in which manipulations in utero, including maternal undernutrition[5] and treatment with glucocorticoids,[6] result in lower birth weight, raised blood pressure, and hormonal abnormalities in the adult offspring.

Both blood pressure[7] and birth weight[8] are influenced by hereditary factors, so there may be a familial association between low birth weight and hypertension which does not depend on programming of raised blood pressure. Therefore, assessment of the parental background of people with low birth weight and subsequent hypertension is important Studies which included information about the participants' mothers have shown that maternal smoking, socioeconomic group, and anaemia did not explain the observed relations between low birth weight and subsequent high blood pressure.[9-11] Maternal blood pressure has been assessed during pregnancy, when higher pressures were associated with lower birth weight[12-14] and higher blood pressure in the offspring.[13, 15-17] Only one study has measured maternal blood pressure outside pregnancy, and this showed that higher blood pressure in 4 year old children was associated with both lower birth weight and higher maternal blood pressure.[11] To our knowledge, no study has taken account of any paternal factor other than socioeconomic group. We examined a population of young adults in whom blood pressures have been measured in both parents and sought to establish the contribution of parental blood pressure to the relation between low birth weight and subsequent hypertension.

Subjects and methods

In 1979, as part of the screening programme for the Medical Research Council's mild hypertension trial, blood pressure was measured in 6088 adults registered at the Ladywell Medical Centre in Edinburgh. In 1986, blood pressure was recorded in 864 young adults registered at the medical centre whose parents had both participated in the earlier screening programme. Some of the 864 offspring were siblings, so the cohort was drawn from 603 families. Details of these offspring and parents have been described elsewhere[7] and are shown in table 1. All blood pressures were measured in the same way: at any convenient time of day, after 5 minutes of sitting, and by two trained observers using a Hawksley random zero sphygmomanometer. The means of the two readings were used for analysis. Offspring were also weighed and their height was measured, and women were asked if they were using an oral contraceptive. Offspring from this cohort were then selected from groups with maximum contrast in their predisposition to high blood pressure--that is, on the basis of offspring and parental blood pressures being in the upper or lower third of the age adjusted distribution. Subgroups of these offspring participated in a series of further studies, which are reviewed elsewhere.[18, 19]

Table 1 Characteristics of offspring and parents in study
population. Values are means (SD) unless stated otherwise

                                   Offspring

                          This study        Whole study[7]
                           (n=452)             (n=864)

No of men                     231                 458
No of women taking
 oestrogens                   104                 203
Mean age (range)
 (years)                    21 (16-26)          21 (16-27)
Systolic blood
 pressure (mm Hg)          117 (13)            117 (13)
Diastolic blood
 pressure (mm Hg)           66 (11)             67 (11)
Body weight (kg)            65 (10)             65 (10)
Height (m)                1.70 (0.09)         1.70 (0.06)
Birth weight (g)          3470 (476)

                                     Fathers

                           This study        Whole study[7]
                             (n=452)            (n=603)

No of men
No of women taking
 oestrogens
Mean age (range)
 (years)                    45 (35-64)          46 (35-64)
Systolic blood
 pressure (mm Hg)          127 (17)            126 (18)
Diastolic blood
 pressure (mm Hg)           77 (10)             77 (10)
Body weight (kg)
Height (m)
Birth weight (g)

                                     Mothers

                           This study        Whole study[7]
                             (n=452)            (n=603)

No of men
No of women taking
 oestrogens
Mean age (range)
 (years)                    43 (34-62)          43 (34-62)
Systolic blood
 pressure (mm Hg)          120 (18)            120 (18)
Diastolic blood
 pressure (mm Hg)           74 (12)             73 (12)
Body weight (kg)
Height (m)
Birth weight (g)