Key words |
| Pregnancy, weight gain, cohort study, overweight, smoking, stress |
Introduction |
| Excessive weight gain during pregnancy is an emerging health problem in developed
countries. Three studies reported that the gestational weight gain exceeded more than
the recommended range for over 50% of mothers1-3 and another study which showed
that the proportion gaining excessive weight increased from 15.5% in 1988 to 19.5%
in 2003.4 Excessive gestational weight gain results in adverse pregnancy outcomes for
both the mother and the foetus, including delivery complications. Adverse maternal
outcomes include gestational hypertension,5-7 preeclamsia,6-9 and postpartum weight
retention.10 Delivery complications include augmentation of labour,5 failed induction,8
and cesarean delivery.7-10 Adverse fetal outcomes include stillbirths,9 shoulder
dystocia,9 meconium aspiration,9 fetal distress,9 higher birthweight,5,10,11
macrosomia,10,12 large-for-gestational age infants,7-10 neonatal metabolic abnormality5
and early neonatal death.9 With regard to events related to later life, it has been
reported that children of mothers who gained more than the recommended weight
gain have a greater risk of being overweight at seven years of age13,14 than for children
of mothers who met the weight gain recommendations. In addition, overweight in
children had been shown to be associated with higher systolic blood pressure later in
life in one of these studies.13 |
| Identification of factors that are associated with excessive weight gain is important for
the prevention of adverse outcomes described above. Only a few studies have
assessed the determinants of excessive weight gain.2,3,15 and all these studies were
from developed countries. Demographic and epidemiological transition in developing
countries had led to an increase in the incidence of non-communicable diseases16 As
overweight is a known risk factor for several non communicable diseases, it is
important to determine the factors that lead to excessive weight gain during pregnancy
which may have contributory role to development of the same in later life of both the
mother and the offspring. Therefore, the objective of this study was to determine the
effect of maternal and social factors on excessive gestational weight gain. |
Methods |
| A population-based prospective cohort study was carried out in two Medical Officer
of Health (MOH) areas of a district in Sri Lanka. The latter areas are the basic health
units which provide preventive and promotive health care to the community at the
grass root level with a special focus on maternal and child health services. With
regard to antenatal services 36 clinics per month were conducted by the field staff of
the two areas for which the estimated population was 200,000 at the time of the study.
The duration of the study was one year from beginning of May 2001 to mid April
2002. All pregnant mothers eligible to participate in the study were recruited on or
before 16 weeks of gestation from filed antenatal clinics and followed up until
delivery. The exclusion criteria were pre-existing diabetes mellitus and hypertension
and multiple pregnancy. Details of this study have been published elsewhere.17 |
| The study instrument consisted of an interviewer administered questionnaire, which
included socio-demographic characteristics, information on present and past obstetric
history and physical activity. . With regard to the latter, the average number of hours
spent on standing, walking, sitting and sleeping per day by individual mother in each
trimester was inquired. For working mothers, duration of time spent on standing,
walking, and sitting per day except sleeping were asked separately for working and
non working days and a weighted average was computed. Modified Life Events
Inventory (MLEI) and the General Health Questionnaire (GHQ 30) were used to
assess the psychosocial status of the mothers. The GHQ 30 is a self-administered
questionnaire which had been validated and widely used to detect psychological
disorders. It includes 30 questions which is rated on the standard 0-0-1-1 scale and
summed up to a total. The cut off for determining case ness is a total score of 6. Sex,
age and educational level had been shown to have no significant effect on the validity
of the GHQ.18,19 and it has been recognized to be sensitive to short-tem psychological
disorders. MLEI contains a checklist of 28 items of events identified as psychosocial
stressors. MLEI has also been used by several authors to assess psychosocial stress
during pregnancy.20,21 All the questionnaires were administered at the time of
recruitment, during the second and the third trimesters. The first, second and third
trimester assessments were done on average at 12, 28, and 36 weeks of gestation. Four
trained data collectors were used for gathering information. |
| Maternal weights were measured at the first antenatal clinic visit and at delivery. The
technique of measurement was standardized and the weighing machines in the clinics
were calibrated regularly using a known weight. In addition, maternal height,
hemoglobin percentage and blood pressure measurements were carried out according
to a standard protocol to minimize inter and intra observer variations. Gestational
weight gain was calculated as the difference between maternal weight at delivery and
the first antenatal clinic visit. Excessive weight gain was defined according to the
recommendations of the Institute Of Medicine [IOM] (2009)22, in which,
categorization of gestational weight gain was based on the pre-pregnancy BMI levels.
Recommended total gestational weight gain values are respectively: underweight
(<18.5 kg/m2), normal weight (18.5 – 24.9 kg/m2), overweight (25.0 – 29.9 kg/m2),
and obese (≥30.0 kg/m2) are 12.5 – 18.0 kg, 11.5 – 16.0 kg, 7.0 – 11.5 kg, and 5.0 –
9.0 kg,.22 BMI was determined based on the weight and height measurements of the
first antenatal clinic visit. |
| Passive smoking was defined as exposure to someone else’s cigarette smoke, whether
at home or at work, and alcohol consumption as the consumption of any type of
alcohol during pregnancy. Educational status of the mother was defined as the highest
received educational level. Per-capita monthly income was determined by the total
disclosed family income divided by the number of family members. Maternal
complications were defined as bleeding during antenatal period, or the presence of
pregnancy induced hypertension or gestational diabetes. Median duration of each
posture adopted /day was taken as the cut off level for the final analysis. |
| The SPSS version 16 was used for data analysis. Bivariate logistic regression was
carried out to determine the odds ratio (OR) for excessive weight gain in terms of each of the socio-demographic and maternal variables and for trimester specific
exposures. Unconditional multiple logistic regression was carried out to control for
the confounding factors. Eligibility for including the variables into the regression
model was based on statistical criteria (p-value <0.25) as well as biological
plausibility.23 The eligible socio-demographic, maternal and trimester specific
exposure variables included were coded as zero and one. The initial model contained
all the variables and it was modified by concurrent addition and deletion of variables
until the most suitable model was accomplished.23 The number of mothers included in
the final regression model was 574. The number of events per variable was 7.4.
Interactions between each individual variable in the final model were tested which
were not found to be statistically significant. No collinearity between variables was
evident. |
| Informed consent was obtained from individual participants and ethical approval
granted by the Ethics Review Committee of the Faculty of Medicine, University of
Kelaniya, Sri Lanka. |
Results |
| The total number of women who attended the clinics during the reference period was
942. Twelve refused to participate with a non participation rate of 1.3%. Of the
remaining 930, 45 were not eligible (4.7%) and therefore the total recruited was 885.
Fifty six mothers were excluded from the analysis due to multiple pregnancy (11) and
fetal death (45). Of the remaining 829, 119 (14.4%) were excluded from the analysis
due to non-availability of weight measurements at the booking visit or at the final
assessment. The final sample included in the first trimester analysis was 710, having
completed all the exclusions described above. |
| The mean age of the mothers was 26.4 (SD 5.5) years of which 757 (91%) were in the
age group of 18 to 35 years. Twenty five percent (n=203) had an educational level
above grade 10 and 5% (n=40) up to grade five. Three hundred and eighty nine (47%)
mothers were primiparous, and six mothers (0.7%) grand multiparous. Two hundred
and ten (29.6%) had a BMI of <18.5 kg/m2 and 114 (16%) a BMI of >25 kg/m2. Total
mean weight gain was 10.6 (SD 3.3) kg. Of the 710, 62 (8.7%) women gained more
weight than IOM recommendations. Nineteen (5%) among normal weight mothers
(BMI of >18.5 – 24.9 kg/m2) and 39 (34%) among overweight/ obese mothers
(BMI≥25 kg/m2) had excessive gestational weight gain. |
| Eighty four mothers (12%) during the second and 132 (18.6%) during the third
trimesters had not attended the routine antenatal clinics. Therefore only 626 mothers
for the second and 578 for the third trimester were left for the analyses. Of the 626
mothers who participated during the second trimester and 578 mothers in the third
trimester, 57 and 52 had excess gestational weight gain respectively. |
| Compared to the mothers who did not exceed recommended weight gain mothers with
excess gestational weight gain were younger (16% vs 28%) which had a statistically significant difference. The mothers with excess weight gain had higher per-capita
monthly income (85.5% vs 73%), weight >52 kg (79% vs 30%), BMI >23 kg/m2
(63% vs 11.6%), and more maternal complications (16% vs 3.4%) than the control
group and all these differences were statistically significant. Although the mothers
with excess weight gain had lower educational levels than the control group (10% vs
4.5%) the difference was not statistically significant. All the mothers with excess
gestational weight gain were not anaemic compared to the control group. |
| Mothers who experienced more than two life events during the first trimester were
27% (n=17) compared to the control group (19%; n=123) but this difference was not
statistically significant (Table 2). Proportion of mothers who sleep ≤ 8 hours/day was
more than in the control group (37% vs 33.6%) during the first as well as in the third
(19% vs 16.6%) trimester (Tables 2 and 4). A lower percentage of mothers with
excess weight gain than that of the control group were exposed to passive cigarette
smoke during the second (7% vs 11.6%) and third (02% vs 10%) trimesters (Table 3
and 4). However, none of these differences were statistically significant. |
| Multivariate analysis revealed a 4.2 fold increased risk for school educational level of
grade ≤5, a 2.7 fold increased risk for per-capita monthly income ≥1500 Rupees, a 9.0
fold increased risk for BMI ≥23 kg/m2 in relation to excess weight gain compared to
the control group after controlling for the period of gestation (Table 5). Further, the
mothers who had complications during pregnancy had a 3 fold increased risk of
excess weight gain in comparison those without complications. Mothers who were
exposed to passive cigarette smoke during the third trimester had a 88% decreased
risk of excess weight gain after controlling for the potential confounding factors
(Table 5). |
Discussion |
| Our study revealed that overweight, maternal complications during pregnancy,
passive smoking during third trimester and low educational level were determinants of
excessive weight gain after having controlled for the gestational duration. |
| We could not find any other studies that assessed the effect of passive cigarette
smoking for excessive weight gain. All the participants in our study were nonsmokers.
Several studies24,25,26 assessed the effect of active cigarette smoking for
excessive weight gain and found that it had a negative association with gestational
weight gain. In contrast to the findings of the above studies, two US based cohort
studies reported by Brawarsky2 and Chasan-Taber3 found that cigarette smoking had
no significant association with excessive weight gain. |
| Carbon monoxide in the cigarette smoke binds to hemoglobin and forms
carboxyhemoglobin. This reduces the quantity of hemoglobin in the blood, thereby
causing anaemia.27 A developing fetus, thus deprived of adequate oxygen, is exposed
to an increased risk of perinatal mortality.27,28 |
| As Asian populations were observed to have higher cardiovascular risk status than the
Western populations at any given BMI level30, the BMI cut-off points for overweight
and obesity of Asian populations were revised by the World Health Organization
(WHO).29 The study supported the use of BMI ≥25.0 kg/m2 as a new cut-off point for
obesity and a BMI of 23.0-24.9 kg/m2 for overweight30 which is lower than that
recommended for Western populations. According to our findings, overweight and
obese women (≥23 kg/m2) defined using the above cut-off values were more likely to
gain excess weight during pregnancy. Our results were consistent with the findings
reported by both Brawarsky2 and Chasan-Taber.3 |
| Several studies had found that excessive weight gain was associated with gestational
hypertension5-7 or preeclamsia.6-9. According to our study too, maternal complications
during pregnancy were observed to be associated with excessive gestational weight
gain. However, for the purpose of this study, bleeding during antenatal period,
preeclampsia, and gestational diabetes mellitus were categorized together as maternal
complications due to the inadequate sample size for separate analysis. |
| Low education of the women had a higher risk for excessive weight gain. Our results
were consistent with the findings of a US based larger study, including secondary
data, reported by Howie.31 In contrast, several studies2,3,25 had failed to report any
association between educational level and excessive weight gain. This may be
attributed to the use of different cut-off values for categorizing educational
achievements in the studies. Possibly, a low level of education deprives people of
access to necessary information on healthy life styles as well as making them less
attentive to heeding the advice of experts. Indeed, in Sri Lankan culture, pregnant
women are encouraged to consume more food in order to meet with demands of the
developing fetus. |
| According to our study, higher income levels were associated with excessive weight
gain. Our results were consistent with the findings of the study reported by Hickey24
and Rodrigues25 who found that higher income levels were positively associated with
weight gain. The former study24 was a review and the latter a cohort study25
conducted in another developing country. In contrast, Chasan-Taber3 had reported that
income was not associated with excessive gestational weigh gain. |
| We were not able to observe any association between physical activity in terms of
duration of walking and standing per day during pregnancy and excessive weight
gain. Our findings are consistent with that of three other studies 2,3,25 which reported
similar findings. In contrast to the above, Löf 15 had reported a significant association
between excessive gestational weight gain with low pre-pregnancy physical activity
level. |
| We were neither able to demonstrate an association between psychosocial stress and
excessive gestational weight gain. Psychosocial stress was assessed by administering
GHQ 30 and MLEI. Our findings were consistent with the findings of Brawarsky2 and
Chasan-Taber3. These authors too have used the same instruments as ours to assess
psychosocial stress. |
| We defined excess gestational weight gain based on IOM 2009 recommendations,
which is based on the WHO cut-off points for BMI categories.17 The other studies
described above2,3 were based on the IOM 1990 recommendations which defined
underweight as a BMI of <19.8 kg/m2 and overweight as >26 kg/m2. Therefore direct
comparisons of results are not possible. |
| Being a cohort study, loss to follow up was a major limitation of this study. However
the attrition rate was in the acceptable range and would not considerably affect either
the internal or the external validity. Although this was a follow up study, the exposure
statuses were determined on a trimester specific basis by asking participants to recall
exposures within the most recent past three months. Therefore, there was still a
minimal chance for recall bias to occur. Ideally, the participants would have been
required to maintain a diary. However, this step was purposely omitted in order to
avoid undue taxing of the participants. Despite above such inevitable limitations,
assessment of the exposure status on trimester specific basis could be considered as a
strength of our study. |
| In conclusion, being overweight or obese, earning a higher income, passive smoking
and low educational level were determinants of excessive weight gain during
pregnancy. Therefore, we would recommend better health education and closer
follow up of mothers with high BMI, especially for high income families with a low
educational background. |
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