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Obesity, Diabetes and the Risk of Macrosomia
LGA infants, although this may be attributed to the relatively small sensitivity was reported to be one of the strongest correlates with
sample size in this study.
Several studies found that other measures of foetal growth, in particular fat mass at birth.
Moreover, it is well
obesity (rather than pre-pregnancy BMI) were associated with established that foetal overgrowth is associated with glycaemic control
exaggerated foetal growth. In a recent retrospective study of 233 during the first trimester,
although some have found that it is
women with gestational diabtes, maternal weight at delivery was the hyperglycaemia during the third trimester that increases the risk of
only factor that was significantly associated with LGA infants.
As yet, the mechanisms by which insulin resistance
in a case-control study of women without diabetes, birthweight prior to affects foetal growth are not well defined, but may involve altered
delivery was the strongest predictor of macrosomia.
Pre-pregnancy placental function in addition to increased foeto-placental availability of
weight was also found to be correlated with neonatal weight.
nutrients in late gestation.
Foetal growth is also influenced by the location of body fat stores in Apart from the risk of macrosomia, diabetes and insulin resistance may
Brown et al. investigated the influence of regional also be manifested as an increase in fat mass, even when foetal weight
distribution of fat on newborn size. WHR ratio was found to be an is in the normal range.
Interestingly, Catalano et al. found that while
independent predictor of neonatal weight; each 0.1-unit increase in insulin sensitivity in late gestation correlated best with newborn weight
pre-gravid WHR ratio predicted a 120g greater birthweight.
Thus, it and fat-free mass, the best correlate with neonatal fat mass was insulin
appears that being obese or overweight is an independent risk factor sensitivity prior to conception.
for macrosomia, and the risk is proportional to the level of obesity. The
mechanism by which obesity affects neonatal birthweight is unclear. Obesity or Diabetes – Which Is Worse?
Possible explanations include obesity-related insulin resistance
and A number of studies have tried to determine which of these two factors,
The co-presence of undetected type 2 diabetes or obesity or diabetes, is more important in the pathogenesis of foetal
GDM, both of which have been shown to be associated with overgrowth and macrosomia, but results are conflicting. Several studies
is another possible explanation. have suggested that obesity plays a more important role than impaired
glucose tolerance (IGT) or diabetes during pregnancy. In a study of 300
Weight Gain During Pregnancy women who underwent a 75g oral glucose tolerance test (OGTT)
and Birthweight following an abnormal 50g glucose challenge test (GCT), the correlation
Apart from pre-gravid maternal obesity, weight gain during pregnancy of pre-pregnancy weight and pregnancy weight gain with birthweight
has also been reported to be an independent risk factor for percentile was higher than that of the fasting and two-hour OGTT
In a recent prospective study of 631 pregnancies, values.
In a large prospective cohort study of women without diabetes
pregnancy weight gain was the most important correlate with who were screened for GDM by GCT, Yogev et al. found on multivariate
In another study of women with varying levels of glucose analysis that maternal obesity, but not the GCT result, was a significant
intolerance, pregnancy weight gain was found to be at least as predictor of macrosomia (OR 2.9). Similarly, in a case-control study of
important as glycaemic control in affecting birthweight.
Furthermore, macrosomic infants of non-diabetic mothers, birthweight prior to
Ray et al. calculated that for each 5kg increase in weight during delivery was the strongest predictor of macrosomia, while abnormal
pregnancy, the risk of a LGA infant increased by 30%.
GCT result was the least significant factor.
Hutcheon et al. retrospectively studied 90 women who had at least two However, it could be argued that merely the presence of glucose
pregnancies complicated by GDM in order to assess the effect of obesity intolerance of any degree is not an appropriate measure for
and diabetes on foetal growth within the same subject. They found that evaluating the contribution of diabetes to foetal growth, since most of
weight gain during pregnancy was the only factor that affected neonatal these studies lacked information regarding glucose levels and degree
birthweight within the same woman.
of glycaemic control.
Nevertheless, other studies found maternal
obesity to be a more important predictor of neonatal birthweight,
The timing of weight gain during pregnancy is also of importance. In a even when considering plasma glucose levels. In a prospective,
prospective study of 389 uncomplicated pregnancies, weight gain population-based study of 2,272 women with GDM, maternal weight
during the first trimester was the best predictor of neonatal weight at delivery was the only significant predictor of birthweight percentile,
(31g for each 1kg maternal weight gain), followed by weight during the whereas the predictive value of plasma glucose levels was poor. The
second trimester (26g per 1kg). Weight gain during the third trimester authors concluded that factors associated with maternal obesity in
was not associated with newborn weight. However, several studies well-controlled GDM may be more significant than glucose control in
found weight gain to have little (OR 1.08)
or no effect
on the risk the development of LGA infants.
This was also found to apply to
of macrosomia. Thus, the effect of weight gain during pregnancy on women with PGDM. In a retrospective study of women with PGDM
neonatal birthweight remains controversial, and its contribution to and GDM, birthweight closely paralleled pre-pregnancy BMI rather
foetal overgrowth is probably less important than that of maternal than glycaemic control.
In contrast, others have found diabetes to be more important than
Diabetes and Birthweight maternal obesity in the prediction of foetal macrosomia.
The association between diabetes, either PDGM or GDM, and foetal retrospective cohort study, maternal BMI and GDM were independent
macrosomia is well established,
and even minor degrees of risk factors for macrosomia, but GDM seemed to play a more
glucose intolerance have been shown to be associated with increased important role.
In another study of 90 women with diabetes, the
Several studies reported that PGDM is association between birthweight and third-trimester glucose levels
associated with a higher risk of macrosomia than GDM.
In was higher than that with pre-pregnancy BMI.
concordance with these studies, decreased maternal pre-gravid insulin have found that it is only the presence of glucose intolerance that
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