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Longitudinal changes in body composition with advancing pregnancy and the relationship of maternal fat deposition to fetal growth.

Soltani-Karbaschi, Hora (1996) Longitudinal changes in body composition with advancing pregnancy and the relationship of maternal fat deposition to fetal growth. PhD thesis, University of Sheffield.

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Abstract

Obesity has long been recognised as a risk factor for the development of variety of life threatening diseases; examples include diabetes mellitus and cardio vascular disease. In particular, in young women, it is widely thought to predispose towards impaired glucose tolerance and gestational diabetes. Obesity is not only common but it is increasing in prevalence despite the efforts made by individuals and their health advisors to avoid it. Identification of factors contributing to obesity could be useful in planning preventative policies. Many women relate the onset of their obesity to one or more of their pregnancies. We now know that there is more to obesity than the actual amount of excess weight. The adverse metabolic effects of obesity are proved to be greater when excess fat deposition is central rather than peripheral. The idea that fat deposition may be directed to different body sites with different effects on glucose tolerance and insulin levels, is a relatively new concept. The majority of investigators have focused only on the magnitude of weight changes during pregnancy and postpartum. There is not much information with regard to the compartmental changes in body composition during and after delivery. Most studies in the developed world show maternal net fat gain accompanying pregnancy. The extent to which such fat gain is physiological, and what is its beneficial effects is unknown. It is therefore important to study the impact of other factors with possible effects on fetal growth and maternal body composition. The present work examines further the question of fat storage by means of a longitudinal study to establish changes in body fat content during normal pregnancy and postpartum and also its relationship to maternal glucose tolerance, fetal metabolism, new-born anthropometry and infant growth. For this purpose, 123 women were recruited at their first visit to Antenatal Clinics of the Northern General Hospital, from which 73 completed 3 visits during pregnancy and 46 participated in the whole course of the study. Maternal anthropometry and body composition were measured at 13 (5 - 15), 24 (23 - 32) and 36 (34 - 41) weeks gestation during pregnancy and also 6 weeks and 6 months postpartum. Skinfold thickness measurements and Bio-electrical Impedance were used to assess the changes in body composition during pregnancy and postpartum. Glucose tolerance tests were performed at 28-31 weeks gestation. Insulin and/or C- peptide levels were also collected at birth and assessed later. Infant anthropometry (weight, length and head circumference) were measured at birth, 6 weeks and 6 months postpartum. The subjects were divided into four groups of under-weight, normal weight, over- weight and obese, based on their early pregnancy BMI. The statistical analyses were performed on the whole group and also the groups were then compared for the above mentioned variables. The two methods (Skinfold thickness measurements and Bio-electrical Impedance) showed a reasonable agreement in predicting the fat changes during pregnancy. A considerable variation was observed, however, between the two methods in the results of changes from early pregnancy to postpartum. Therefore, direct interpretation of skinfold thickness (which was consistent with the converted version of it to fat mass) was alone chosen to derive the conclusions During pregnancy, a formula which is corrected for hydration changes during gestation, was used to convert skinfold thicknesses to fat mass. The results confirmed that a substantial net gain of fat was made during pregnancy of which a significant amount was still retained at 6 month postpartum. Maternal weight increased (10.87 kg ± 4.67), but it reverted to the early pregnancy values by 6 months postpartum. The rate of fat and weight changes was significantly higher in the first half of pregnancy compared to later. The observed changes in maternal weight and fat mass, during pregnancy were not significantly different between the BMI groups (normal weight, over-weight and obese group). At the postpartum period, the obese group retained more of the net fat gain than the other two groups. A state of redistribution of fat tissue was observed in the subjects in particular in the obese group who had a tendency towards central fat retention. Gestational fat gain was not directly related to infant birth weight. In this well nourished population, maternal early pregnancy lean body mass (LBM) was the most significant predictor of infant birth weight. There was a positive correlation between maternal BMI and cord insulin (r=0.44, p=0.002) and/or C-peptide (r=0.33, p=0.008). In addition higher levels of insulin were observed in large for gestational age (LGA) babies in comparison with the average for gestational age (AGA) babies. These observations might have an important impact on the care of overweight women. It may be that reduction of maternal BMI in the prepregnancy period in the obese women would reduce the risk of gestational diabetes and also the rate of fetal hyperinsulinemia and macrosomia. Further investigation on this hypothesis is needed. In summary; obese women had significantly heavier babies than the normal weight women. Maternal fasting glucose was significantly correlated to infant birth weight. On the other hand, maternal fasting glucose and the level of fetal insulinisation was significantly associated with maternal early pregnancy BMI. This is likely to be a metabolic effect operating throughout gestation. What we can suggest is that , in the studies of maternal glucose metabolism and fetal growth, the confounding effects of maternal BMI should be seriously considered

Item Type: Thesis (PhD)
Keywords: Obesity
Depositing User: EThOS Import Sheffield
Date Deposited: 23 Nov 2012 16:27
Last Modified: 08 Aug 2013 08:50
URI: http://etheses.whiterose.ac.uk/id/eprint/3046

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