Maternal Characteristics Related to Post Partum Body Composition Changes Among Lactating and Non-Lactating Mothers

A group of 32 breast-feeders and 30 bottle-feeders was followed for a six month period in order to compare their patterns of weight change after delivery. Women were recruited at the Queen Mother's Hospital in Glasgow a few days after delivery. The sample included non-obese healthy women, aged between 20 and 35 years having a singleton birth at term. Pre-pregnant weight, fat and weight gains during pregnancy were estimated from the booking weight. Anthropometric measurements including body weight, four limb circumferences and four skinfold thicknesses were carried out every two weeks for the first two months and once a month from the third to the sixth month post partum. Maternal characteristics such as pre-pregnant weight, fat and weight gains during pregnancy were similar in both groups. Breast-feeders came from a higher social class than bottle-feeders and smoking was more common among bottle-feeders. Mothers started the study at two weeks post partum with a residual weight gain (the difference between the weight at two weeks post partum and the estimated pre-pregnant weight) of 5.3 kg for breast-feeders and 5.0 kg for bottle-feeders. By the end of six months post partum, both groups had lost weight, with a total of 3.66 kg for breast-feeders and 1.98 kg for bottle-feeders. The difference between the two weight losses being statistically significant with a p < 0.01. Changes in skinfold and circumferences measurements were not statistically different between the two groups. From these measurements it appeared that fat was lost mainly over the trunk rather than over the limbs. Although weight loss was significantly different between both groups, changes in fat mass as measured by skinfolds were not statistically different. It is possible that skinfold measurements might not be sensitive enough to provide an accurate estimate of fat mass during the puerperium. Or perhaps that post partum changes in a fat-free component, the excess breast tissue deposited during pregnancy, have concealed the real changes in fat mass. An analysis of variance and a stepwise regression were carried out to identify which maternal characteristics had an influence on weight change post partum. Four factors were shown to be significant. They are in decreasing order of importance, time, residual weight gain, method of infant feeding and smoking. A total of 50.9% of the variance was explained by the presence of these factors in the analysis. The effect of residual weight gain on breast-feeders, who were almost exclusively non-smokers, and bottle-feeders non-smokers led to interesting results. As a rule, the smaller the residual weight gain, the greater the proportion of this weight that would be lost by six months post partum. The proportion of this residual weight gain lost by breast-feeders was always greater than for bottle-feeders non-smokers. The pattern of weight change among bottle-feeders smokers was erratic and therefore difficult to interpret. An equation of regression is given to predict weight loss after delivery. The type of woman having the best chances to lose all the weight gained in pregnancy by six months post partum is a breast-feeder, non-smoker who gained less than 12 kg during pregnancy