Reproduction and Health: Obesity, Diabetes, Cardiovascular Diseases, and Osteoporosis
Reproduction requires not only additional energy but also nutrients. In addition, physiological and metabolic adjustments (e.g., immunological and increased oxidative stress) associated with pregnancy may cause permanent changes in the maternal organism, especially when pregnancies are numerous. Self-reported health status, a reliable predictor of mortality (Idler and Benyamini 1997), is lower for women with at least three pregnancies and especially for women with six or more pregnancies (Kington et al. 1997). Parity is positively related to the risk of obesity, impaired glucose tolerance, non-insulin-dependent diabetes, and cardiovascular diseases.
Cardiovascular Diseases, Diabetes, and Obesity
Many studies suggested that high parity is related to increased risk of cardiovascular diseases. The longitudinal Framingham Heart Study and the National Health and Nutrition Examination Survey documented a positive relationship between the number of pregnancies and the subsequent development of cardiovascular disease (Ness et al. 1993). In British women with at least two children, each additional child increased the risk of coronary heart disease by 30 % (Lawlor et al. 2003). In a population-based cohort Swedish study, women with five children had about 50 % higher risk of cardiovascular disease than women with two children (Parikh et al. 2010). Having gone through six or more pregnancies increased the woman’s risk of all types of strokes by 70 % (Qureshi et al. 1997).
The risk of diabetes may increase with parity as well. Among rural Australian women, those with five or more children had 28 % higher risk of diabetes than women with three or four children and 35 % higher risk than women with one or two children (Simmons et al. 2006). In Finnish women, parity of five or higher was related to 42 % higher risk of diabetes compared to the average risk experienced by women in this population (Hinkula et al. 2006). In Brussels, both parity and early age at first birth were associated with diabetes-related mortality in women (Vandenheede et al. 2012).
Pregnancy is a risk factor for obesity, and postpartum weight retention occurs in 60-80 % of women (Martin et al. 2014). In a study of the US women, each birth was associated with a 0.55 kg of permanent increase in body weight (Brown et al. 1992), while other studies reported that maternal body weight increased by 0.4-3.0 kg after each pregnancy (Harris and Ellison 1997). Among women with parity of three or more, a higher proportion was overweight than in women with lower parity. In women from Utah, a dose-response relationship was observed between the number of children and risk of obesity (Bastian et al. 2005): each additional live birth increased the risk of obesity by 11 %. In a study based on data from 65 countries, sustained breast-feeding contributed to reduction of postpartum BMI but not among relatively wealthy women (Hruschka and Hagaman 2015).
In women from developing countries, however, repeated reproductive events cause a reduction of body weight. The “maternal depletion syndrome” refers to the long-term negative changes in the maternal nutritional status, as opposed to the short-term changes associated with a single pregnancy or breast-feeding (Winkvist et al. 1992). In Papua New Guinea, the nutritional status of women decreased with parity (Garner et al. 1994). This maternal depletion occurred even though birth intervals were relatively long (3 years on average) in this population. In Turkana from northwestern Kenya, women from both nomadic and settled populations had parity-related decline in fat reserves (Little et al. 1992). In another African population, the !Kung San, the higher number of surviving children was related to lower body weight in women, while in men those with more surviving children had higher body weight (Kirchengast 2000).
Improvement in socioeconomic status seems to increase the maternal ability to resist the stress of repeated reproductive events. In Papua New Guinea, the decline in nutritional status was substantial in women who were foraging horticulturalists, while such changes were not observed among wage earners (Tracer 1991). Toba women from Argentina, a well-nourished population undergoing a transition from semi-nomadic hunter-gatherer to a sedentary, peri-urban lifestyle, did not lose excess weight gained during pregnancy despite prolonged and intense breastfeeding (Valeggia and Ellison 2003).