Weight change in the postpartum period is a dominant concern of new mothers.¹ Post-partum weight retention has important public health implications as well, because retention of gestational weight can be a significant contributor to long-term obesity and associated health risks.² Family physicians should be aware of normal postpartum weight loss patterns, as well as risk factors for weight retention, so they can assist their patients in achieving a healthy postpartum weight.

Normal Postpartum Weight Loss Patterns

The greatest amount of weight loss occurs in the first three months postpartum and then continues at a slow and steady rate until six months postpartum.^3–5 Studies relating lactation to postpartum weight loss have revealed inconsistent results, although most studies do not support the notion that breastfeeding accelerates postpartum weight loss or leads to less weight retention.^3,5–9

Some investigators suggest that breastfeeding mothers may not lose as much weight as expected because the Recommended Daily Allowance (RDA) for lactating women of 2,500 kcal per day is too high and does not take into account the fact that most women who lactate are relatively sedentary. Recent research suggests that lactating women may more easily lose weight without diminishing their milk supply if their kcal intake per day is between 2,000 and 2,300.^4,5

A recent prospective trial¹⁰ of 21 overweight, exclusively breastfeeding women found that caloric restriction by 500 kcal per day and 45 minutes of exercise per day, four days a week, resulting in a weight loss of approximately 0.5 kg per week between four and 14 weeks postpartum, did not affect the growth of their infants when they were compared with a control group who neither restricted calories nor exercised more than once a week.

Risk Factors for Weight Retention

Besides lactation, factors such as pre-gravid weight, gestational weight gain, age, parity, race, smoking status, exercise history, marital status, and employment have been investigated for a relationship to postpartum weight loss.^3,7–9 Of these factors, weight gain during pregnancy is the one that has proved in multiple studies to be the most relevant.^{2,4,6–9,11–13}

The Institute of Medicine (IOM)¹⁴ recommends that women with a normal pre-gravid body mass index (BMI) of 19.8 to 26 should gain 11.5 to 16 kg during pregnancy; underweight women (BMI of less than 19.8) should gain 12.5 to 18 kg; overweight women (BMI of 26 to 29) should gain 7 to 11.5 kg; and obese women (BMI of greater than 29) should gain 6 kg.

In a 1995 prospective study¹¹ of 274 patients with a normal pre-gravid BMI, 28 percent had excessive gestational weight gain (more than 0.68 kg per week at 20 to 36 weeks, or 20 kg total), retaining about 40 percent of the gestational weight at six months postpartum. This yielded an odds ratio of 2.9 for being overweight (BMI greater than 26) at six months postpartum.

Adolescent and black patients are at higher risk for postpartum weight retention. It is common for growing adolescent mothers to gain an excessive amount during pregnancy and to retain more of the weight into the early postpartum period than nongrowing adolescents.¹²

A study² examining the implications of the IOM recommendations for 1,592 patients found that black women retained significantly more weight than white women with comparable weight gain during pregnancy. The higher rate of excessive weight gain in pregnancy and failure to return to pre-gravid weight postpartum may partially explain the higher prevalence of obesity and obesity-related illnesses in women of these two patient populations.^11,15

Achieving a Healthy Postpartum Weight

Family physicians should counsel their patients during pregnancy about the risks of excessive weight gain and subsequent obesity. Gestational weight gain in excess of current IOM recommendations (even in patients with a normal pre-gravid BMI) can lead to significant postpartum weight retention, especially in growing adolescents, minorities, and low-income patients.

Family physicians can help patients develop realistic weight loss goals in the postpartum period and beyond, emphasizing that post-partum weight loss normally proceeds slowly and steadily. Lactation may not facilitate weight loss, especially if the patient consumes a high-calorie diet and does not routinely exercise for an adequate amount of time.