Women assigned to the Balance after Baby program ( n = 36 , three lost to follow-up ) lost a mean of 2.8 kg ( 95 % confidence interval -4.8 to -0.7 ) from 6 weeks to 12 months postpartum , whereas the control group ( n = 39 , one lost to follow-up ) gained a mean of 0.5 kg ( -1.4 to +2.4 ) ( P = .022 ) .