Question

Pregnant women with gestational diabetes mellitus (GDM) are at risk for long term weight gain and subsequent development of type II diabetes. A pilot weight loss clinical trial was conducted where women with GDM were randomized to either an active intervention using a web-based delivery or control intervention. Women were randomized at 6 weeks postpartum and then were seen at follow up visits at 6 months and 12 months postpartum. At 12 months postpartum, women in the active group lost a mean of 0.2lb with a standard deviation of 15.4lbs. (Ref: Nicklas JM et al., Obstet Gynecol. 201, 124(3):563-70. A web-based lifestyle intervention for women with recent gestational diabetes mellitus: a randomized controlled trial.

At 12 months after postpartum, women in the control group gained a mean of 7.9 lb with a standard deviation of 15.3 lbs compared to their pregnancy weight.

Officials in the State Helth Department are considering using the active intervention in the general population of women with GDM. However, they expect that 80% of the women who are offered the intervention will actualy comply with the intervention and are expected to have a weight gain distribution similar to the active group. The remaining 20% of women will lose interest and are expected to have a weight gain distribution similar to the control group.

Question: What % of the GDM women in the program will be expected to be no more than 2 lbs. above their pre-pregnancy weight?

Answer 1

In the active group, the percentage of women with weight above no more than 2 lbs is

In the control group, the percentage of women with weight above no more than 2 lbs is

$P(X<2)=P(Z<\frac{2-7.9}{15.3})=P(Z<-0.3856)=0.3499$

Hence the % of the GDM women in the program will be expected to be no more than 2 lbs. above their pre-pregnancy weight = 0.8*0.6025+0.2*0.3499 =0.5520