slow rising hcg levels

My hcg levels were 3.1 when tested on day 12 post IUI. Then as follows:8.8 when tested 14 days post IUI, 22 when tested 16 days post, 71.8 when tested 18 days post and 160 when tested 20 days post. I know that the levels are doubling every 48 hours or so but they still look low when I look at averages and ranges. I have had 2 losses with the past 8 months. What are the chances that this pregnancy will be successful? Thank you