Need some Advice

I have a site that as been on google for the last 2 years, and it has gone up and down the rankings a number of times, but i have never been able to maintain a stable position. For the last 2-3 months it has shifted between No 11 and number 20, i think at the moment it is sitting no. 18 for my main search term.

The site in question is http://www.pregnancy-info.net and the main keyword is "pregnancy". Although the site is highly ranked for other search terms such as pregnancy stages, pregnancy symptoms etc. I would really like to get the pregnancy search term under the belt aswell.

I would really appreciate it if you guys could have a look at the site, and let me know where I am going right and wrong.

regards and thanx in advance for any help

The one thing i noticed about the top 3 when searching for the term pregnancy, is that all of them start their meta descriptions with the first word being Pregnancy. Your description has the word Pregnancy as the fifth word. Just a thought...