Possible Pregnancy: Calculating Conception Timeline & Ovulation

Question
I am 44.my wife is 31. I have one son.My wife who is abroad told me she is one mth. pregnant. Her last period is on 8.12.2005. We only had sex on the 30.12.05 and 05.01.06. I am confused. Could she be one mth.given the circumstances above? Cos most of her times she is away. Please advise. Thank you.

Answer
If your wife has a normal 28 day cycle (from the first day of her period until the first day of her next period) ovulation occurs on cycle day #14, and she can only conceive if she has sex on cycle day #13, 14, 15, or 16. If her last period started on December 12, she would have ovulated on December 25 and could only have conceived if she had sex on December 24,25,26, or 27.  That would make her 7 weeks 3 days (from her last period), not one month. If she has a cycle that is longer or shorter than 28 weeks, she may have ovulated earlier or later than cycle day #14.  Later on in the pregnancy, a sonogram can be done and can pinpoint the exact date of conception. There is no way to determine if she is only one month (4 weeks) pregnant because a sonogram will not see anything untiil 5.5 weeks. A pregnancy test can become positive in one month but that will not determine the date of conception.