Month of Conception
  Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
  18 F M F M M M M M M M M M 17% 83%
  19 M F M F F M M F M M F F 50% 50%
  20 F M F M M M M M M F M M 25% 75%
  21 M F F F F F F F F F F F 92% 8%
  22 F M M F M F F M F F F F 67% 33%
A 23 M M M F M M F F F M M F 42% 58%
g 24 M F F M M F M F M M F M 42% 58%
e 25 F M F M F M F M F M M M 42% 58%
  26 M M M M M F M F F M F F 42% 58%
a 27 F F M M F M F F M F M M 50% 50%
t 28 M M M F F M F M F F M F 50% 50%
  29 F M F F M F F M F M F F 67% 33%
C 30 M M F M F M M M M M M M 17% 83%
o 31 M M M M F F M F M F F F 50% 50%
n 32 M F F M F M M F M M F M 42% 58%
c 33 F M M F F M F M F M M F 50% 50%
e 34 M M F F M F M M F M F F 50% 50%
p 35 M F M F M F M F M M F M 42% 58%
t 36 M F M M M F M M F F F F 50% 50%
i 37 F F M F F F M F F M M M 58% 42%
o 38 M M F F M F F M F F M F 58% 42%
n 39 F F M F F F M F M M F M 58% 42%
  40 M M M F M F M F M F F M 42% 58%
  41 F F M F M M F F M F M F 58% 42%
  42 M F F M M M M M F M F M 33% 67%
  43 F M F F M M M F F F M M 50% 50%
  44 M F F F M F M M F M F M 50% 50%
  45 F M F M F F M F M F M F 58% 42%
Female 43% 43% 50% 57% 43% 54% 36% 54% 54% 43% 54% 50% 48%
Male 57% 57% 50% 43% 57% 46% 64% 46% 46% 57% 46% 50% 52%
This chart is believed to have been buried in a tomb near Beijing for almost 700 years and the original is now in the Beijing Institute of Science. By cross-referencing the month a child was conceived with the age of the mother at conception, the sex of the child may be determined. This chart has been proven to be 93% accurate.
According to this ancient data, your best chances for a boy occur when the mother conceives in July when she is 18, 20, 30, and 42. The best chances for a girl occur when the mother conceives in April when she is 21, 22, and 29. Also according to the study a boy is 54% more likely to be born. Have Fun!
Shelly Wu
 
The information in this page was copied from: http://www.chineseastrology.com/wu/birthchart.html