For as long as I've been doing this study, I've been finding similar numbers of boy and girl charts with one-time BD. Usually there are slightly more boy charts, but after looking at these last 200 charts, I now have slightly more girl charts. 35 girl charts had one-time BD, and 33 boy charts had one-time BD, which results in a 51.5% preference for girls (35/68 charts).
However, what was significant was the day the one-time BD occurred on.
- 1 day after ovulation: 0 boy charts, 1 girl charts (sways girl 100%)
- on the day of ovulation: 7 boy charts, 6 girl charts (sways boy 53.8%)
- 1 day before ovulation: 15 boy charts, 8 girl charts (sways boys 65.2%)
- 2 days before ovulation: 2 boy charts, 7 girl charts (sways girl 77.8%)
- 3 days before ovulation: 2 boy charts, 5 girl charts (sways girl 71.4%)
- 4 days before ovulation: 2 boy charts, 6 girl charts (sways girl 75%)
- 5 days before ovulation: 3 boy charts, 1 girl chart (sways boy 75%)
- 6 days before ovulation: 2 boy charts, 0 girl charts (sways boy 100%)
- 7 days before ovulation: 0 boy charts, 1 girl chart (sways girl 100%)
Again, a lot of these statistics are questionable because there aren't many charts with one-time BD. However, there is a general trend where BD the day of ovulation or 1 day prior favors boys (22/36, sways boy 61.1%), BD 2-4 days prior to ovulation favors girls (18/24, sways girl 75%), and BD 5+ days prior to ovulation favors boys (5/7, sways boy 71.4%). One-time BD does seem to sway - but how it sways depends on what day the BD occurred on.
One-time BD is also not the best way to get pregnant. Out of 700 charts only 68 (9.7% of the charts) had just a single time of BD.