Yes, some women release an egg from each ovary each cycle. It usually runs in families, hence the very high rate of fraternal twins within mine where both sisters have had them, but they actually haven't been conceived on the same day but one week apart. So far, I've just been lucky enough to become pregnant on the first month of trying both times by DTD every second day, but next time I'm hoping for the double whammy. For my mother, no.1 sister and me, this quirk has been a blessing so far, however for sister no.2 it's been both a blessing and a curse as she has m/c many babies within a short timeframe. She has three beautiful girls now, but for some reason just can't hold onto the boys, and this seems to be another family quirk. My DS and my brother are the only non-twin boys within a couple of generations, any other boys have seemed to need to piggy back with a sister to make it through to the end.

Women also release more eggs the older they get, hence the reason for higher incidences of twins within women over 35.