10 weeks earlier: If you were 12 weeks pregnant on 7/18, you conceived 10 weeks earlier or about 5/9. Even with irregular periods most women ovulate some so pregnancy is always possible. By convention we count weeks of pregnancy from last menstrual period which is about 2 weeks before conception. This doesn't necessarily work with irregular periods but the ultrasound doesn't go by periods. It measures fetal size.
Answered 8/13/2014
3.8k views
From US...: Given gestational age of 12 weeks on July 18th, sex for conception likely occurred 5/5-5/10. Given your irregular cycles the LMP isn't reliable to use. Good luck.
Answered 8/12/2014
3.8k views
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