What if day 21 of my menstrual cycle falls on a weekend?

If you have ordered a day 21 progesterone test to check whether or not you have ovulated you can take your sample over the weekend. This is because progesterone is stable at room temperature for 72 hours, so you can collect your sample on Saturday or Sunday and post it on Monday to reach the laboratory on Tuesday. 

We generally advise customers not to collect and post samples over the weekend because some biomarkers degrade or spoil in a day or two. This is not the case with progesterone. We advise you to store your sample in a cool dark place at home before posting it on a Monday, rather than putting it in the postbox straight away.