The chart below shows the blood levels of ethinyl estradiol and etonogestrel achieved with NuvaRing^®. The percentage of estrogen absorbed into the bloodstream (i.e. bioavailability) is the same whether given orally or through the vagina. The blood levels of ethinyl estradiol achieved with NuvaRing^® are about half of that seen with a 30 microgram oral contraceptive pill and truly reflect NuvaRing^®'s 15 microgram delivery of estrogen.

Note that fairly even blood levels occur throughout most of the cycle, which is what most likely accounts for the very low breakthrough bleeding rates of NuvaRing^®.