Spotting before your period is one of the most common times that women notice bleeding outside of their normal menstrual cycle. There are many different reasons why you might experience spotting, but when it happens in the week before your period is due (during what is called the luteal phase) it is usually related to fluctuations in hormone levels.
Spotting before your period can be a normal part of a healthy menstrual cycle. For some women, this type of spotting occurs consistently in every cycle. For other women, premenstrual spotting may occur only sporadically. Occasionally, spotting before your period is due can be a sign of low progesterone levels.
What causes spotting before your period?
In order to understand what causes spotting before your period, it’s important to know what is happening hormonally at that point in your cycle. During your period, your body is shedding the uterine lining. Right after your period ends, it’s time to build that uterine lining back up. The hormone estrogen, which increases starting after your period, is responsible for growing the uterine lining.
Around the mid-point of the menstrual cycle, ovulation occurs. An egg bursts out of a follicle in one of the ovaries, and the spent follicle transforms into a corpus luteum, which secretes progesterone. Ovulation marks a dramatic turning point in hormone levels: estrogen drops, and progesterone increases.
One of progesterone’s jobs is to provide structural support to the uterine lining. As long as the corpus luteum keeps secreting enough progesterone, the uterine lining stays attached to the uterus. After about 10 – 16 days, the corpus luteum runs out of progesterone, and the sudden drop in hormone levels causes your period to start (if you are pregnant, the corpus luteum keeps on producing progesterone, and you do not get your period).
For the same reason that a big drop in progesterone causes your period to start, a small drop in progesterone can cause spotting. Now, you’re probably wondering—why would progesterone levels drop several days or even a week before your period is due?
Why causes progesterone to drop?
The corpus luteum produces moderate amounts of estrogen as well as progesterone, and this estrogen can transiently reduce progesterone production. When this secondary estrogen surge occurs happens, you may also notice a slight temperature dip and fertile cervical mucus, even though you’ve already ovulated. The relative reduction in progesterone may cause light spotting.
Spotting during the luteal phase can also be a sign that your progesterone levels are too low. Progesterone is an important hormone for achieving pregnancy, because it helps ensure that the uterine lining is thick and mature enough for an embryo to implant. When progesterone levels are too low, you may experience luteal phase spotting or a short (less than 10 day) luteal phase.
If you’re worried that you may have low progesterone, talk to your doctor about it. Spotting before your period isn’t enough to conclusively diagnose anything, but if it happens consistently, it’s worth looking into. Make sure that your doctor tests your progesterone at the right time in your cycle. Progesterone is usually tested on cycle day 21, which is when progesterone levels would be highest in a 28-day cycle with ovulation on day 14. But if you ovulate significantly earlier or later than day 14, you shouldn’t test progesterone on day 21, but instead test seven days after ovulation.
Does spotting before your period mean you could be pregnant?
Spotting in the luteal phase is not an early sign of pregnancy, unfortunately. It’s just a consequence of changing hormone levels in the cycle. There’s a lot of talk in online forums about implantation bleeding, which supposedly occurs as the embryo is attaching to the uterine wall. But luteal phase spotting doesn’t have anything to do with implantation, and should not be considered an implantation symptom. Actually, cycles that end in pregnancy are less likely to have bleeding in the luteal phase than cycles that don’t1.