LH Surge Before Period? What Causes a Positive OPK Before AF

While its arguably a waste of tests, many women continue to use LH test strips (OPKs or ovulation prediction kits) after ovulation. Many of those same women then find themselves with a positive test just before their period or aunt flow (AF) in TTC-speak. Some assume this means they are pregnant, as LH strips can pick up hCG, the hormone detected by pregnancy tests. Others are confused and wondering if they are experiencing double ovulation or failed to ovulate earlier in their cycle. Either way, the situation leads many to ask the Google gods, “LH surge before period” or “LH surge before AF.” So, which is it? Pregnancy or ovulation? Neither.

OPK positive before period LH surge before AF

What is LH and what does it do?

LH is an abbreviation for luteinizing hormone. Produced by the pituitary gland, it works to mature follicles for ovulation, and then subsequently triggers ovulation via a “surge.” This is why LH test strips can be used to reliably predict ovulation within 24 to 36 hours.

Low levels of LH also help to maintain the corpus luteum, a structure formed in your follicle after ovulation. The corpus luteum secretes the hormone progesterone to maintain your uterine lining for pregnancy. It’s progesterone that produces the temperature shift those who basal body temp can detect to confirm ovulation.

LH is always present in your cycle. As a result, LH test strips will almost always show two lines, and are only positive if the test line is as dark or darker than the control line.

Why can LH surge before a period?

Progesterone also suppresses LH to prevent ovulation while the body is waiting, so to speak, to see if it becomes pregnant. As a drop in progesterone is what triggers your period to begin, often when progesterone drops LH briefly sees an upturn as well. Depending on your personal hormone balance that uptick may be significant enough to show a positive OPK or at the least a darker line than was seen in the pattern on previous days.  It should also be kept in mind that your hormone levels do fluctuate from cycle to cycle. This means seeing an LH surge before your period when you haven’t previously isn’t a sign you’re pregnant.

LH surge before AF Positive OPK before period


 Can you have an LH surge before your period and still be pregnant?

Following that logic you might think that an LH surge being a sign your progesterone has dropped, indicates your period is incoming, and the month is a wash conception wise. In most cases that, unfortunately, is likely true, but it is possible to get an LH surge before your period and still be pregnant.

Sometimes when implantation occurs late in your cycle, progesterone levels can begin to fall and then rebound, in this instance spotting or light bleeding may also occur. In other cases, implantation itself causes a slight hormone dip (visible by a temperature dip as well) which would likewise allow for a slight LH rise.

Finally, while an OPK can react to hCG, it takes a higher level of hCG to produce a positive result. This means that a pregnancy test would show positive long before an OPK. It’s a myth that an OPK can be used as an early result pregnancy test before an actual pregnancy test.

We hope this has cleared up some of your questions, but if you have more, feel free to drop us a comment.

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