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The Center for Fertility and Gynecology

Ask Dr. Marc.........Basal Body Temperature

By Paula Hovell on May 15, 2013

This question and answer was originally published on the blog  by Katie: "Infertility Warrior, Mommy to two, wife of rock and roller, Child and Adolescent Psychotherapist , and Parenting Expert in Los Angeles, CA"  

Dear Dr. Marc,

My main question/concern is about the trigger shot. I do BBT charting every morning. Does the HCG shot effect one's temps? I had my IUI last Saturday- trigger shot Thursday night. Thursday am my temp was at its lowest- after entering Sundays in the chart, it read that I ovulated Thursday. So I'm worried the IUI was done too late.

Thank you!


Hi Temperature Checker,

To answer this question completely, I need to give you some background information on eggs, ovulation and the hormonal activities surrounding this amazing event!

Women are born with all of the eggs they will ever have.  Those eggs exist within the ovaries in small sacks of fluid called follicles.  Beginning with the first few days of a menstrual cycle, one of the many follicles present in one of the ovaries is selected as the “dominant’ follicle.   Under stimulation form the brain, that follicle will begin to grow faster than the other follicles.  This process continues for about 14 days when the dominant follicle reaches roughly 2 cm in diameter.  At this point, the brain sends a hormone single to the ovary which instructs the follicle to release its egg.  This is called ovulation, and the signal sent from the brain is a hormone called LH (luteinizing hormone).  Once the egg is released, it hopefully finds its way into the fallopian tube where, with a little luck, it can meet a nice spermatozoon and transform into an embryo!

Basal body temperature is related to all of this because once the follicle releases the egg, its job is not over.  The follicle transforms in to a structure called the corpus luteum.  The corpus luteum produces progesterone, which is critical to maintain a pregnancy and has many effects throughout the body.  Once of these effects is to raise the basal temperature by about half of a degree (0.5°C).  In reference to ovulation, if we can detect this rise in temperature, then we can assume that ovulation has occurred within about 48 hours.   

In your situation, you took an HCG shot.  HCG is structurally very similar to LH, but it lasts considerably longer in the body.  Doctors use HCG to induce ovulation in the same way that the brain induces ovulation with LH.  Ovulation almost always follows HCG injection by about 36-40 hours.  With this in mind, your IUI was perfectly timed.   

Based on your BBT, a rise on Sunday can be consistent with ovulation on Saturday.  The only caveat is if your natural LH surge occurred prior to the time you took the HCG shot.  If you were monitored with ultrasound, this is pretty unlikely because your doctor would be able to see the dominant follicle. 

If you were not monitored by ultrasound, there is a possibility that you ovulated early.  My recommendation is if you do not become pregnant this month, consider close monitoring with ultrasound next month.

I hope this is helpful, good luck.  If you have any other questions, feel free to contact me here


Dr. Marc


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