Trying to Conceive

Understanding Your Basal Body Temperature (BBT)

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When you’re trying to get pregnant, the more tools and information you have, the better equipped you’ll be to make a conception plan. One of the most helpful indicators to be aware of and to chart over the course of a few months is called Basal Body Temperature (BBT).

Why Should I Track My BBT?

Taken first thing in the morning, even before sitting up in bed, your basal body temperature (BBT) is the lowest temperature your body reaches during rest. During the first half of your menstrual cycle — the follicular phase — your basal body temperature will be lower. At this time, your ovaries are preparing for ovulation by developing egg containing follicles within the ovary. Right before the egg is released from the ovary (also called ovulation), some women experience a very slight drop in temperature. If this is the case for you, you’re going to want to have intercourse as soon as you notice this drop.

Immediately after the egg has been released from the ovary, there will be a sharp rise in temperature. This signals that you are entering the luteal phase of your cycle, or the time after ovulation has occurred. By the time you notice this temperature increase, you have already ovulated.

This is why it’s important to chart your BBT for several months, so you can notice trends and get to know how your body works, so you know when to time intercourse for the best chance at conceiving. Or, conversely, when to use a secondary form of birth control — such as a condom — to prevent pregnancy from happening.

How Will I Know if My BBT Has Risen?

What you are looking for is a temperature rise of 0.4 degrees Fahrenheit or more. If ovulation has occurred, your temperature will remain higher. If your temperature remains high for more than three days, you can assume you have ovulated.

What If I Don’t See My BBT Increase?

Some women don’t experience a temperature shift. If you don’t see a temperature shift after a couple of months of charting, talk with your doctor. He or she will most likely run some blood tests during your cycle to determine whether or not you are ovulating.

What If I Still Don’t Get Pregnant?

Any single BBT chart will probably not get you pregnant. The benefit of BBT charting is looking at trends over the course of several months, so you can better understand your menstrual cycle and pinpoint when you ovulate each month.

As a result, if you have irregular menstrual cycles that vary in length month-to-month, BBT charting will not be as effective. Women with irregular cycles should always consult with a health care provider to figure out why their cycles are irregular.

If you have charted your BBT for several cycles and have not achieved pregnancy or are concerned, talk with your doctor. Bring your BBT charts with you, as they will be helpful in showing ovulation trends and determining if there are any problems.

Dr. Alan Copperman is a board-certified reproductive endocrinologist and infertility specialist with a long history of success in treating infertility and applying fertility preservation technologies. He serves as Medical Director of Progyny, a leading fertility benefits management company, and co-founded and serves as Medical Director of RMA of New York, one of the largest and most prestigious IVF centers in the country.  Dr. Copperman is also the Vice Chairman and Director of Infertility for the Icahn School of Medicine at Mount Sinai, and Chief Medical Officer of Sema4, a health information company. Dr. Copperman has been named to New York magazine’s list of Best Doctors 17 years in a row. He has been recognized by his peers and patient advocacy organizations for his commitment to patient-focused and data-driven care. He has published more than 100 original manuscripts and book chapters on reproductive medicine and has co-authored over 300 scientific abstracts on infertility, in vitro fertilization, egg freezing, ovum donation, and reproductive genetics. 

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