Why do doctors always ask about your last menstrual period? Experts explain.

An unwrapped tampon in a woman’s hand.
Your period can reveal a lot about your health. (Getty Images)

No matter what brings a woman to the doctor’s office, she can expect one question without fail: “When was the first day of your last menstrual period?”

Dr. Alla Vash-Margita, chief of pediatric and adolescent gynecology at Yale Medicine, tells Yahoo Life that although one reason for the question is to gauge whether a woman might be pregnant, the answer can reveal much more about a woman’s health.

“Gynecologists pay close attention to menses in general,” she explains. “In fact, menses has been proposed to be considered as a vital sign in people with a uterus. Regular periods ... are just as important as blood pressure, respiratory rate, temperature, heart rate.”

Because periods can reveal so much about a woman’s health, says Vash-Margita, all doctors — not just gynecologists — should pay attention to women’s periods.

Vash-Margita says that regular periods are “a sign of a healthy body.” She explains that periods that stop or are spaced out more than 45 days apart may be a symptom of “thyroid gland disease, disordered eating, strenuous exercise, polycystic ovary syndrome (PCOS) and a few other conditions” apart from pregnancy.

In addition to tracking the day that periods start, Dr. Myda Luu, area specialty chief of ob-gyn for Kaiser Permanente, recommends that people who menstruate track “cycle duration, frequency and flow,” as well as “associated symptoms such as severe cramping, pain with intercourse, bleeding between periods, changes in mood during the menstrual cycle and migraines.” That’s because these symptoms can be useful in the diagnosis and treatment of several different health conditions.

Without tracking, women may miss changes that are important to their overall health, especially if those changes are subtle or happen gradually.

Even if a woman doesn’t have immediate health concerns and isn’t worried about getting pregnant, monitoring periods can help establish a baseline that may be useful later. Symptoms that indicate a problem for one woman may be completely normal for another, depending on her health history.

Luu explains that “knowing the first day of your last menstrual period is generally about tracking your menstrual cycles and understanding what is normal for you.” She adds that tracking periods and associated symptoms can show “important changes that may warrant further investigation.”

She advises anyone who menstruates to tell their doctor if their cycles are longer than 35 days or shorter than 21 days, they bleed for more than seven days, they soak through one or more tampons or pads in less than two hours, they don’t have a period for more than three months, they experience severe pain at any point during their cycle or they bleed between periods, after intercourse or after menopause.

If a woman notices changes in her cycle, however, experts say there is no need to panic. Dr. Dan Nayot, an ob-gyn, reproductive endocrinologist and infertility specialist and chief medical adviser for Bird&Be, tells Yahoo Life: “There are lots of options to medically manage menstrual cycles to improve ... quality of life.” Nayot advises that those who menstruate advocate for themselves “if the frequency, duration, amount of flow or associated pain are having a negative impact” on their lives. He adds that anyone who menstruates should “be proactive” with their care and see their doctor for blood work and other testing if they have any concerns.

Knowing the first day of a woman’s last menstrual period is useful in other ways. Dr. Arlene Go, an ob-gyn and specialist fellow studying endometriosis at Hera Biotech, tells Yahoo Life that it’s important to know “what phase in the cycle is the patient at that time, follicular or luteal. Sometimes symptoms are tied to a certain part of their cycle, and this is important to know for both diagnosis and treatment.” Without knowing the date of a patient’s last menstrual period, it can be hard to determine where they are in their cycle.

Liesel Teen, a labor and delivery nurse and founder of Mommy Labor Nurse, explains thatwhere you are in your menstrual cycle can affect different things, including your weight, vaginal discharge, breast texture and vital signs,” so knowing the first day of your last menstrual period is “important information” for your provider. Teen tells Yahoo Life: “If your provider notices a change in your health from your last visit, it’s helpful to know whether that change could be caused by where you are in your cycle” or something more serious.

For example, screening for breast cancer can be impacted by where a woman is in her menstrual cycle. “Your breasts may feel more lumpy at certain points of your cycle compared to others,” Teen explains. “Knowing this information could help your provider determine if the texture change is related to your cycle or if it should be investigated further.”

Teen recognizes that it can be hard to remember all this information. So she recommends that anyone who menstruates track their periods and symptoms with an app, a calendar or a journal. Nayot adds that “aggregated data” over time gives doctors even more insights about a patient’s menstrual cycle. “Looking back at your cycles and associated symptoms might uncover some interesting patterns that might be beneficial to the patient,” he says.

Teen agrees, saying: “There’s a lot of insight that can be gained from your menstrual cycle, so having accurate information to give your provider is extremely helpful.” Although women may be embarrassed to talk about their period, Teen says doing so is “no different than discussing your blood pressure results or any other health concerns,” adding that it’s “important to discuss.”

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