TSH and Prolactin: Two Fertility Hormones You Might Be Missing

When thinking about your fertility and the many, many parts that play a role in it, sometimes we overlook certain aspects of our body...
Kristyn Hodgdon •Aug 15, 2022

When thinking about your fertility and the many, many parts that play a role in it, sometimes we overlook certain aspects of our body that might have a larger influence than we know. Many at-home fertility hormone test kits check your body’s anti-mullerian hormone (AMH), follicle-stimulating hormone (FSH), and luteinizing hormone (LH).

While these are often key players and should 100% be tested, there are other hormones that we should be considering, as well: thyroid-stimulating hormone (TSH) and prolactin. While most at-home fertility tests on the market don’t include TSH or prolactin, twoplus Fertility’s comprehensive Hormone Test Kit tests for both while also being affordable if you’re on a budget. 

So, why are these seemingly-unrelated hormones produced in the brain’s pituitary gland important to fertility? Let’s break it down and look at the many ways too much or too little of these two hormones can negatively impact your chances at conception. 

TSH Levels and Fertility

As you might know, your thyroid health and fertility are linked. If you suffer from unaddressed hypothyroidism or hyperthyroidism, it can have negative effects on your fertility. Your thyroid is a small gland located in your neck, just above your collarbone, and it plays a pivotal role in the body’s endocrine system. 

When your thyroid is not functioning correctly, it can greatly impact your overall health. How? Well, the pituitary gland in the brain sends out a hormone called thyroid-stimulating hormone (TSH) to the thyroid gland. TSH tells the thyroid gland how much triiodothyronine (T3) and thyroxine (T4) to produce and secrete. When properly functioning, your thyroid will produce the right amount of hormones to keep your body’s metabolism running and balanced, which transforms the food you eat into the energy you need.

If you have abnormal TSH levels—either too low or too high—it can result in hypothyroidism or hyperthyroidism. Both conditions affect fertility by disrupting menstrual cycles and can even increase the risk of miscarriage or premature birth.

The normal TSH levels should fall between 0.5 to 5.0 mIU/L. Testing your TSH levels while trying to conceive is a great place to determine if you suffer from underlying conditions that might be challenging your attempts to get pregnant. 

Prolactin Levels and Fertility

Also produced in the pituitary gland, which we know sends TSH to the thyroid, prolactin is a hormone that tells the body to produce breast milk when pregnant or breastfeeding. During pregnancy, prolactin levels naturally rise and remain elevated in people who are breastfeeding. Non-lactating people’s prolactin levels typically go down 2-3 postpartum or about 6 months postpartum for those lactating. 

The typical amount of prolactin in a woman’s bloodstream should be less than 25 ng/ml. Similar, again, to TSH, too little or too much of prolactin can negatively affect fertility. Too much prolactin, or hyperprolactinemia, is more common than too little prolactin, or hyperprolactinemia. Elevated prolactin can cause irregular periods, infertility, breast tenderness, and premature menopause. 

Not only that, thyroid health and prolactin levels can actually be linked: hypothyroidism (underactive thyroid, in which the thyroid gland does not produce enough thyroid hormone) is known to cause higher prolactin levels, which is why testing for both is crucial to getting the whole picture. 

While the body’s natural prolactin levels rise and fall throughout the day, testing is recommended about three hours after waking up to get the most accurate reading. 

Testing For Fertility At Home

twoplus Fertility’s new Hormone Test Kit is one of the only at-home fertility tests on the market that tests for both prolactin and TSH. Unlike a traditional blood test conducted at a clinic or physician’s office which takes two vials of blood, this one only requires 8 drops of blood and a small finger prick. All blood samples mailed back to twoplus Fertility are then processed in reputable CAP- and CLIA-accredited facilities that work with the top fertility clinics in the U.S. To learn more, click here and use the code FR15OFF for 15% off your purchase. 


Brighid Flynn is a freelance writer based in Philadelphia where she lives with her husband and puppy. She is just beginning her journey toward motherhood.