TSH and Prolactin: Two Fertility Hormones You Might Be Missing

When you’re trying to figure out why getting pregnant feels harder than it should, most people start with the usual suspects: FSH, LH, estradiol, AMH, and progesterone. Some of these are especially helpful in the luteal phase, like progesterone, FSH, estradiol, and AMH, while LH is more useful earlier in the cycle. But two hormones often fly under the radar even though they can seriously influence ovulation, cycle regularity, and your chances of conceiving: TSH and prolactin.

Both of these hormones are made in the pituitary gland, and while they don’t get as much attention as ovarian reserve or ovulation tracking, they play a surprisingly big role in cycle regularity, ovulation, and early pregnancy. They’re also deeply interconnected, which is why many clinicians test them together when someone’s dealing with irregular cycles, unexplained infertility, or recurrent loss.

So if you’ve been testing all the “right” fertility hormones and still feel like something’s missing, this is where TSH and prolactin come in.

TSH and prolactin: why these two hormones matter together

TSH and prolactin are both produced in the pituitary gland, the command center for your reproductive hormones. That shared origin matters. When one side of the system is off, the other can easily get pulled out of balance.

Clinicians often test TSH and prolactin at the same time because:

• They’re both influenced by the hypothalamus
• They can rise together when thyroid function is low
• They each have direct effects on ovulation, menstrual cycles, and implantation
• They’re common but overlooked causes of irregular periods or anovulation

And in the bigger fertility picture? Your ovarian reserve and ovulation hormones only tell part of the story. Thyroid function and prolactin levels often explain the symptoms that initial fertility tests might miss.

TSH levels and fertility

Your thyroid is a small gland in your neck, but it punches way above its weight when it comes to fertility. Thyroid health affects metabolism, energy production, menstrual patterns, luteal phase length, and even early embryo development.

TSH, or thyroid-stimulating hormone, is the pituitary hormone that tells your thyroid how much T3 and T4 to produce. When TSH is off, this can indicate:

• Hypothyroidism (TSH high)
• Hyperthyroidism (TSH low)

Both can disrupt ovulation, lengthen or shorten your cycles, and increase the risk of miscarriage, according to guidance from the American Thyroid Association (2023).

Symptoms of thyroid dysfunction that can affect fertility include fatigue, weight changes, hair thinning, constipation, feeling unusually cold or hot, heavier or lighter periods, and difficulty regulating mood. Many people brush these off as “just stress,” but they’re worth paying attention to.

And when it comes to early pregnancy?

Abnormal TSH levels can interfere with implantation and early embryo development. This is why many clinicians aim for an “optimal” TSH range (often 0.5 to 2.5 mIU/L) in the months leading up to conception and during the first trimester, according to various studies, including this 2016 review.

Prolactin levels and fertility

Prolactin is best known for helping produce breast milk during pregnancy and postpartum, but it has another job most people don’t realize: it helps regulate ovulation.

When prolactin is too high (a condition called hyperprolactinemia), it can block GnRH (gonadotropin-releasing hormone), which then suppresses FSH and LH. The result? Irregular or missing periods, anovulation, or long cycles that feel unpredictable.

Symptoms of elevated prolactin can include irregular periods, breast tenderness, low libido, headaches, unexpected milk production, vaginal dryness, or difficulty ovulating. Some people also experience sleep issues, mood changes, or temperature dysregulation.

High prolactin is treatable, but it often goes undiagnosed simply because it isn’t typically included in initial fertility testing, although further testing is tailored to individual symptoms and risk factors.

The TSH and prolactin relationship: How they affect each other

Here’s the part that most people don’t know: TSH and prolactin aren’t just neighbors in the pituitary. They’re linked by the same upstream hormone.

The hypothalamus produces TRH (thyrotropin-releasing hormone).

TRH stimulates the pituitary to release TSH, but it also stimulates prolactin.

So when your thyroid is underactive, your TRH levels increase in an attempt to push the thyroid to work harder, as shown in this 2011 study for the Caspian Journal of Internal Medicine. And because TRH stimulates both hormones, prolactin often rises too.

This is why someone can have high TSH and high prolactin at the same time.

Can high TSH cause high prolactin?

Yes. The mechanism looks like this:

1. Thyroid is underactive
2. Hypothalamus releases more TRH
3. TRH increases TSH production
4. TRH also increases prolactin production
5. Both levels can be elevated on your labs

What counts as high?

• TSH: Labs may flag levels above 4.0–5.0 mIU/L as high, but fertility specialists often aim for 0.5–2.5, so your provider may target that range even if your TSH is technically normal.
• Prolactin: Above 25 ng/mL for non-pregnant adults

This is one reason clinicians often correct thyroid issues before jumping to prolactin medications.

Normal TSH and prolactin levels

When you’re trying to understand whether your hormones are helping or hindering conception, it really helps to have the actual numbers in front of you. For TSH, the general reference range is 0.5 to 5.0 mIU/L, although many clinicians consider 0.5 to 2.5 mIU/L to be the optimal window when you’re trying to conceive or in early pregnancy. Prolactin has its own benchmark, with most non-pregnant, non-lactating adults falling below 25 ng/mL.

If you’re wondering why you’ll sometimes see different ranges online or from different clinicians, it’s because “normal” varies slightly by lab, testing method, and even by where you are in your cycle. What’s considered acceptable for everyday health isn’t always the same as what’s ideal for conception, which is why clinicians interpret these numbers in context rather than isolation.

Timing your tests also makes a difference. TSH can be checked at any time, though morning draws are most common because it follows a daily rhythm. Prolactin is best tested about three hours after waking, and it’s important to avoid intercourse, nipple or breast stimulation, and exercise beforehand since all three can temporarily raise levels. These small details can shift your results just enough to matter when you're trying to understand irregular cycles or inconsistent ovulation.

High TSH and prolactin levels: What they mean for fertility

When both hormones are off, it creates a double barrier to conception.

High TSH can cause:

• Irregular cycles
• Difficulty ovulating
• Luteal phase defects
• Increased miscarriage risk

High prolactin can cause:

• Suppressed ovulation
• Long or absent cycles
• Low progesterone
• Infertility due to ovulatory dysfunction

On their own or together, they can significantly reduce your chances of conceiving, even if your ovarian reserve looks great on paper. That’s why many clinicians start with thyroid treatment first. As Dr. Caledonia Buckheit, OB/GYN, explains, “Fixing TSH can normalize prolactin in some cases, other times, however, the prolactin elevation is caused by something else, that requires its own management.”

Elevated prolactin and TSH: Common causes

There are several reasons these two hormones can rise together:

• Primary hypothyroidism: The most common cause.
• Pituitary tumors (prolactinomas): Usually benign but can elevate prolactin and disrupt TSH signaling.
• Medications: Antidepressants, antipsychotics, opioids, blood pressure meds.
• PCOS: A subset of people with PCOS have mildly elevated prolactin.
• Stress and sleep disruption: Both can raise prolactin temporarily.

If your results look off, it doesn’t automatically mean something serious is happening. But it does mean further testing is helpful.

What to do if your TSH and prolactin are abnormal

First, take a breath. Both thyroid issues and hyperprolactinemia are treatable, and most people see improvements quickly once treatment starts.

Common next steps include:

• A full thyroid panel (TSH, free T4, free T3, antibodies)
• Repeat prolactin testing if the first result was borderline
• An MRI if prolactin is very elevated (above 100 ng/mL)
• Reviewing medications and supplements
• Discussing treatment options

How soon can you try to conceive again?

Often immediately after levels start moving into the optimal range. Many people see cycles regulate within 1 to 3 months.

Success rates are encouraging. Once thyroid and prolactin levels normalize, ovulation typically returns and pregnancy chances rise accordingly.

Testing at home: TSH and prolactin

Traditional testing is almost always done through your doctor, and you should follow their guidance on when to repeat labs or monitor levels over time. Most clinicians rely on standard laboratory testing for thyroid and prolactin checks, so unless your provider tells you otherwise, that’s typically the safest and most accurate way to track changes.

There are a few things to remember, though. Prolactin is most accurate when tested about 3 hours after waking, while TSH is typically retested 6 to 8 weeks after starting thyroid medication. And while at-home kits might seem convenient, they don't replace proper clinical testing, especially if your levels are abnormal or prolactin is elevated. In many cases they add little to your actual care plan, so it’s worth saving your money and sticking with the lab work your doctor recommends.

If one hormone comes back in range and the other doesn’t, don’t brush it off. Because TSH and prolactin often influence each other, treating one can bring the other into a normal range, and understanding both gives you a clearer picture of what’s going on with your fertility.

Questions to ask your doctor about TSH and prolactin

Talking to your doctor about hormone testing can feel intimidating, especially when you’re already juggling symptoms, uncertainty, and the emotional weight of trying to conceive. But asking the right questions can make all the difference. TSH and prolactin aren’t always part of the initial fertility workup, so opening the door to a deeper conversation helps ensure nothing important gets overlooked. You deserve clear answers, and advocating for yourself is a powerful step toward understanding what your body needs.

• Should I test both, or start with one based on my symptoms?
• What’s the optimal range for conception, not just the normal lab range?
• Do I need additional thyroid tests, like T3, T4, or thyroid antibodies?
• Could any of my medications be affecting my prolactin or TSH levels?
• How often should I retest while trying to conceive?
• If both hormones are high, which one should we treat first?

Where TSH and prolactin fit into your next steps

Understanding TSH and prolactin can be a game changer when you feel like you’ve tested everything and still aren’t getting answers. These two hormones might not be the first ones people think of when they start exploring fertility, but they often explain symptoms and cycle patterns. And the good news is that when something is off, both thyroid concerns and high prolactin are usually treatable, often with strong improvements in cycle regularity and ovulation once levels settle into the optimal range.

If your labs come back abnormal, it doesn’t mean you’ve missed your chance. It simply means your body is asking for support. With the right testing, treatment, and follow up, many people see things improve quickly, which can be incredibly reassuring when the TTC process already feels heavy. Knowledge really is power here. The more you understand how TSH and prolactin shape your fertility, the more confident you can feel advocating for the care you deserve and moving forward with a clearer plan. You’re not behind, you’re not missing something obvious, and you’re absolutely allowed to ask for a deeper look.