TSH and the thy­roid when try­ing to con­ceive: Which val­ues mat­ter?

How does the TSH lev­el affect fer­til­i­ty?

The thy­roid pro­duces hor­mones that influ­ence numer­ous meta­bol­ic process­es in the body and also play a role in the female cycle and repro­duc­tion. Pro­nounced thy­roid dys­func­tion can there­fore also be rel­e­vant when try­ing to con­ceive.

The most impor­tant lab­o­ra­to­ry val­ue for an ini­tial assess­ment of thy­roid func­tion is TSH (thy­roid-stim­u­lat­ing hor­mone). If the val­ue is abnor­mal, fur­ther tests such as mea­sur­ing the free thy­roid hor­mone fT4 and—depending on the clin­i­cal question—thyroid anti­bod­ies may be use­ful.

Whether a thy­roid eval­u­a­tion is nec­es­sary when try­ing to con­ceive depends on the indi­vid­ual sit­u­a­tion. It is par­tic­u­lar­ly rel­e­vant, for exam­ple, in the case of a known thy­roid con­di­tion, cor­re­spond­ing symp­toms, or abnor­mal pre­vi­ous find­ings.

• Thy­roid, TSH, and fer­til­i­ty when try­ing to con­ceive
• Ther­a­pies & treat­ment options
• Caus­es of a low or high TSH lev­el
• Symp­toms of hypothy­roidism
• Hashimoto’s thy­roidi­tis and try­ing to con­ceive
• Thy­roid dys­func­tion after preg­nan­cy

Thy­roid, TSH, and fer­til­i­ty when try­ing to con­ceive

TSH, T3, and T4: How thy­roid func­tion is reg­u­lat­ed

TSH (thy­roid-stim­u­lat­ing hor­mone) is pro­duced in the pitu­itary gland and reg­u­lates the pro­duc­tion of thy­roid hor­mones. If their con­cen­tra­tion in the blood decreas­es, more TSH is usu­al­ly released, stim­u­lat­ing the thy­roid to pro­duce the hor­mones T4 (thy­rox­ine) and T3 (tri­iodothy­ro­nine). If the con­cen­tra­tion of thy­roid hor­mones increas­es, TSH secre­tion decreas­es again.

This reg­u­la­to­ry loop is addi­tion­al­ly con­trolled by TRH (thy­rotropin-releas­ing hor­mone), which is pro­duced in the hypo­thal­a­mus. Because TSH responds sen­si­tive­ly to changes in thy­roid func­tion, it is the most impor­tant lab­o­ra­to­ry val­ue for an ini­tial assess­ment. If TSH is abnor­mal, addi­tion­al values—especially fT4—can be used for fur­ther clas­si­fi­ca­tion.

Rec­om­mend­ed TSH lev­els when try­ing to con­ceive and dur­ing preg­nan­cy

The TSH lev­el is mea­sured in the blood and assessed based on the ref­er­ence range of the respec­tive lab­o­ra­to­ry. A sin­gle cut-off val­ue does not apply equal­ly to every life sit­u­a­tion. Age, preg­nan­cy, and an exist­ing thy­roid con­di­tion can also play a role in the assess­ment.

Dur­ing preg­nan­cy, thy­roid func­tion changes, among oth­er fac­tors, due to the influ­ence of the preg­nan­cy hor­mone hCG. Accord­ing to the cur­rent Ger­man guide­line, a TSH lev­el of 4.0 mU/L is con­sid­ered the upper ref­er­ence lim­it if no suit­able region­al or lab­o­ra­to­ry-spe­cif­ic ref­er­ence val­ues for preg­nant women are avail­able. A TSH lev­el above 2.5 mU/L there­fore does not auto­mat­i­cal­ly mean that hypothy­roidism is present or that treat­ment is required.

When try­ing to con­ceive, too, a TSH tar­get val­ue below 2.5 mU/L does not apply across the board to every woman. The sit­u­a­tion may be dif­fer­ent, for exam­ple, in the case of already known and treat­ed hypothy­roidism. In such cas­es, low­er ther­a­peu­tic tar­get val­ues may be aimed for before and dur­ing preg­nan­cy. Clas­si­fi­ca­tion should there­fore always be based on the indi­vid­ual base­line sit­u­a­tion.

Thy­roid anti­bod­ies and Hashimoto’s: What mat­ters when try­ing to con­ceive

In Hashimoto’s thy­roidi­tis, the immune sys­tem tar­gets com­po­nents of the thy­roid. Typ­i­cal find­ings include anti­bod­ies against thy­roid per­ox­i­dase (TPO anti­bod­ies). Thy­roglob­u­lin anti­bod­ies (Tg anti­bod­ies) may also occur. TRAb (TSH recep­tor anti­bod­ies), by con­trast, main­ly play a role in Graves’ dis­ease.

How­ev­er, mea­sur­ing thy­roid anti­bod­ies is not gen­er­al­ly nec­es­sary for every woman when try­ing to con­ceive. What mat­ters are the indi­vid­ual med­ical his­to­ry, thy­roid func­tion, and exist­ing find­ings. A pos­i­tive TPO anti­body result also does not auto­mat­i­cal­ly mean that treat­ment with thy­roid hor­mones is nec­es­sary.

If TSH is ele­vat­ed, free T4 (fT4) and—depending on the findings—TPO anti­bod­ies are mea­sured in par­tic­u­lar for fur­ther clas­si­fi­ca­tion. Whether treat­ment with levothy­rox­ine is appro­pri­ate depends, among oth­er fac­tors, on whether overt or sub­clin­i­cal hypothy­roidism is present, how high the TSH lev­el is, and whether preg­nan­cy already exists or a thy­roid con­di­tion is being treat­ed.

For women with nor­mal thy­roid func­tion and pos­i­tive TPO anti­bod­ies, it can­not be gen­er­al­ly con­clud­ed that pre­ven­tive treat­ment with levothy­rox­ine improves fer­til­i­ty or preg­nan­cy out­comes. The deci­sion should there­fore be made on an indi­vid­ual basis.

Good to know: In Ger­many, test­ing for con­gen­i­tal hypothy­roidism is part of new­born screen­ing. For this pur­pose, among oth­er things, TSH is mea­sured from a dried blood spot in the first days of life.

Hypothy­roidism and sub­clin­i­cal hypothy­roidism: Ther­a­pies & treat­ment options

Hypothy­roidism is usu­al­ly treat­ed with levothy­rox­ine (L‑thyroxine). The med­ica­tion replaces the thy­roid hor­mone T4, which the body does not pro­duce in suf­fi­cient amounts in the case of under­ac­tiv­i­ty. The required dose is adjust­ed indi­vid­u­al­ly based on thy­roid val­ues.

In sub­clin­i­cal hypothyroidism—i.e., an ele­vat­ed TSH lev­el with nor­mal fT4—treatment is not required in every case. Whether levothy­rox­ine is appro­pri­ate depends, among oth­er fac­tors, on the lev­el of TSH, addi­tion­al thy­roid find­ings, and whether preg­nan­cy exists or is planned.

Women with already known and treat­ed hypothy­roidism should have their thy­roid val­ues checked, if pos­si­ble, before a planned preg­nan­cy. If there is an indi­ca­tion for treat­ment, levothy­rox­ine can and should also be con­tin­ued dur­ing preg­nan­cy. Because the need for thy­roid hor­mones often increas­es dur­ing preg­nan­cy, reg­u­lar mon­i­tor­ing is impor­tant and the dose may need to be adjust­ed.

Caus­es of a low or high TSH lev­el

A TSH lev­el out­side the ref­er­ence range may indi­cate altered thy­roid func­tion. For fur­ther clas­si­fi­ca­tion, the free thy­roid hormones—especially fT4—are tak­en into account.

A low TSH lev­el may indi­cate hyper­thy­roidism. Pos­si­ble caus­es include, for exam­ple:

• Graves’ dis­ease
• thy­roid auton­o­my, for exam­ple due to autonomous nod­ules

Graves’ dis­ease is an autoim­mune con­di­tion in which anti­bod­ies against the TSH recep­tor (TRAb) stim­u­late the thy­roid and can there­by trig­ger increased pro­duc­tion of thy­roid hor­mones. In addi­tion to the thy­roid, the con­di­tion can also affect oth­er organs, espe­cial­ly the eyes.

An ele­vat­ed TSH lev­el, by con­trast, may indi­cate hypothy­roidism. A com­mon cause is Hashimoto’s thy­roidi­tis, an autoim­mune dis­ease of the thy­roid. How­ev­er, whether there is actu­al­ly hypothy­roidism requir­ing treat­ment does not depend on the TSH lev­el alone.

Symp­toms of hypothy­roidism

Hypothy­roidism can present with var­i­ous, often non-spe­cif­ic symp­toms. Espe­cial­ly when try­ing to con­ceive or plan­ning a preg­nan­cy, it can be impor­tant to detect an exist­ing thy­roid con­di­tion ear­ly and treat it if nec­es­sary.

Pos­si­ble symp­toms of hypothy­roidism include:

• Fatigue
• dry skin
• con­sti­pa­tion
• mus­cle or joint pain
• increased sen­si­tiv­i­ty to cold and feel­ing cold more often
• con­cen­tra­tion and mem­o­ry prob­lems
• changes in the men­stru­al cycle

Because these symp­toms can also have many oth­er caus­es, hypothy­roidism can­not be diag­nosed based on symp­toms alone. For clar­i­fi­ca­tion, thy­roid val­ues are mea­sured in the blood.

Hashimoto’s thy­roidi­tis and try­ing to con­ceive

Hashimoto’s thy­roidi­tis is an autoim­mune dis­ease of the thy­roid. The immune sys­tem tar­gets com­po­nents of thy­roid tis­sue. Over time, thy­roid func­tion can decline and hypothy­roidism may devel­op. Typ­i­cal find­ings include ele­vat­ed TPO anti­bod­ies; thy­roglob­u­lin anti­bod­ies (Tg anti­bod­ies) may also be detectable.

Hashimoto’s is rel­a­tive­ly com­mon in women of repro­duc­tive age and can there­fore also play a role when try­ing to con­ceive. Thy­roid dys­func­tion can affect the cycle and fer­til­i­ty, among oth­er things. Stud­ies also show asso­ci­a­tions between autoim­mune thy­roid dis­ease and var­i­ous repro­duc­tive fac­tors. How­ev­er, the extent to which thy­roid autoimmunity—independent of thy­roid func­tion itself—affects fer­til­i­ty has not yet been con­clu­sive­ly clar­i­fied.

When try­ing to con­ceive, the key fac­tor is there­fore pri­mar­i­ly whether the thy­roid pro­duces suf­fi­cient hor­mones. If Hashimoto’s is asso­ci­at­ed with hypothy­roidism requir­ing treat­ment, it is treat­ed with levothy­rox­ine, and thy­roid lev­els should be checked already before preg­nan­cy. Pos­i­tive thy­roid anti­bod­ies alone, by con­trast, do not auto­mat­i­cal­ly mean that treat­ment with levothy­rox­ine is nec­es­sary.

Post­par­tum thy­roidi­tis: Thy­roid dys­func­tion after preg­nan­cy

Post­par­tum thy­roidi­tis is an inflam­ma­to­ry autoim­mune dis­ease of the thy­roid that can occur with­in the first year after child­birth. It affects about 5–10% of women after preg­nan­cy; it is more com­mon in cer­tain risk groups.

Typ­i­cal­ly, an ini­tial phase with ele­vat­ed thy­roid hor­mone lev­els may occur, fol­lowed by a phase of hypothy­roidism. How­ev­er, not all women go through both phas­es. Some expe­ri­ence only a hyper­thy­roid or only a hypothy­roid phase.

In the ear­ly phase, symp­toms such as pal­pi­ta­tions, rest­less­ness, sleep dis­tur­bances, or weight loss may occur. In the lat­er hypothy­roid phase, fatigue, weight gain, con­sti­pa­tion, dry skin, or depres­sive mood are pos­si­ble. Because some of these symp­toms are also com­mon in the post­par­tum peri­od, the con­di­tion is not always rec­og­nized imme­di­ate­ly.

Immuno­log­i­cal­ly, post­par­tum thy­roidi­tis resem­bles Hashimoto’s thy­roidi­tis and is often asso­ci­at­ed with TPO anti­bod­ies. Whether treat­ment is nec­es­sary depends on the phase and the sever­i­ty of symp­toms. In many women, thy­roid func­tion nor­mal­izes again with­in 12 to 18 months; how­ev­er, in some, per­ma­nent hypothy­roidism per­sists.