Thyroid and Infertility in Women: What You Need to Know

Thyroid and Infertility in Women

Thyroid disorders are one of the most common and most treatable causes of female infertility. Yet they are frequently overlooked in fertility evaluations. If you are struggling to conceive, thyroid testing is essential.

The Thyroid-Fertility Connection

Thyroid hormones are essential for:

• Normal ovulation
• Endometrial development and implantation
• Early embryo development
• Maintaining pregnancy in the first trimester

Even subtle thyroid dysfunction can disrupt these processes and impair fertility.

How Hypothyroidism Affects Fertility

Ovulation: Hypothyroidism elevates prolactin levels (hyperprolactinemia), which suppresses ovulation. Many women with hypothyroidism have irregular or absent ovulation.

Implantation: Thyroid hormones are needed for proper endometrial development. Low levels impair the uterine lining's ability to support implantation.

Early pregnancy: Thyroid hormones are critical for fetal brain development in the first trimester, before the fetal thyroid is functional. Maternal hypothyroidism increases miscarriage risk.

TSH targets for fertility:

• General population: 0.4–4.0 mIU/L
• Women trying to conceive: < 2.5 mIU/L
• During pregnancy: < 2.5 mIU/L (first trimester)

How Hyperthyroidism Affects Fertility

• Disrupts the menstrual cycle (irregular or absent periods)
• Impairs ovulation
• Increases miscarriage risk
• Can cause premature birth if untreated during pregnancy

Thyroid Antibodies and Fertility

Women with thyroid antibodies (TPO or TgAb) — even with normal TSH — have:

• Higher risk of miscarriage
• Higher risk of IVF failure
• Increased risk of postpartum thyroiditis

Thyroid antibody testing should be part of every fertility workup.

Diagnosis

• TSH, Free T4, Free T3
• TPO antibodies, TgAb
• Thyroid ultrasound if indicated

Treatment

Hypothyroidism: Levothyroxine to achieve TSH < 2.5 mIU/L before conception. Dose is increased during pregnancy.

Hyperthyroidism: Antithyroid drugs (PTU preferred in first trimester), with careful monitoring.

Subclinical hypothyroidism with antibodies: Many specialists recommend levothyroxine treatment even with normal TSH if antibodies are positive and the patient is trying to conceive.

Conclusion

Thyroid testing should be routine in any woman with infertility, recurrent miscarriage, or irregular periods. Treatment is simple and highly effective.

At GyneNepal, Dr Sanjay Kumar Thakur provides comprehensive thyroid evaluation as part of our fertility workup. Book a consultation or learn more about Infertility Treatment and our Thyroid Specialist.