Thyroid function in pregnant mothers: prevention of late miscarriage
In the journey of surrogacy, there is no more heartbreaking scenario than fetal arrest in the late stages of a surrogate mother’s pregnancy. This sudden shock often hides an overlooked biological code – the delicate balance of thyroid function. A recent international cohort study of 5.84 million people reveals that a surrogate mother’s pre-pregnancy state of thyroid function, like the conductor of a symphony orchestra, quietly dominates the harmony of the pregnancy’s outcome.
The Thyroid Gland: The Surrogate’s “Navigational System for Life” on the Surrogacy Journey
Though small as a butterfly, the thyroid gland is the central commander of human metabolism and development. It secretes thyroid hormones (TSH, FT3, FT4) that not only regulate energy metabolism, but are also the “architects” of the embryo’s neurological development. Studies have shown that abnormal thyroid function increases the risk of miscarriage in surrogate mothers by 2-4 times, and is strongly associated with preterm labor, fetal growth restriction, and perinatal mortality.
Why is preconception thyroid management critical?
Golden window of fetal development: The fetal thyroid gland has not yet formed in early pregnancy, and neurological development is completely dependent on maternal thyroid hormones. If maternal hormones are out of balance at this time, irreversible intellectual damage may result.
The special characteristics of surrogacy: surrogate mothers are often due to hormone therapy or genetic background differences, thyroid function is more likely to fluctuate, requiring more precise pre-pregnancy regulation.
Data on 5.84 million people reveals: the “golden safety zone” of thyroid function.
In 2023, the International Center for Research in Reproductive Health (ICRH), in conjunction with scholars from multiple countries, published a landmark study in JAMA Network Open analyzing preconception thyroid data from 5.84 million surrogate mothers, clarifying for the first time:
Optimal preconception TSH range: 0.37-2.49 mIU/L, with the lowest risk of preterm birth, low birth weight, and perinatal death.
Risks follow a “J-curve”: the risk of adverse outcomes rises significantly with TSH <0.37 or >4.88 mIU/L, and is particularly high with TSH >10 mIU/L.
Metaphorical Implications
Thyroid function is compared to GPS navigation: stray too far from the “Golden Route” and the journey of life will be marred by unpredictable storms.
Thyroid management strategies for surrogate mothers
- Pre-conception screening: building the first line of defense
Required indicators: TSH, FT4, TPOAb (Thyroid Peroxidase Antibody). even if the hormones are normal, the risk of miscarriage is still 3 times higher for TPOAb positive patients.
Timing of screening: 3-6 months prior to the signing of the surrogacy agreement to ensure sufficient time to adjust the treatment program.
- Tiered intervention: a model for precision medicine
Subclinical hypothyroidism (TSH 2.5-4.87 mIU/L): no need for excessive intervention, but monthly monitoring is required.
Clinical hypothyroidism (TSH ≥ 4.88 mIU/L): immediately initiate levothyroxine (L-T4) therapy with a target TSH ≤ 2.5 mIU/L.
Positive thyroid antibodies: even if hormones are normal, small-dose L-T4 prophylaxis is recommended to reduce the risk of immune rejection.
- Dynamic monitoring: guarding throughout
Early pregnancy: TSH every 4 weeks, as hCG hormone may interfere with the thyroid axis6 .
Middle and late pregnancy: retest every 8-12 weeks, focusing on the risk of postpartum thyroiditis in TPOAb-positive individuals.
Clinical Case: When Science Lights the Way to Hope
Case 1: Emily’s Turnaround
Emily, an American surrogate mother, had a pre-pregnancy TSH of 5.8 mIU/L (TPOAb positive) and experienced two fetal arrests. After L-T4 treatment to reduce TSH to 1.8 mIU/L, the third surrogate successfully delivered healthy twins.
Case 2: Sophia’s warning
Spanish surrogate mother Sophia, who had a pre-pregnancy TSH of 0.2 mIU/L (uncontrolled hyperthyroidism), had a sudden onset of fetal growth restriction during pregnancy. Studies have shown that the rate of preterm labor in untreated hyperthyroidism is as high as 30%.
Beyond conventional wisdom: the “invisible battleground” of thyroid function
- Thyroid antibodies: the silent “immune landmine”.
TPOAb positivity suggests a risk of autoimmune attack, which may jeopardize the pregnancy even if the TSH is normal, through the following mechanisms:
Placental inflammation: the antibodies trigger an immune imbalance at the maternal-fetal interface, interfering with embryo attachment8.
Hormonal resistance: similar to “the key that doesn’t unlock the door”, cells are unable to utilize thyroid hormones effectively. 2.
- Environmental toxins: the invisible killers of modern life
Endocrine disruptors such as bisphenol A (BPA) and phthalates can mimic the structure of thyroid hormones and disturb the hormonal balance of the surrogate mother. It is recommended to avoid potential toxins in plastic containers and cosmetics before pregnancy.
Global Consensus and Controversies: Balancing Science and Individualization
- The TSH Threshold Debate
American Thyroid Association (ATA): recommends TSH control at <2.5 mIU/L before surrogacy.
European guidelines: more lenient, allowing TSH ≤4.0 mIU/L, emphasizing individualized assessment.
- Innovations in the timing of intervention
The traditional view is that intervention during pregnancy is sufficient, but new studies confirm that thyroid status in the first 6 months of pregnancy determines embryo quality. Like improving the soil before planting, it is more critical than applying fertilizer later.
Accurate prediction
Comprehensive preconception screening: thyroid function should be listed as “mandatory” rather than “optional” for surrogate mothers.
Selection of experienced team: Priority should be given to organizations that have the ability to provide multidisciplinary consultations in endocrinology and reproductive medicine.
Psychological support: Thyroid treatment takes several months, and psychological counseling can ease anxiety and improve compliance.
Humanistic thinking
Every fetal arrest is a question of life to science. Through the fine regulation of thyroid function, we not only guard the physical existence of the embryo, but also defend the infinite possibilities of a future life.
