At Merck China Forum 2015, Prof. John Lazarus of Cardiff University, UK, a renowned expert in the field of thyroid disorders in pregnancy, gave a fascinating presentation titled “Abnormal Thyroid Function in Pregnancy: An Update on Progress”, highlighting the latest developments in thyroid dysfunction in pregnancy in terms of the risks to mothers and babies, as well as the recommendations of current authoritative guidelines/societies on whether routine screening of thyroid function in pregnancy should be performed. The presentation focused on the latest advances in the risks of abnormal thyroid function in pregnancy for both mother and child, as well as the current recommendations from authoritative guidelines/societies on whether or not to routinely screen for thyroid function in pregnancy. Some of the highlights are summarized for the benefit of the readers. It is well established that fetal brain development is dependent on adequate thyroid hormones, and many studies have shown that hypothyroidism in pregnancy increases the risk of adverse pregnancy outcomes and can have adverse effects on fetal neurointellectual development. Although there is a lack of consistent research on the effects of hypothyroidism in pregnancy on mothers and infants, there is evidence from national and international studies suggesting that hypothyroidism in pregnancy is associated with an increased risk of miscarriage, gestational diabetes mellitus, hyperemesis gravidarum, preeclampsia, and preterm labor in pregnant women. The link and mechanism between subclinical hypothyroidism in pregnancy and impaired neurointellectual development in the offspring are uncertain, and may be associated with the risk of impaired visual development, delayed neurodevelopment and behavioral problems in the offspring. Offspring of untreated pregnant women with subclinical hypothyroidism may have delayed expressive language, mental retardation, poor cognitive functioning, and an increased risk of autism. In addition, the presence of thyroid peroxidase (TPO) antibodies is a risk factor for miscarriage, progression of hypothyroidism, preterm labor, impaired child development, and postpartum thyroiditis. An RCT found that L-T4 treatment of thyroid autoantibody-positive pregnant women with normal thyroid function resulted in a significant reduction in the incidence of miscarriage. However, due to the limitations of the study itself, the question of whether treatment reduces the risk of miscarriage remains controversial. It is still believed that there is no evidence for or against the use of levothyroxine therapy in women with normal thyroid function, including women with a history of episodic or recurrent miscarriage. Studies have shown that L-T4 treatment given for hypothyroidism and hypothyroxinemia in pregnancy provides significant benefits: reduced rates of adverse events in the mother and offspring and no effect of treatment on the offspring’s neurodevelopment at age 3 years; and decreased rates of miscarriage and preterm birth in patients with TPO-antibody-positive pregnancies who receive the treatment. The evidence on whether routine screening for hypothyroidism in pregnancy is warranted is unclear, and Prof. John Lazarus suggests that it may be reconsidered when new high-quality data become available. There is currently no evidence to support the need for routine screening for hypothyroxinemia. Based on current evidence-based medicine, the American Thyroid Association (ATA) does not believe there is sufficient evidence for or against routine TSH screening. The American Endocrine Society (ENDO) is not in agreement about routine screening of all pregnant women at their first visit, with some members recommending that all pregnant women be screened for serum TSH before 9 weeks’ gestation or at the initial visit, and some members neither supporting nor opposing routine TSH screening of all pregnant women at their first visit, but all members strongly support the need to aggressively seek out and test for TSH levels in high-risk women. Bio.