What are the thyroid diseases during pregnancy and childbirth? What are the effects on the mother, fetus and offspring?

Thyroid disease is a common condition
in pregnant women.
The prevalence of thyroid dysfunction in non-gestational age women in China is 17.
2%.

Because pregnancy is affected by human chorionic gonadotropin (hCG), thyroxine binding globulin (TBG) and other factors, the diagnostic criteria for thyroid disease in pregnant women need to use the reference range of pregnancy-specific TSH and thyroxine (T4).
Therefore, the prevalence of thyroid disease in pregnant women is different
from that in women of non-reproductive age.

Thyroid disease and iodine nutrition during pregnancy and childbirth

Effects on the mother, fetus and offspring

1.
Hypothyroidism

Hypothyroidism increases the risk of infertility in women of
childbearing age.
Maternal hypothyroidism, if not effectively treated, increases the risk of hypertensive disorders during pregnancy, miscarriage, preterm birth, low birth weight and even stillbirth, and jeopardizes the neurointellectual development
of offspring.
Subclinical hypothyroidism during pregnancy and labor also increases adverse pregnancy outcomes
.
The risk of miscarriage increases gradually as TSH levels increase in the first trimester, and if TPOAb or TgAb is positive, the risk of miscarriage increases
further.
Subclinical hypothyroidism during pregnancy and childbirth may affect the intellectual and motor development
of offspring.
Effective treatment of subclinical hypothyroidism if effectively treated in the first trimester, especially before eight weeks' gestation, is beneficial
in reducing the risk of miscarriage and improving the intelligence of offspring.

2.
Hyperthyroidism

Poorly controlled hyperthyroidism during pregnancy and labour is associated with gestational hypertension, miscarriage, preterm birth, low birth weight infants, intrauterine growth restriction, stillbirth, thyroid storm, and congestive heart failure; This may result in decreased intelligence in children and a decrease in gray matter volume in the cerebral cortex, and an increased
risk of epilepsy and neurobehavioral abnormalities in offspring.
Elevated T4 can enter the fetus through the placenta, thereby inhibiting the secretion of fetal pituitary TSH, resulting in fetal hyperthyroidism and transient central hypothyroidism
in newborns.

3.
Hypothyroxinemia

Hypothyroxinemia in pregnant women is associated with macrosomia, preterm birth and gestational diabetes, and hypertension, and may increase the risk
of mental decline, autism, and attention-deficit/hyperactivity disorder in offspring.
Fetal brain development depends on maternal T4 in the first trimester, so LT4 therapy
can be used while actively searching for the cause.

4.
Positive thyroid autoantibodies

Positive thyroid autoantibodies (TPOAb and TgAb) are the leading cause of hypothyroidism during pregnancy and childbirth and are risk factors
for miscarriage, preterm birth, and prenatal rupture of membranes.
LT4 treatment reduces the risk
of miscarriage and preterm birth in TPOAb-positive pregnant women.
However, in pregnant women undergoing assisted reproduction due to infertility, LT4 therapy does not improve assisted reproductive outcomes
if the thyroid function is normal and the thyroid autoantibody alone is positive.

5.
Iodine deficiency

Severe iodine deficiency in pregnant women can increase miscarriage, stillbirth, and postnatal infant mortality, leading to cretinism.

Mild to moderate iodine deficiency increases the risk of goiter and thyroid disease, which may adversely affect
the cognitive function of offspring.
In areas with severe iodine deficiency, iodine supplementation in pregnant women can reduce fetal stillbirths, neonatal and infant mortality, and improve the intelligence
of offspring.
Iodine supplementation in early pregnancy in women in areas with mild to moderate iodine deficiency may improve neurological development
in children.
If LT4 supplementation alone does not improve the intelligence of the offspring if only LT4 is supplemented without iodine supplementation in pregnant women with iodine deficiency
.

Thyroid disease during pregnancy and childbirth

Relevant definitions and diagnostics

1.
Basis for diagnosis

Thyroid disease during pregnancy and postpartum is diagnosed according to the reference range of serum TSH, free thyroxine (FT4), and free triiodothyronine (FT3) in the general population, and the detection exceeds the normal range, considering the possibility
of thyroid disease.
The pregnancy period should be diagnosed
according to the specific serum TSH, FT4 and FT3 reference range of early, middle and late pregnancy.
Normal thyroid function means that TSH, FT4, and FT3 are in the normal range
.
A negative thyroid autoantibody means that both TPOAb and TgAb are in the normal range
.

2.
Definition and diagnosis of common thyroid diseases during pregnancy and childbirth

TPOAb or TgAb-positive autoimmune thyroiditis, hypothyroidism, hyperthyroidism, thyroid nodules, and thyroid cancer are common
in women trying to conceive and during childbirth.
In addition, common, and interesting thyroid dysfunction specific to pregnancy and childbirth includes high normal TSH, hypothyroxinemia, and transient thyrotoxicosis
of pregnancy.
Definitions and diagnostic criteria for common thyroid disorders during pregnancy and childbirth are detailed in the table below
.