Hypothyroidism and pregnancy

Thyroid physiology in pregnancy adapts to meet increased meta­bolic demands, and therefore women with pre-existing thyroid disease should be examined in the preconception period to opti­mize thyroid function.

In response to the rise in oestrogen in pregnancy, a corresponding almost twofold rise in serum levels of TBG is seen. The rise in TBG is a direct result of increased TBG production from increased levels of oestrogen, as well as decreased TBG clearance. To maintain free thyroid hormone levels, serum total thyroxine (T₄) and triiodothyr­onine (T3) concentrations also rise in the first half of pregnancy. Due to the homology of the beta-subunits of hCG and TSH, hCG con­tributes to thyroid stimulation through weak thyroid-stimulating activity.

Complications of maternal hypothyroidism include increased incidence of preterm labour, pre-eclampsia, placental abruption, perinatal morbidity and mortality, and neuropsychological and cognitive impairment (26-28). For these reasons, optimization of thyroid function in the preconception period is of utmost import­ance. In the preconception period, TSH should be optimized at less than 2.5 mU/L (29). Due to the changes seen in normal physiology in pregnancy, thyroid function tests should be interpreted with trimester-specific reference ranges, with lower acceptable ranges of TSH in the first trimester (2.5 mU/L), graduating to 3.0 mU/L in the second and third trimesters (29). Alternatively, another approach is to preconceptionally increase the dosing of levothyroxine; however, this should be done with close monitoring of TSH with goal TSH levels as described previously.

urea nitrogen, serum uric acid, serum electrolytes, urinalysis, as well as protein:creatinine ratio, and on an individual basis, a renal ultrasound scan.

There is controversial evidence to begin treatment in the precon­ception period for women with mild to moderate hypertension, de­fined as systolic blood pressure (SBP) of 140- 159 mmHg, or diastolic blood pressure (DBP) of 90-109 mmHg, with the number needed to treat to prevent severe hypertension ranging from 8 to 13 women (31). If there is any evidence of end-organ damage, antihypertensive therapy should be started immediately, regardless of blood pressure.

Antihypertensive therapy should be optimized in the precon­ception period. There is not a universal blood pressure goal, but recommended goals are less than 150 mmHg SBP and less than 100 mmHg DBP. Optimal antihypertensive agents include alpha­agonists (methyldopa), calcium channel blockers (nifedipine), and beta-blockers (labetalol). Angiotensin-converting enzyme (ACE) inhibitors should be avoided in the preconception period, as they have been shown to cause major congenital malformations with ex­posure in the first trimester (32).

Women should have a postpartum visit planned 6-8 weeks fol­lowing delivery, with standard postpartum care including blood pressure monitoring and weight measurement, with the goal of obtaining preconceptional weight within 6 months following delivery.

Women with previous pre-eclampsia

Women with a previous history of pre-eclampsia require increased monitoring starting at 20 weeks gestational age. The United States Preventative Services Task Force recommends that women iden­tified at high risk for pre-eclampsia take low-dose aspirin (81 mg daily) at 12 weeks gestational age as preventative medication (33). In this systematic evidence review, there was limited evidence of harms; however, an increased risk of placental abruption could not be ruled out (33). Although there was no evidence of increased risk of bleeding-related complications, including postpartum haemor­rhage, maternal blood loss, or neonatal intracranial haemorrhage, it is generally recommended to discontinue aspirin 2 weeks prior to delivery.