Subtotal thyroidectomy can be performed after thyrotoxicosis is medically controlled. This seldom is done during pregnancy but may be appropriate for the very few women who cannot adhere to medical treatment or in whom drug therapy proves toxic (Stagnaro-Green, 2012a). Surgery is best accomplished in the second trimester. Potential drawbacks of thyroidectomy include inadvertent resection of parathyroid glands and injury to the recurrent laryngeal nerve.
Thyroid ablation with therapeutic radioactive iodine is contraindicated during pregnancy. The necessary doses may also cause fetal thyroid gland destruction. Thus, when radioactive iodine is given unintentionally, many clinicians recommend abortion. Any exposed fetus must be carefully evaluated, and the incidence of fetal hypothyroidism depends on gestational age and radioiodine dose (Berlin, 2001). There is no evidence that radioiodine given before pregnancy causes fetal anomalies if enough time has passed to allow radiation efects to dissipate and if the woman is euthyroid (Ayala, 1998). The International Commission on Radiological Protection has recommended that women avoid pregnancy for 6 months after radioablative therapy (Brent, 2008). Moreover, during lactation, the breast also concentrates a substantial amount of iodine. This may pose neonatal risk due to I-containing milk ingestion and maternal risk from significant breast irradiation. To limit the latter, a delay of 3 months after breastfeeding cessation will more reliably ensure complete breast involution.
Pregnancy Outcome. Women with thyrotoxicosis have pregnancy outcomes that largely depend on whether metabolic control is achieved. For example, excess thyroxine may cause miscarriage or preterm birth (Andersen, 2014; Sheehan, 2015). In untreated women or in those who remain hyperthyroid despite therapy, incidences of preeclampsia, heart failure, and adverse perinatal outcomes are higher (Table 58-2). A prospective cohort study from China showed that women with clinical hyperthyroidism had a 12-fold greater risk of delivering an infant with hearing loss (Su, 2011).
In most cases, the perinate is euthyroid. In some, however, hyper-or hypothyroidism can develop with or without a goiter (Fig. 58-3). Clinical hyperthyroidism develops in up to 1 percent of neonates born to women with Graves disease (Barbesino, 2013; Fitzpatrick, 2010). If fetal thyroid disease is
TABLE 58-2. Pregnancy Outcomes in Women with Overt Thyrotoxicosis aData presented as n (%). Data from Davis, 1989; Kriplani, 1994; Luewan, 201n1; Medici, 2014; Millar, 1994.
FIGURE 58-3 Term hypothyroid neonate delivered of a woman with a 3-year history of thyrotoxicosis that recurred at 26 weeks' gestation. The mother was given methimazole 30 mg orally daily and was euthyroid at delivery.
suspected, nomograms are available for sonographically mea sured thyroid volume (Gietka-Czernel, 2012).