Approximately 6.1 million couples experience infertility each year, according to the American Society for Reproductive Medicine (ASRM). Surveys indicate about 15 percent of all couples will experience infertility at some time during their reproductive lives. When there are identi?able causes for infertility, it’s split evenly between male-factor and female-factor infertility. Roughly 20 percent of the time, the cause is unknown. The most common cause of infertility, however, is age. Table 8.1 indicates rates of fecundity (the ability to produce offspring) according to age. Age-related fecundity may be blamed when a thyroid disorder is the cause.
If you’re planning a pregnancy, start with a thyroid test to make sure that any problems with your cycles are not related to either hypothyroidism or hyperthyroidism. In addition, unrecognized thyroid disease can lead to miscarriage or fetal development problems. If your thyroid tests are normal prior to conception, you can rule out thyroid disease as a cause of infertility; if thyroid disease is discovered, you can restore fertility by treating it. If your thyroid is normal at conception, you should repeat TSH tests and thyroid antibody tests on the discovery of the pregnancy and have them checked monthly during your routine prenatal exams if the thyroid antibody tests are positive. Although not yet common practice, it’s reasonable that TSH tests be done at regular intervals on all fertile women (regardless of plans for pregnancy), because they could become pregnant and may not seek medical care until well into their pregnancy if they do have a thyroid problem.
If You Have Had Radioactive Iodine Therapy
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If you were treated for hyperthyroidism or thyroid cancer with radioactive iodine, you should plan not to get pregnant for about six months afterward, although there isn’t any de?nite evidence that pregnancy prior to this waiting period after RAI is harmful. There is one exception, which has more to do with hypothyroidism: if you were treated for thyroid cancer and were made hypothyroid for a treatment or a scan, you must wait until your thyroid hormone levels are normal before you try to conceive. Hypothyroidism in the early stages of fetal development can be harmful to the fetus. Otherwise, pregnancies should proceed normally as long as you’re taking suf? cient doses of your thyroid hormone replacement and your TSH level is monitored monthly; doses frequently need to be adjusted during pregnancy.
Normal Pregnancy Discomforts: How They Relate to Thyroid Disease
Common discomforts of pregnancy may mimic or mask hypothyroidism, which is why regular TSH testing is encouraged. If you are vomiting because of morning sickness, however, you may not be ingesting adequate amounts of iodine. The recommended total daily iodine intake should be 220 mcg per day for pregnant women and 290 mcg per day for lactating women. Dairy products are very high in iodine content, so if you’re meeting your calcium requirements, you’re probably ?ne.
The iodine in milk varies greatly (depending upon the season, the cow’s feed, and the location), averaging around 250 mcg per liter (60 mcg per cup). Prenatal vitamins, which most North American pregnant women take, contain at least 150 mcg of iodine per daily dose. If you take these vitamins with a glass of milk, you should be ?ne. If you’re unable to keep any liquids down, your physician should pay careful attention to all your nutritional needs, including iodine, to prevent malnutrition.
If you are suffering from severe morning sickness in early pregnancy, this may be a sign of gestational thyrotoxicosis, a transient form of thyrotoxicosis. It’s believed that morning sickness can become increasingly severe because of the overproduction of thyroid hormone.
Morning Sickness and Thyroid Hormone Replacement
Morning sickness also presents other problems for women who take thyroid replacement hormone (for preexisting or newly diagnosed thyroid diseases). Morning sickness may be mild, moderate, or severe. For more severe cases, the nausea and vomiting begins between six and eight weeks after your last menstrual period, persists strongly until about fourteen weeks after your last menstrual period, and then either disappears or gets much better. But it can persist well into the second trimester too and can even last the duration of the pregnancy.
If you are taking thyroxine, the problem with nonstop nausea and vomiting is that your thyroid hormone pill could be poorly absorbed, leaving you hypothyroid, which is dangerous to fetal health. If you are in doubt about whether your thyroid hormone pill came out with your breakfast, it’s probably all right to take an additional tablet as long as this isn’t too frequent an event. In extreme situations, your physician could give you your thyroxine medication as an injection into your muscle or under your skin.
Pregnancy and Preexisting Thyroid Disease
If you are hypothyroid or are taking thyroid hormone replacement for a thyroid condition diagnosed prior to your current pregnancy, it’s important to have your thyroid levels assessed monthly. Your target TSH level should be between 0.5 and 3 so that your dosages of thyroid hormone replacement can be appropriately adjusted, which is necessary for the growing fetus. Total T4 assessments are useless, since T4 naturally rises because of increased thyroxine-binding globulin (TBG); this is due to increased levels of estrogen during pregnancy. Although very little thyroid hormone will cross over from you to the baby, the little that does is very important, since normal thyroid hormone levels in you are critical for proper fetal development until your baby develops his or her own thyroid gland. Sometimes a change in dosage is needed because requirements for thyroid hormone can increase during pregnancy. It’s normal to require as much as a 30 to 50 percent increase in your dosage. Your doctor should monitor your TSH level and increase your dosage as necessary. Since prenatal vitamins often contain iron, it’s important to take them at night so that the iron doesn’t interfere with the absorption of your morning thyroid pill.
Pregnancy and Graves’ Disease
Taking anti-thyroid medication for Graves’ disease while pregnant is perfectly safe, and you should continue this medication so long as you’re under the supervision of a doctor. In fact, taking this medication may protect the baby in your womb from the effects of thyroid-stimulating antibody, which crosses from you into the baby’s circulation. The dosage of the anti-thyroid medication usually needs to be decreased during pregnancy for two reasons. First, your baby’s thyroid is more sensitive to these drugs than your own, and, second, Graves’ disease activity changes during the course of your pregnancy.
If you’re pregnant with active Graves’ disease that was newly discovered, you must start anti-thyroid drugs as soon as possible. You should remain slightly hyperthyroid so the baby’s thyroid antibodies can be properly suppressed.
If you are pregnant and have a history of previously treated Graves’ disease, there is still a risk that you could have a hyperthyroid baby because you may still be making thyroid-stimulating immunoglobulin (TSI). Without a working thyroid, you’ll never know, but TSI could still cross the placenta into the baby. In the case of previously treated Graves’ disease, you should request that your prenatal health care provider monitor the fetal heart rate during the pregnancy to look for signs that suggest fetal thyrotoxicosis; under rare circumstances, your health care provider may need a blood sample from the placenta to check thyroid hormone levels. If you’you’ve had a remission of Graves’ disease, fetal thyrotoxicosis should not be a risk.