Preparing for a successful pregnancy with a thyroid condition

pregnancy with a thyroid condition
on Thu 4 Jan



If you have an undiagnosed thyroid condition it may make it difficult to conceive and can potentially cause some problems during pregnancy.  So if there is any family history of thyroid problems;  or you have an irregular menstrual cycle;  or it has taken more than 6 months to conceive you may want to check for any potential symptoms on these patient advice sheets and consider getting tested.


If you’ve already been diagnosed with a thyroid condition, there’s no reason why you shouldn’t have a healthy pregnancy and baby.  However, it’s important to let your doctor know a few months in advance of trying for a baby so that you can work together to optimise your outcomes before and during pregnancy.


If you think you’ve conceived before taking the advice of your GP don’t panic.  Your risk of complications will only be slightly higher than usual.  Just let them know as soon as possible.   


Thyroid levels

Before conception it’s currently recommended that your TSH (thyroid stimulating concentration) should ideally be kept in the lower half of the reference range (between 0.5 and 2.5 mU/L) as this has been associated with a lower risk of miscarriage.


During the first trimester (12 weeks), the healthy brain development of the foetus is very much dependent on the mother’s thyroid hormones so careful monitoring is advised. During pregnancy your levels should ideally be kept below 2.0 mU/L which may require a dose adjustment in your medication in order to mimic the body’s natural increase of thyroid hormones by as much as 50%.


For women with an underactive thyroid (hypothyroidism) it‘s perfectly safe to take Levothyroxine during pregnancy and it’s not unusual for your dose to be increased by between 25 to 50 mcg daily at this time.


With regard to women with an overactive thyroid (hyperthyroidism), Propylthiouracil (PTU) is usually considered the preferred drug in early pregnancy as it is less likely to cross the placenta than carbimazole (CMZ).  However, it is often changed back to carbimazole in later months as there have been rare reports of liver toxicity in young children.


Regular blood tests should be taken throughout pregnancy with TSH levels being measured monthly to keep your thyroid levels as required.


Iodine levels

If you have normal thyroid function, your need for iodine increases during pregnancy so you will still be recommended to have prenatal vitamins that will typically include iodine, folic acid and vitamins D and B12.


Supplements and Levothyroxine

If you are prescribed supplements which include iron, calcium or are taking Gaviscon you should wait three to four hours before or after your levothyroxine as they can affect absorption. This applies to your prenatal vitamins if they contain iron or calcium too. There is no need to take additional iodine if you are already taking Levothyroxine.


Graves’ disease and pregnancy

Men are advised to wait for 4 months before fathering a child if they have had radioiodine treatment.  Women are advised to wait for 6 months before becoming pregnant after radioiodine treatment.


Although your thyroid function may be normal on Levothyroxine after being successfully treated by surgery or radioiodine, there may still be Graves’ disease antibodies in the blood (called the TSH receptor antibodies) even if your condition is well under control.  


These antibodies can cross the placenta and cause temporary symptoms of Graves’ disease in the baby during the second half of pregnancy and for up to 2-3 months after delivery.


By measuring the level of this antibody early in the pregnancy you can be guided as to whether this is likely to be a problem in your pregnancy. The heart rate and growth rate of the developing baby in the womb can also indicate if there is a potential problem.


I hope you found this helpful. Please read my next post about morning sickness and pregnancy - you might be surprised to learn that this is endocrine related.


Although every effort is made to ensure that all health advice on this website is accurate and up to date it is for information purposes and should not replace a visit to your doctor or health care professional.


As the advice is general in nature rather than specific to individuals Dr Vanderpump cannot accept any liability for actions arising from its use nor can he be held responsible for the content of any pages referenced by an external link


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