Hypothyroidism in Pregnancy

Thyroid hormones are vital to keep you well and for the development of your growing baby, especially their brain and nervous system. Pregnancy pushes thyroxine levels down, so you will need your levothyroxine dose increased. Levothyroxine is safe to take during pregnancy and breastfeeding - take it on an empty stomach and at a different time to any vitamin or mineral supplements you are taking.

Unfortunately, if thyroid function is not kept under tight control, it does carry risks to you and your baby, including pre-eclampsia, miscarriage or stillbirth, preterm birth (before 37 weeks), low birth weight, birth defects, and problems with the baby’s physical and mental development. It may cause an underactive thyroid in the baby.

Your doctor will refer you to a hospital specialist, or endocrinologist, as soon as pregnancy is confirmed, and they will monitor you closely.

To start with, good control of thyroid function is essential for fertility in both men and women. The earlier you seek advice, the better. Ask your doctor for a thyroid function test when you’re planning to conceive, to optimise treatment according to your levels for your forthcoming pregnancy.

Form a plan in advance with your doctor about increasing your levothyroxine once you know you are pregnant. Once you know you are pregnant, let them know so they can organise further blood tests at the start of pregnancy. They will refer you to an endocrinologist for further monitoring.

As pregnancy reduces levels of thyroxine, hypothyroidism would get worse through pregnancy if the dose of levothyroxine wasn’t increased from the start, and if it wasn’t changed in response to blood tests throughout. Levels usually stabilise in the later stages of pregnancy, so your specialist may decide to reduce the frequency of blood tests from the initial four to six weeks.

Most women return to pre-pregnancy thyroid function after birth – your thyroid should be checked around six weeks after delivery and medications may be adjusted then.

All women should take folic acid and vitamin D supplements when thinking about becoming pregnant and for the first three months of pregnancy. To ensure optimum health of your growing baby, it's recommended that every woman stops smoking, if applicable, and limits alcohol. You should keep hydrated, especially as pregnancy increases requirements, and follow a diet full of fresh fruit and vegetables, whole grains and fibre. Maintaining gentle activity levels, as able, and making sure you are getting enough rest and relaxation time will help all body systems while your body changes and adapts.

All of this will help you stay healthy and in tune with your body, so you can be more alert if symptoms creep in.

Unfortunately, there is nothing specific that you can do to control your thyroid function, except make sure you don’t miss out medications and keep up with all your thyroid function tests. If vomiting is persistent or prolonged, you should discuss this with your specialist, as medication may not have a chance to be absorbed into your system.