Some common health conditions can affect ovulation, sperm, and the health of a pregnancy. Many people with these conditions have healthy babies. The key is to find and manage them before you conceive, so your body is as ready as possible.
Why these conditions matter
The thyroid, the pancreas and the ovaries all help control hormones. When one is out of balance, it can affect periods, ovulation and early pregnancy. Most of these conditions can be checked with simple tests.
| Condition | Effect on fertility | Effect on pregnancy |
|---|---|---|
| Thyroid disease | Can stop ovulation | Untreated hypothyroidism raises miscarriage and pre-eclampsia risk |
| Diabetes | Needs planning before trying | Higher risk of miscarriage and a larger baby |
| Underweight | Irregular cycles; ovulation may stop | Discuss nutrition with your doctor |
| Obesity | Lower pregnancy rates; lower sperm counts in men | Higher risk of gestational diabetes and pre-eclampsia |
| High blood pressure | Medicines may need review | Higher risk of pre-eclampsia |
Thyroid disorders
The thyroid is a small gland in the neck that controls how your body uses energy. The NHS notes that both an overactive thyroid (hyperthyroidism) and an underactive thyroid (hypothyroidism) can prevent ovulation.
Thyroid hormone also matters in pregnancy. The American Thyroid Association explains that untreated hypothyroidism is linked to miscarriage and pre-eclampsia, and severe untreated hypothyroidism can affect the baby's brain development.
- A simple blood test (TSH) checks how your thyroid is working
- If you take thyroid medicine, your dose often needs to go up once you are pregnant, so contact your doctor as soon as you test positive
- Take thyroid tablets at least 4 hours apart from vitamins containing iron or calcium
Diabetes
High blood glucose around the time of conception and early pregnancy can affect a developing baby. The NHS lists higher risks of miscarriage and a larger baby, which can make birth more difficult.
- See your diabetes team earlyAsk for pre-pregnancy advice before you stop contraception.
- Work towards your HbA1c targetThe NHS suggests 48 mmol/mol (6.5%) or less if it is safe for you. Getting closer still helps.
- Take high-dose folic acidThe NHS advises 5 mg a day on prescription, until 12 weeks of pregnancy.
- Review medicines and checksSome tablets are switched to insulin. Eye and kidney checks are also recommended.
Weight: underweight and obesity
Weight is one factor among many, and it is never a matter of blame. ASRM explains that a BMI of 18.5 or less often causes irregular cycles and may stop ovulation.
With a BMI over 30, pregnancy rates are lower even when ovulation is regular, and the risks of gestational diabetes and pre-eclampsia are higher. In men, overweight is linked to lower sperm counts and motility.
Your doctor can help set a realistic goal that considers your age and health. Steady changes in eating and activity are usually more helpful than strict diets.
High blood pressure
Long-term (chronic) high blood pressure is a risk factor for pre-eclampsia, a serious pregnancy condition. CDC advises that treating high blood pressure is important before, during and after pregnancy.
Some blood pressure medicines are not suitable in pregnancy, while others are. Your doctor can help you switch to a safe option before you conceive.
Do not stop or start any medicine without talking to your doctor. Stopping suddenly can be more harmful than the medicine itself.
What to check before trying
Tests to ask about
Things to bring up
Working with your care team
If you live with one of these conditions, you may see more than one doctor, such as an endocrinologist, a physician and a fertility specialist. Sharing information between them helps everyone plan safely.
- Bring recent test results and a list of your medicines to each visit
- Tell every doctor that you are planning a pregnancy
- Ask how often your levels should be checked while trying and in early pregnancy
- Ask your partner to have a health check too
Numbers worth knowing
| Condition | What sources advise |
|---|---|
| Diabetes | HbA1c ideally no more than 48 mmol/mol (6.5%) before pregnancy; avoid trying above 86 mmol/mol (10%) (NHS) |
| Diabetes | Folic acid 5 mg daily, by prescription, until 12 weeks pregnant (NHS) |
| Hypothyroidism | Levothyroxine needs often rise 25–50% in pregnancy; thyroid tests about every 4 weeks in the first half (ATA) |
| Weight | BMI 18.5 or less often causes irregular cycles and may stop ovulation (ASRM) |
- Diabetic eye screening matters more in pregnancy, as the risk of serious eye problems rises.
- Tablets for diabetes are often switched to insulin; do not change medicines on your own.
- Both overactive and underactive thyroid can prevent ovulation (NHS).
Questions to ask at your visit:
- Are my current medicines safe for pregnancy, or should they be changed first?
- What HbA1c or thyroid result should I reach before trying?
- Do I need a higher dose of folic acid?
- Who should I contact as soon as I have a positive pregnancy test?
Targets are individual. Ask your doctor which numbers apply to you before you start trying.
When to see a doctor
- You have diabetes, thyroid disease or high blood pressure and are planning a pregnancy
- You have tried for 12 months if under 35, for 6 months if 35–39, or for less than 6 months if 40 or older
- Your periods are irregular or have stopped
- You have symptoms such as constant tiredness, weight change, feeling very hot or cold, or a fast heartbeat
- You are very thirsty or pass urine often
- You take thyroid medicine and have just found out you are pregnant
Questions & answers
Can I get pregnant if I have diabetes?
Yes. Many people with diabetes have healthy pregnancies, especially with planning and good glucose control beforehand.
Does my thyroid medicine affect fertility?
Correct treatment helps restore normal hormone levels. Keep taking it and let your doctor check your levels before and during pregnancy.
Do I have to reach a certain weight before treatment?
Not always. Your doctor will look at your whole situation, including age, and agree a plan with you.
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Sources
- Infertility: Causes — NHS
- Hypothyroidism in Pregnancy — American Thyroid Association
- Diabetes and pregnancy — NHS
- Weight and Fertility — ASRM ReproductiveFacts
- High Blood Pressure During Pregnancy — CDC
- Infertility: causes, diagnosis & treatment — Cleveland Clinic