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If the thyroid levels are controlled well, it should not affect pregnancy chances. If you have missed your periods, and if you suspect chances of pregnancy, consider visiting your doctor/gynecologist at the earliest for thorough examination (to confirm pregnancy related changes/signs in body) and blood/serum HCG level test (to confirm/rule out pregnancy accurately). If you have had previous early miscarriage, if pregnancy gets confirmed, consider getting serial HCG levels estimated. Doubling up of the hormone levels in 48-72 hours will show that pregnancy is going on smoothly. If levels are not adequate, then external hormonal supplements would be considered to be started to help you in preventing miscarriage. Be in regular monitoring and follow-up with your treating doctor/gynecologist and report any new/abnormal symptoms immediately. Drink plenty of water. Take adequate rest. Maintain healthy diet and lifestyle. Look out for danger signs like increase in intensity of abdominal cramps, increasing back pain, fresh bleeding etc. Avoid lifting any heavy weights and avoid heavy work. Avoid standing for long durations and avoid climbing stairs. Avoid use of caffeinated and carbonated beverages.
Take care.