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If the pregnancy tests and ultrasound scans have confirmed the presence of pregnancy including viability (presence of heartbeat), then pregnancy can be considered as confirmed. Go ahead with getting serial HCG level estimation done. 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/threatened abortion. Visit your doctor/gynecologist at the earliest for further evaluation and assistance. You can also consider getting another ultrasound scan done by another radiologist. Look out for danger signs like increase in intensity of abdominal cramps, increasing back pain, fresh bleeding etc. Be in regular monitoring and follow-up with your treating doctor/gynecologist and report any new/abnormal symptoms immediately. Take adequate rest. Drink plenty of water. Maintain healthy diet.
Take care.