Viability scan is one of the more important scans in the pregnancy. It should be performed between 4-8 weeks of pregnancy. The earliest it can be performed is one week after missing the period. It usually can be performed with the usual trans abdominal scan. The trans vaginal scan is the recommended technique giving very clear images and providing for earlier diagnosis as compared to the trans abdominal technique.
A properly performed viability scan should provide the following information regarding the pregnancy:
Dating the pregnancy is essential for every pregnancy. Most women who conceive will remember their last menstrual date rather precisely. Even with precise account of the last menstrual date the ultrasound scan will re-assign a new expected delivery date in more than 20%. The ultrasound scan is very precise in this and comes close to a 3 days margin of error in predicting the due date accurately. Small errors in assignment of the expected delivery (due) date is probably alright. Larger error margins can be harmful as most decisions by obstetricians (gynae) are based on the expected delivery date.
Ectopic pregnancy is a life-threatening condition as the pregnancy usually get located in one of the fallopian tubes (right more than left). Life threatening bleeding can happen If it ruptures the tube. It used to occur in 0.5% of pregnancy. With fertility treatment more common and more women going through assisted conception the rate of ectopic pregnancies is increasing. Ectopic pregnancy is also more common after an episode of sexually transmitted infection in females. This is more common after unprotected sexual intercourse with multiple partners.
Twin pregnancy is also on the rise. Although this is perceived as good news twins are considered high risk pregnancies. Twin pregnancies are more common in those with family history of twins, maternal age of 30 or more and those who conceived after taking fertility treatments. The most important factor to be determined is if the twin is of the identical (monochorionic) or non-identical type (dichorionic) type. This can be easily determined prior to the 14th week of pregnancy but becomes increasingly more difficult to differentiate beyond 16 weeks.
Miscarriage is rather common. One in 8 pregnancies miscarry in the first trimester (1st 3 months). Most miscarriages make themselves evident with vaginal bleeding and pain. A proportion of miscarriages occur silently. The fetal stops stops beating without any symptoms. Miscarriage is more common in the following groups: advanced maternal age >30, medical conditions, conception after fertility treatment, thrombophilia. After an episode of bleeding in the 1st 3 months, it is important to have a viability scan to determine if the fetal activity is present and if there is any collection of blood under the placenta. If fetal heart is present and the placenta is normal there is a 95% chance the pregnancy will continue.
Ovarian cysts. These are common. 10% of pregnancies will have identifiable cysts in the ovaries. These are normal as long as there is no pain and the size is not in excess of 5 cm. Rarely a large cyst is identified. This will need to be surgically removed later in pregnancy. Only 0.1% of ovarian cyst in pregnancy is malignant.
Fibroids are very common. 20% of women unknowingly carry them. They do not always cause symptoms. If identified in pregnancy it simply needs to be observed with time. It may enlarge in pregnancy. Occasionally fibroids can cause pain, especially in pregnancy. Fibroids can be detected by a detailed ultrasound scan in the first 3 months.