Ultrasounds are a part of standard prenatal care in the United States. Most of the estimated 6 million women who become pregnant every year in the United States have at least one ultrasound, which typically is done at approximately 20 weeks of gestation. However, there are multiple instances when a second ultrasound may be ordered by the professional. These involve fetal viability, age, position and other factors.
Viability
Women often have a primary ultrasound in the first trimester in order to confirm that conception has taken place. Women who have undergone any type of artificial insemination procedure may have this ultrasound done as soon as the embryo would be visible on ultrasound. However, if the ultrasound is done this early, it can be difficult to determine the viability of the fetus because of its positioning and size. A second ultrasound thus may be done after the primary ultrasound in order to ensure that the fetus is healthy and has a strong heartbeat.
Defects
If a doctor does a routine 20-week ultrasound and finds a reason for concern about the baby, he may schedule an additional ultrasound to confirm a suspected problem and to develop a treatment plan. For instance, if an ultrasound showed a potentially life-threatening problem with a heart valve, a second ultrasound could be used to look more closely at the defect so the doctor and parents could decide if surgery would be necessary after the birth. Similarly, a doctor might look closely at a cleft palette or lip through a second ultrasound so she could advise the parents on the seriousness of the defect and whether cosmetic surgery might be a good option.
Gender
Many parents want to know if their baby is a boy or a girl, and they usually can find out the gender (if desired) at the 20-week ultrasound. However, sometimes the baby is not positioned in such a way that this is possible. In such cases, if the parents are adamant about knowing the gender, the doctor may consent to scheduling a second ultrasound so that the parents can find out if they are having a girl or a boy.
Due Date
A doctor usually uses a primary ultrasound to give parents an approximate due date for the baby. Sometimes, however, the mother later may appear to be measuring large for the due date that was given originally. The doctor may opt to schedule a second ultrasound to confirm the size of the baby so that a due date can be adjusted if needed.
Positioning
The position of the baby and the placenta are crucial in a healthy delivery. If the baby is breech, for instance, delivery often is harder and longer. If the placenta is below the baby and blocking the vaginal opening, a cesarean section may be needed because birthing the placenta first gives the baby only a few moments to be born before becoming deprived of oxygen. If a woman has a history of breech births, or if she is suspected of having a placenta position that could put the baby at risk, her doctor may confirm the position of the baby or placenta with another ultrasound before attempting delivery.
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