The days of the ultrasound are some of the most exciting and memorable days of the pregnancy for many expectant mothers.

While checking the baby’s health is obviously the most important objective of that ultrasound, parents anticipate the ultrasound for other reasons as well.

The first ultrasound confirms the pregnancy and establishes a due date. That ultrasound also allows mom to see this baby she has been carrying around for the past seven or eight weeks or so…a rewarding and emotional experience even if the parents can’t make out exactly what they are seeing on that blurry, black and white screen. Typically, the next regularly scheduled ultrasound is the big day when parents find out if they are having a girl or boy.

Below are some important and interesting tidbits from Women’s Health Associates, an ob gyn in Missouri, that shed light on the ultrasound process and might help make the day more special for the parents.

How often is the ultrasound accurate in predicting gender? More than 99% of the time.

How early in the pregnancy can an ultrasound detect baby’s gender? This actually depends on the weight of the mother. For lighter mothers, the ultrasound can detect the gender as early as 17 weeks, while for heavier mothers, the ultrasound can detect the gender by the 22nd week.

Can the technician or doctor always tell you the gender in that second ultrasound? Not necessarily. If the baby’s legs are crossed or they are turned the wrong direction and refuse to move, then the ultrasound cannot pick up the gender.

Are there any tips to increase the likelihood the baby will get into position to detect the gender? If the baby is active, chances are they will move around during that ultrasound and at some point he or she will be in a position where the ultrasound can detect the gender. If the baby is sleeping inside the womb, they are less likely to move around.

Scheduling the ultrasound after breakfast or lunch, or eating a snack before the ultrasound will increase the likelihood the baby is active. Also, drinking water gives mother more fluid, which makes the ultrasound that much more clear and easier to detect.

How many parents choose to know the gender? The overwhelming majority of parents, roughly 90%, want to know. But in recent years, there has been an increasing number of parents who want the gender to be a surprise. This may be because so many other things are less of a surprise.

During the second ultrasound, what are some of the health issues the doctor is taking a look at? During this exam the doctor will look for heart defects. The doctor will also check whether the spine is straight, whether the baby has a cleft palate or club feet. Doctors will also see whether the baby might have hydrocephalus (a buildup of fluid inside the brain) and will also check to make sure there are two kidneys, and that they are the right size and in the right location.

What is a 3D ultrasound and how is it different from a 2D ultrasound? The 3D ultrasound sends sound waves toward the fetus at different angles, which are then reconstructed by the computer to form a 3D image of the fetus. The 2D ultrasound sends those sound waves at a single angle producing a 2D image. While Women’s Health Associates and most other ob gyn clinics can provide 3D ultrasounds, a 2D is still the most common ultrasound used and 3D ultrasounds are typically used only if a defect is detected in a baby.

While the 3D ultrasound is better at honing in on an area of the fetus and providing detail such as the size or depth of a particular abnormality, a 2D ultrasound is just as good at initially spotting those anomalies. While there is no conclusive evidence that ultrasounds are harmful for babies, doctors go with the 2D ultrasound for the normal checkup since that ultrasound does not take as long and thus exposes the baby to less ultrasound waves.