Ultrasounds are standard for every pregnancy because they’re an effective way for doctors to monitor the health of both the growing fetus and mother-to-be.
In general, a healthy pregnancy should involve two ultrasounds: one in the first trimester and another mid-way through the second trimester.
However, each pregnancy is different and you may require more ultrasounds based on factors including age, weight, and medical history.
Here’s what you need to know about when to get an ultrasound, what to expect during your appointment, and why you might need more than the standard two ultrasounds.
True to its name, an ultrasound works by sending and detecting sound waves. An OB-GYN or an ultrasound technician uses a device called a transducer to send sound waves through the skin into the womb. The sound waves bounce off the fetus to create an image of the baby in the womb.
While getting ultrasound pictures is considered an early milestone for many parents, the primary purpose of an ultrasound is not for a keepsake. Doctors use this time to check on the baby’s development, detect any genetic abnormalities, and examine the uterus, placenta, and amniotic fluid.
Generally speaking, ultrasounds are safe to perform during pregnancy, but in terms of how many to plan for, it’s important to talk to your doctor to establish clear medical reasons as to why an ultrasound is needed.
“An ultrasound does not involve radiation, and, at the frequencies used for diagnostic imaging, poses no known risk to the mother or developing baby,” says Dr. Stephen Chasen, director of obstetric imaging at NewYork-Presbyterian and Weill Cornell Medicine.
If you have a healthy pregnancy, you’ll typically only need two ultrasounds. The first one is usually scheduled for late in the first trimester, around the 11 to 14-week mark. If the pregnancy has no major complications, the second ultrasound comes at about 18 to 20 weeks.
What to expect from the first trimester ultrasound
Many women experience their first ultrasound between 11 to 14 weeks into their pregnancy. With this examination, also known as a “dating ultrasound,” the doctor will evaluate gestational age and rule out or identify any major abnormalities in early development.
During this early ultrasound, you can expect the doctor to:
- Confirm the pregnancy: This is done by checking the fetal heartbeat.
- Establish a due date: By measuring the fetus, doctors are able to confirm the gestational age — or how far along the pregnancy is — and establish an estimated due date.
- Detect the number of babies: If there is more than one fetus, the doctor should be able to see it.
- Check for ectopic pregnancy: A doctor can evaluate if the pregnancy is developing where it’s supposed to. An ectopic pregnancy is when a fertilized egg attaches outside the uterus.
- Screen for genetic orders: This exam typically includes a nuchal translucency screening, which is used to rule out Down Syndrome and physical defects of the heart like congenital heart disease.
What to expect from the second trimester ultrasound
The second ultrasound comes around 18 to 20 weeks. Also known as the “anatomy scan,” the second trimester ultrasound is administered to check on the growth of the baby’s vital organs and the position of the placenta. And yes, for those of you eager to start planning or choosing names, “fetal genitalia can also be imaged,” says Chasen.
During the second ultrasound, you can expect the doctor to:
- Examine the fetal anatomy: At this point, a doctor can detect any abnormalities in structures like the spine, heart, kidneys, brain, face, and limbs.
- Check the biological sex: If you don’t want to know the biological sex of the baby, be sure to let your health care provider know beforehand.
- The position of the placenta: A low-lying placenta, or placenta previa is when a woman’s placenta covers the cervix and can block the fetus’s path through the birth canal during labor. In this case, your obstetrician will suggest at least one additional ultrasound to see if the placenta reorients and clears the way. If it doesn’t, a cesarean delivery is required.
Additional ultrasounds may be needed
While two standard ultrasounds are considered routine, there are many reasons why an expecting parent may need more.
Some patients may have their first ultrasound prior to 11 weeks. The start of an intrauterine pregnancy is visible around 6 weeks, so an ultrasound that occurs any time after six weeks is generally reliable for determining how far along a patient may be. If you have an early ultrasound, you still will need an ultrasound at the 11 to 14 week period to properly assess development.
If any abnormalities or complications are detected during either of the routine ultrasounds, such as the position of the placenta, you might need more, says Chasen.
You may also need additional ultrasounds if your baby’s at risk of birth defects or is extremely under or overweight by the time you reach term. The following can increase your baby’s risk:
- If you smoke or drink alcohol while pregnant, or have a family history of birth defects, it can increase your baby’s risk of birth defects.
- If you have asthma, inadequate weight gain during pregnancy, or high blood pressure, it can increase your baby’s risk of being underweight.
- If you’re overweight or develop gestational diabetes during pregnancy, it can increase your baby’s risk of being overweight come delivery time.
In high-risk populations — usually due to weight, age, or medical problems — weekly ultrasounds may be recommended during the final month of pregnancy. For these patients, these quick ultrasounds are used to assess amniotic fluid and fetal movement to make sure all is well with the pregnancy.