Your Pregnancy Matters
How we diagnose birth defects
January 27, 2015
It’s by far the No. 1 question we get from patients – “Is my baby OK?”
We take several steps in answering this question. Most babies will be born without any problems, but between 3 and 5 percent of all babies will be born with a birth defect. Some people are surprised birth defects are that common.
Also, doctors today can diagnose some birth defects — up to 70 percent of them by some estimates — before the baby is born.
Questions we ask
Diagnosing birth defects involves questions and tests. First, to determine if the baby could be at risk for a birth defect, we ask about three things:
- The patient’s family medical history
- The patient’s personal medical history (including previous pregnancy outcomes)
- Medications the patient has taken
The answers guide our analysis of test results. Some birth defects, such as spina bifida, have a hereditary factor. If that condition runs in the family, we pay extra attention to the baby’s spine during the ultrasound.
Family medical history is also important because gene mutations can cause certain birth defects.
The patient’s personal medical history also plays a big role. If the mother has diabetes when she becomes pregnant, for example, her baby may be at an increased risk for spina bifida or heart-related defects.
Obviously, our concern is heightened, too, if we learn the mother previously had a child born with birth defects.
We also ask the patient about any medications she has taken. Certain medications are linked to an increased risk of birth defects. With use of any medication during pregnancy, it’s our job to balance the risk it may present to the baby with the benefit it provides to the mother.
Tests that help identify birth defects
After the questions, doctors routinely use blood tests and ultrasounds to actually diagnose birth defects.
For example, during the second trimester, a blood sample from the mother is analyzed to measure alpha-fetoprotein levels. This protein is produced by the liver of the baby during pregnancy. Any time there is a break in the fetal skin, the amniotic fluid (and then eventually the mother’s blood) will contain higher levels of this protein.
High levels of alpha-fetoprotein in the maternal blood can indicate birth defects such as spina bifida (where the closure of the spinal cord has been interrupted) or gastroschisis (where intestines are developing outside the abdominal wall).
Ultrasound is the most common tool used to detect birth defects. Doctors use an ultrasound to conduct a system-by-system analysis of the baby. Ultrasounds are usually performed when the mother is 18- to 20-weeks pregnant but can be done earlier. Various parts of the baby are examined, including the brain, heart, and spine.
Doctors take measurements to make sure the baby is growing normally. If any of the measurements are abnormal, it can lead to the diagnosis of a birth defect.
Other specialized testing may be ordered to help with the diagnosis of birth defects. A detailed examination of the baby’s heart, called a fetal echocardiogram, may be performed by Maternal-Fetal Medicine specialists or by Pediatric Cardiologists. Fetal magnetic resonance imaging (MRI) may also be helpful to further understand abnormal developments of the baby’s brain or when ultrasonography is difficult because there isn’t very much fluid around the baby.
Most common birth defects
One of the most common birth defects – affecting about 1 out of 100 pregnancies – involves a part of the baby that is mostly outside its body. It happens when the umbilical cord has two blood vessels instead of three. It does warrant a careful, detailed look at other structures in the fetus, but unlike some of the other birth defects I’ve mentioned, this is usually not concerning as long it’s the only abnormality.
Congenital heart defects are not uncommon. It’s hard to predict them because we frequently see small holes inside the heart when an ultrasound is performed. Often these holes disappear by the time the baby is born.
Other relatively common birth defects include:
- Spina bifida
- Club feet
- Cleft lip
- Kidney defects
What are the options?
When a birth defect is detected in an unborn baby, we have a discussion with the parents about the options available to them. Those options depend on the type of birth defect diagnosed.
Doctors can repair some birth defects, including spina bifida, while the baby is still inside the uterus. A study published in 2011 found that repairing spina bifida before the baby is born produced better outcomes than surgery performed after birth.
Some bladder obstructions also can be treated while the baby is still in the uterus.
But many other birth defects cannot be repaired before the baby is born. Some parents opt to terminate the pregnancy, and others choose to continue the pregnancy.
In any scenario, our goal to help parents understand what we are seeing on a prenatal ultrasound, what kind of problems we anticipate the baby may have after birth, and what options they have for managing the pregnancy.