Most parents probably already know how important and useful an ultrasound scan is, particularly around 5 months into the pregnancy, in order to check the development of the baby. An ultrasound then can check on structures that are important for the baby’s development, such as the spine and internal organs. But, did you know that an ultrasound in the early stages of pregnancy is important and useful too? What is the benefit of an ultrasound scan in the first trimester? Today, our doctor will answer this question.
- First, an ultrasound can be used within the first trimester to confirm a viable intrauterine pregnancy. The ultrasound is used to check that the embryo is developing inside the womb (rather than inside a fallopian tube, for example), to confirm that the embryo has been fertilized (rather than a blighted ovum), and to confirm that the baby has a heartbeat.
- Second, an ultrasound can be used within the first trimester to accurately date the pregnancy. The ultrasound is used to calculate the exact gestational age by measuring the length of the baby. Measurements during this period will have only small errors. As such, using this method to date the pregnancy is more accurate than basing it on the last menstrual cycle, because ovulation doesn’t always occur at precisely the same time in each cycle. Having an accurate estimate of the gestational age of the baby is very important for further pregnancy planning, whether that is screening for chromosomal abnormalities, assessing fetal growth, or determining the correct due date, which is helpful in making sure the baby isn’t born too early or too late, as well as scheduling an appropriate delivery date in case of complications.
- We can also use an ultrasound to know whether it’s twins or not. An ultrasound can be used in the first trimester to confirm the number of babies. This is especially important for mothers who used fertility drugs or IVF methods. An early pregnancy ultrasound can also determine the type of multiple pregnancy (called chorionicity). Knowing this information is necessary for appropriate care throughout the pregnancy, and a delayed assessment could hinder treatment decisions.
- We can use an ultrasound for early diagnosis of some major fetal abnormalities during the first trimester, such as abnormalities in the skull or spine, abdominal wall defects, some major congenital heart defects, abnormalities in the number or appearance of limbs, fetal edema, or certain chromosomal abnormalities.
- We can measure the thickness of the nuchal translucency (NT). The NT refers to the pocket of fluid at the back of the fetal neck. The NT can be measured in babies with a length between 48 and 84 mm, or approximately 11-14 weeks into the pregnancy. This test is important and very accurate at detecting chromosomal abnormalities, in particular Down syndrome (trisomy 21), Turner syndrome (45,X0), and even some other genetic disorders and congenital heart diseases.
- We can check the blood flow resistance in blood vessels that supply the uterus. This is useful to predict pre-eclampsia and fetal growth restriction.
- We can also use ultrasound to evaluate the mother’s pelvic cavity to detect preexisting conditions, such as uterine fibroids or ovarian tumors. This check needs to be done early in the pregnancy because these conditions are more difficult to detect or assess later in the pregnancy and because they can have a significant effect on the progression of the pregnancy. Some conditions may even require surgery.
Based on all of this, parents can see that an ultrasound scan in the first three months of pregnancy is very important. Therefore, our doctors recommend that mothers come for prenatal care in the first trimester and have an ultrasound scan during this time.
Assistant Professor Mr. Kiattisak Kongwattanakul, M.D.
Obstetrician and gynecologist specializing in maternal and fetal medicine
Obstetrician and gynecologist specializing in maternal and fetal medicine
