Between 11 and 13 weeks, it is very likely you will be sent for an ultrasound. The 12 week ultrasound is usually a lot of fun for the parents since babies tend to be active and photogenic. Parents are almost always in awe that the baby is already fully formed and there is a lot of kicking, jumping, and waving going on, even though the mother can’t feel it yet. By 12 weeks, the brain and other organs still need to grow and mature, but the baby is completely recognizable as a human with all the parts in place; skull, head, arms, legs, fingers, toes, liver, heart, stomach, bladder etc. Even though everything is there, it is tiny so a full in-depth analysis of all the organs and body parts will still need to be done at 18 to 20 weeks. Click here for more information on the 18 to 20 week ultrasound.
The baby’s anatomy will be briefly examined but the main purpose of the 12 week ultrasound is to take a measurement of the Nuchal Translucency or NT. The NT is a small collection of fluid that lies just under the skin at the back of the baby’s neck. This is usually well visualized with ultrasound and is measured to the nearest 100th of a centimeter. In order to do this test, sonographers and doctors need to be specially trained and certified. If it is thickened, that can indicate that the baby might have Down’s Syndrome or another chromosomal abnormality. It is not fully understood why the NT thickens in these babies, but it is probable that it is due to aberrations in development of the lymphatic system and tissues in chromosomally abnormal babies. However, plenty of babies with thickened NT’s are perfectly normal so DO NOT PANIC if your baby is found to have a thickened NT! However, it does mean that you will be offered further investigation with amniocentesisor CVS (click for more information), as well as additional monitoring as the pregnancy progresses.
The cutoff for normal NT thickness is generally 3 mm. If it is thicker than that, there is cause for concern, But again, most of the time, the good news is that most babies with a mildly thickened NT will be found with further testing to have normal chromosomes! But these babies are not out of the woods yet—some of these babies have a thickened NT because of a heart defect, cystic neck mass, or other anatomical problems. You will need follow up with serial ultrasounds and a targeted ultrasound of the fetal heart (a fetal echocardiography) to be sure that there is nothing else to be concerned about.
NT and First Trimester Screening: The NT measurement is taken to the nearest 100th of a centimeter. This number is sent to the lab performing the First Trimester Screening along with an ultrasound measurement of the length of the baby from crown to rump (which confirms the age of the fetus). Using sophisticated multivariate statistical formulas, the lab crunches the value of the NT measurement along with some values from a blood sample from the mother and her age at delivery to arrive at a risk estimate of Down’s or other common chromosomal problems. For more information on First Trimester Screening, click here.
Can you tell the gender at this scan? Boys and girls both have external genitalia at this point so it is not easy to tell gender yet. Every once in a while, by looking at the direction that the external phallus lies, the doctor or sonographer may feel confident enough to make a prediction. Don’t get too excited and buy blue clothes or paint the room pink yet!!! Predicting sex at this point is fraught with risk and many times, families are told what they thought was a boy turns out to be a girl (or vise versa) at the 18 to 20 week scan. You CAN tell the gender with near-perfection at the later scan. 12 weeks is just a bit too early to be sure. For more on gender determination, click here.
Can I get 3D/4D ultrasound at 12 weeks? 3D and 4D (4D is just 3D over time—see 3D/4D for more information) can be done at any point in a pregnancy and it can be really amazing at 12 weeks. But, because it is still a fetus and not a cute, chubby baby yet, it can look like a grasshopper or alien. Remember that 3D and 4D are computer generated images and while they can be fun, they shouldn’t be taken too literally.
If I refuse the screening for Down’s syndrome, do I still need a 12 week ultrasound? Of course, all testing and screening tests are optional. Many times, your doctor or midwife will encourage you to have the 12 week scan whether or not you decide to do the First Trimester Screening (see First Trimester Screening) since a thickened NT can also signal that there could be some anatomical defects present, especially with the heart. Studies repeatedly show that IF cardiac and other defects are found before birth, good outcomes are more likely. Babies with problems can be delivered at specialty centers with a team of doctors and professionals ready and prepared to provide the necessary support to maximize survival rates and successful corrections.