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What to Expect at Your Baby’s 13-Week Ultrasound

For expectant mothers, few things feel as exciting as learning more about their growing baby. One important tool for gaining information during your pregnancy journey is the ultrasound, an imaging technique that uses sound waves to create images (also known as sonograms) of the inside of the body. In addition to providing important information about the health and development of your baby, ultrasounds also give you your first glimpses of your new little one, which can be a powerful and moving experience! 

Healthy women usually receive two ultrasounds during their pregnancy. In this post, we’ll focus on the 13-week ultrasound, which is performed at the beginning of your second trimester. We’ll explore what to expect at this appointment, including whether you can learn the sex of your baby, and how ultrasounds work at different stages of pregnancy. 

What is a 13-week ultrasound?

As the name suggests, a 13-week ultrasound is performed during the 13 week of pregnancy, during the second trimester. During an ultrasound, the technician will apply gel to your abdomen and use a wand-like device called a transducer to transmit sound waves. Despite the cold gel, the procedure is not meant to hurt or make you uncomfortable. Now for the fun part—as sound waves bounce off your baby, images are generated on a screen that can be viewed by the technician.

This second-trimester ultrasound can give your healthcare provider a lot of important information about your baby, including its size, shape, and location in your uterus. Your doctor will monitor the baby’s growth, the amount of amniotic fluid, and the placenta position. They can also check for abnormalities of any organs or potential complications. If you didn’t have an early ultrasound at 7 or 8 weeks where your due date was confirmed, this can happen at your 13-week ultrasound instead.  

Will I learn my baby’s sex at the 13-week ultrasound?

Many expectant parents are eager to learn the sex of their baby as soon as possible and believe this to be an important part of the bonding process. If that sounds like you, you may be wondering if it’s possible to discover the gender of your baby at 13 weeks. The answer is maybe (in fact, some people call it a gender ultrasound), although you won’t be able to do so with 100% certainty.

Learning my baby’s sex

Your doctor’s ability to accurately determine your baby’s sex via ultrasound increases with how far along you are in your pregnancy. At 13 weeks, your baby’s external genitals may be visible on the ultrasound, but the images will probably not be clear enough to determine the sex of the baby with certainty. 

Some healthcare providers may make an educated guess based on what they see, while others will wait until a later ultrasound to confirm. 

If you’re interested in learning your baby’s gender, you can tell your doctor before your ultrasound and they will inform you based on the images how confident they are.

Nub theory 

While exploring when and how you will learn the sex of your baby, you may have come across something called the “nub theory”. This is a method of predicting the sex of the baby based on the angle of the genital tubercle, a small protrusion between the baby’s legs that turns into a penis in male babies and a clitoris in female babies. 

According to this theory, if the tubercle is angled upward at greater than 30 degrees compared to the spine, the baby is likely a male. If the tubercle is angled downward at less than 30 degrees, the baby is likely a female.

The genital tubercle begins to take shape between 8 and 9 weeks of gestation, so you may be able to employ the nub theory at your 13-week ultrasound. However, it’s important to note that the nub theory is not foolproof, and its accuracy can vary depending on factors such as the angle of the baby and the quality of the ultrasound images. Some healthcare providers may not use this method at all, preferring to wait for more definitive information. 

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How ultrasounds work at different stages of pregnancy

Ultrasounds serve different functions throughout your pregnancy, and they can also be performed differently. Here’s what you can expect during each trimester.

First trimester

A first-trimester ultrasound, which can be performed as early as 7 to 8 weeks after conception, is usually performed transvaginally. This means that the transducer is inserted into the vagina to get a closer look at the developing embryo. This method allows for clearer images during the early stages of pregnancy when the embryo is very small. 

The first trimester ultrasound can provide important information about your pregnancy, such as the baby’s size and location, and the presence of a heartbeat. It can also be used to confirm the due date and screen for potential complications, such as ectopic pregnancy or miscarriage. Your first ultrasound is also where you will find out if you’re having a single baby, twins, or another set of multiples. 

The first trimester is also when you can expect to receive a maternal blood test during an ultrasound. These tests measure two substances found in pregnant women’s blood: pregnancy-associated plasma protein A and human chorionic gonadotropin, which are measured to determine if the fetus is at greater risk for a birth defect or genetic disorder. 

Second trimester

The next ultrasound, occurring during the second trimester, is usually performed abdominally. This means that the transducer is placed on the outside of the abdomen, and sound waves are sent through the abdominal wall to create images of the developing fetus. This method is more comfortable for most women and allows for more detailed images of the baby.

Your second-trimester ultrasound can occur at 13 weeks,  or it can occur later in your pregnancy, around 18 to 20 weeks. At either stage, your doctor will look for any birth defects or abnormalities related to your baby’s brain, heart, bones, or kidney. This scan can usually help detect conditions such as down syndrome as well.

You may be able to determine the sex of your baby if you’re far enough along in your pregnancy and the image of your baby’s genitalia is clear. If your pregnancy is free of complications, your second-trimester ultrasound could be your last one. 

Third trimester

Many pregnant women won’t receive an ultrasound during the third trimester. But if there were any issues flagged during your previous ultrasounds, or you have medical issues such as diabetes or hypertension, your doctor will likely recommend you receive additional scans. 

Ultrasounds in the third trimester are performed the same way they are in the second, with the transducer placed on the outside of the abdomen. 

Elective ultrasounds

Outside of the medically required ultrasounds, some mothers-to-be choose to have an elective ultrasound. These are scans that are not ordered by your doctor and therefore are likely not covered by insurance. 

You might choose to have an elective ultrasound to confirm your baby’s sex, or to receive high-quality images of your growing baby that can help facilitate bonding. Some women request a 3D or 4D ultrasound, which uses advanced imaging technology to create highly detailed, three-dimensional images or videos of the baby.

However, the American Congress of Obstetricians and Gynecologists discourages getting ultrasounds for nonmedical purposes. While there are no confirmed biological effects caused by the scans, it’s possible that some could be identified in the future. 

Additionally, the Food and Drug Administration advocates for not receiving ultrasounds from people other than trained technicians, as this could lead to confusing reports and there is no guarantee the ultrasound equipment will be operated properly. Think carefully before receiving an elective ultrasound, and make sure it’s still with a trained professional like a sonographer, radiologist, or obstetrician.

Feeling nervous about your ultrasound? 

While it’s normal to feel nervous before an ultrasound, remember that as long as you’re receiving one from a professional, your health is in safe hands. Your healthcare provider will work to make you as comfortable as possible and deliver information clearly and sensitively. Do your best to balance the nerves with the excitement that comes from learning more about this new member of your family!