Welcome to the second trimester! One down, two to go. Over the next few months, your babies will undergo significant changes. Their tiny organs will continue to develop and grow, and they’ll gain the ability to hear and swallow. You’ll also begin to feel your little ones moving around in your belly! Let’s talk about 13 weeks pregnant with multiples.
Many pregnant people report they feel their best during the second trimester. Take a look at what your babies are up to this week, and what you can expect over the next few months.
What’s going on with your babies?
Your little ones are doing big things behind the scenes! They now weigh about 0.8 ounces and are close to 3 inches long. For a size reference, think of a lemon… or, should we say, multiple lemons.
Your babies have also begun forming their fingerprints. Fun fact: even if your multiples are identical, they will each have their own unique set of prints. Your babies’ organs and veins are now visible through their skin, which remains translucent.
During the first trimester, your healthcare provider would have determined whether you are expecting identical or fraternal multiples — or even a combination of both if you’re carrying more than two babies. This trimester, you’ll be able to see the sex of your babies on an ultrasound if you wish to know.
How are you feeling?
Hopefully, quite a bit better! The second trimester is when most pregnant people feel their morning sickness begin to subside, but it’s normal for it to carry on a bit longer in some cases. If you’re still feeling less than stellar, brighter days should be on the horizon soon.
You’ve also had some time to sit with the news of multiples for a bit, so you may be feeling less shocked and more confident about welcoming more than one baby. Many people feel comfortable announcing their pregnancies in the second trimester, but how and when you share the news is a personal decision.
Will testing take place this trimester?
If you haven’t already had a genetic screening test, there’s still time. The Non-Invasive Prenatal Screening test (NIPS or NIPT) can be done anytime after 10 weeks of pregnancy. The screening can identify if one or both of your babies are at risk of a genetic condition. It’s important to know that this cannot distinguish between your babies. So if it does indicate risk, it could be that only one of your babies is affected, or it could be that all are…or in rare cases, it could be a false positive. Talking with your provider and a genetic counselor can help you determine if confirmatory, more invasive testing is a good idea for you.
This is the last week of pregnancy for a CVS or chorionic villus sampling. This is an invasive test that can diagnose genetic conditions. A sample of each of the babies’ placentas is taken and tested. It does come with some risk. And, like any test in pregnancy, it isn’t 100% accurate. But it is more accurate than screening tests.
Additional tests in the second trimester
Maternal Serum Alpha-FetoProtein (msAFP)
This is a blood test that can be done between weeks 15 and 22. It tests for the presence of a protein produced within the babies’ bodies. If it is in your blood at higher levels than expected, this can indicate that one or both babies could have a birth defect involving their spine or belly. While this is commonly something identified by ultrasound, ultrasound isn’t 100% accurate in identifying these things. So the blood test is another way to avoid missing a potential diagnosis before the babies are born.
Ultrasound
Chances are, you’ve already had at least one ultrasound during your pregnancy. Between weeks 18 and 20, you will have an anatomy ultrasound to examine your babies more closely. It will examine the placenta(s), fluid levels around the babies, and all of the babies’ organs and body parts. Because a multiple pregnancy has a higher risk for complications, you may have more than one ultrasound in the second trimester.
Anemia Screening
At the same time as your glucose test, a complete blood count is typically done to identify potential issues. The most common being anemia, or a low number of red blood cells. This is common in pregnancy, and if significant enough, you may benefit from iron supplements for the remainder of pregnancy. Your provider can tell you if this is necessary in your case.
Glucose screening
Gestational diabetes can cause complications for your and/or your babies’ health during and after pregnancy if untreated. So, it is important to identify if you have it or not! This is typically tested for between 24 and 28 weeks, though it may be done earlier in pregnancy if you have certain risk factors. To take the test, you will first drink a sugary liquid, similar to flat soda; your blood will then be drawn to test your glucose levels. If your result is elevated, you may have to go on to a three-hour glucose test. If diagnosed with gestational diabetes, your provider will connect you with education and resources so you can learn how to manage your blood sugar until your babies are born.
Reviewed by the Ovia Health Clinical Team
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Sources
- American College of Obstetricians and Gynecologists. “Multifetal gestation: Twin, triplet, and higher order multifetal pregnancies.” National Guideline Clearinghouse. U.S. Department of Health and Human Services, May 2014. Retrieved May 15 2021.
- Mayo Clinic Staff. “Twin pregnancy: What multiples mean for mom.” Mayo Clinic. Mayo Clinic, Updated December 17 2024. https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/twin-pregnancy/art-20048161.
- “FAQ: Multiple pregnancy.” American College of Obstetricians and Gynecologists. American College of Obstetricians and Gynecologists, July 2015. Last reviewed: May 2025.
