Week-by-Week Guide to Twin Pregnancy: What to Expect

Depending on who you ask, you might hear that being pregnant with twins is a unique experience. But the truth is that every pregnancy is singular—and in many twin pregnancies, the only major difference is the amount of prenatal care you’ll receive (hint: it’s more).

Babies tend to follow the same developmental pattern until around the 26th week, with the exception of some monochorionic twins. Twins who share a single placenta and amniotic sac may be subject to more developmental complications, which can change the course of a typical fetal timeline.

No matter what types of twins you’re carrying, it doesn’t hurt to have an idea of what to expect from the journey. Here, we’ll provide a look at your twin pregnancy symptoms by week and signs of a twin pregnancy to give you a better idea of distinguishing features and some symptoms you might experience.

What’s the difference between twin pregnancies and singleton pregnancies?

Where there is only one type of singleton pregnancy, multiple gestation can be divided into three categories:

• Fraternal twins – Fraternal twins originate with two separate eggs and two separate sperm. In your uterus, they have their own placentas and amniotic sacs. This is one of the safest twin pregnancies to have, as each baby will be cushioned by their own sac and receive their own source of nourishment in utero.
• Identical twins – Identical twins or monochorionic twins yield from a single egg that’s split in two. Do identical twins have the same DNA? Yes, they do. This type of pregnancy can result in two distinct types of pregnancies:
  • Monochorionic-diamniotic twins – Single placenta, two amniotic sacs
  • Monochorionic-monoamniotic twins  – Single placenta, single amniotic sac

Identical twin pregnancies receive a higher degree of care and monitoring to ensure each twin is growing well—but any kind of twin pregnancy will require a more rigorous prenatal care plan than a single pregnancy.

Even still, many providers don’t ramp up prenatal appointments until the end of the second trimester, when fetal complications are more likely to crop up. One of the main concerns for twin pregnancies is preterm labor. To be cautious, many moms elect to switch their prenatal provider to someone who specializes in twin pregnancies and the potential risks that come with them.

Twins Timeline: First Trimester

Most expecting moms find out they’re having twins during their first-trimester ultrasound. Early ultrasounds are usually held between 6 and 8 weeks of pregnancy, while dating ultrasounds happen around the 10-week mark. It’s worth noting that having twins does not typically cause a false negative pregnancy test. Pregnancy tests are designed to detect the hormone hCG produced by the developing placenta. If you are carrying twins, the hormone levels are often higher, making it more likely for the pregnancy test to confirm the pregnancy accurately.

So, if you’re curious about whether can twins cause false negative pregnancy test results, rest assured that the reliability of pregnancy tests is generally not affected by the number of embryos. The ultrasound, conducted later in the first trimester, remains the primary method for confirming multiple pregnancies.

Depending on when your first scan takes place, your babies may have already passed several of the following milestones:

• Week 6 (4 weeks after conception) – Though it’s still too early to take their weights, at week 6, the first inklings of your embryos’ heartbeats can be heard! Their legs, skulls, and umbilical cords are also growing.
• Week 8 – Two weeks later, your fetuses have left the embryo stage. Along with their hearts, they’ve begun forming the beams of their nervous system (the brain, nerves, and spinal cord), as well as their lungs.
• Week 11 – Halfway through your first trimester, your babies are starting to develop definitive facial features. They’re also quickly growing their ears, eyes, arms, and legs—the last of which you may feel next week when many begin to kick.

When it comes to symptoms of twin pregnancy week by week, most expecting moms deal with the same symptoms they do for singletons, like morning sickness, fatigue, and a near-constant urge to use the bathroom. However, there are some reports of exaggerated twin pregnancy symptoms, such as:

• Heightened morning sickness
• A more rapid weight gain (this will ramp up in your second trimester)
• Extra activity in your belly (four legs tend to flutter more than two!)
• A subtle, intuitive awareness that you’re having multiple babies before your doctor confirms it

Many multiple pregnancies exhibit higher-than-average levels of human chorionic gonadotropin (hCG) in the bloodwork confirming a pregnancy. You may also be tipped off to your twins based on some life circumstances, which can make having multiples more probable:

• Being over the age of 35 – Older women tend to release more eggs when they ovulate.
• Genetics – If twins run in your family, you’ll be more likely to have them.
• Using assisted reproductive technology (ART) – Fertility treatment like in vitro fertilization (IVF) raise the likelihood of carrying twins.
• Having obesity – Women with a body mass index (BMI) above 30 are likelier than others to have twins.

No matter when you discover you’re having twins, your first trimester will likely be a gradual ramp-up to the unique characteristics of a twin pregnancy.

Twins Timeline: Second Trimester

Week 13 marks the beginning of your second trimester. During this period, you’ll probably start to notice your growing belly rather quickly (twin moms often notice they start to “show” earlier than their singleton mom peers).

Inside your uterus, your twins are steadily sizing up to their future selves, racing towards the 1oz. mark. Their crucial organs like those within the urinary and reproductive systems are beginning to take form. Their fingers are also developed enough for them to start sucking their thumbs!

Let’s take a look at what else is ahead for the second trimester:

• Week 14 – The formation of your twins’ sex organs is underway. Another crucial development is their ossification, where their skeletal system is beginning to change from soft to hard. To accommodate your babies’ rapid growth, you might notice your appetite has gotten a boost and that your belly is beginning to grow.
• Week 18 – For twin pregnancies, week 18 marks the middle of your pregnancy (most twin births take place at 36 weeks—earlier than singleton pregnancies). At this stage, much of the changes your babies are experiencing are internal: they’re becoming more aware of senses like sound and may even hear the sound of your heartbeat.
• Week 20 – As your babies grow, they’re developing fatty deposits and a form of downy hair known as lanugo. They also tend to become more active at this stage, and you may begin to feel the brunt of their kicks (and plenty of activity until your due date).

Week 20 is a critical milestone, as your growing twins are beginning to absorb most of the space available in your uterus. Your care team may begin monitoring their progress more aggressively to ensure they have enough space to grow.

It’s also best to start seeing your provider more frequently to scan for several complications that can crop up at this stage, such as:

• Selective intrauterine growth restriction (sIUGB) – This complication occurs when one twin is growing at a more rapid rate than the other. This may be caused by a dysfunctional umbilical cord or a developmental complication in one fetus.
• Preeclampsia – About 9.5% of twin pregnancies coincide with preeclampsia, which tends to set in earlier and with a higher incidence than singleton pregnancies. Preeclampsia causes hypertension (high blood pressure) and excessive levels of protein in urine. It can compromise babies’ abilities to receive nourishment, and it’s usually treated best through preventative measures.

Twins Timeline: Third Trimester

The third trimester is when many twin moms’ experiences diverge. If babies are in optimal health, they’ll continue refining in development: accumulating fat, peeping open their eyes in response to light, and starting to resemble who they’ll look like when they arrive.

As all this is happening, the unique risks associated with twin pregnancies are being carefully monitored. Twin moms stop by their provider for a prenatal visit once per week at this stage. With that, there are several areas providers will pay close attention to support your babies’ growth and birth:

• Weight gain – Twin moms tend to gain between 37 and 54 lbs. during their pregnancy (singleton moms put on about 30). You will likely continue to gain weight in the third trimester, which helps reduce the risk of low birth weight for your babies. Some estimates recommend gaining around 1.5 lbs. per week for optimal fetal and maternal health.
• Signs of preterm labor – One of the biggest concerns for your care team is early signs of preterm labor, which can sometimes arise at the end of the second trimester. The majority of twin pregnancies are delivered between 32 and 38 weeks. A full-term twin pregnancy is considered 37 weeks. You can expect due changes once you experience signs of preterm labor:
  • Dull pain in the lower back
  • Cramping and pressure around the pelvic floor or lower abdomen
  • Vaginal discharge
  • Spotting or light bleeding
  • Contractions (a regular tightening and relaxation in the abdomen)

Looking ahead to your due date, it’s important to be aware that delivering twins is always more complicated than delivering one baby. For example, for a vaginal birth, the first baby must be in the anterior position, with their head facing down. Cesarean births are very common for twin and multiple pregnancy, and they’re usually recommended if you’ve experienced any complications along the way.

Discover Your Baby’s Gender Early with SneakPeek

From conception to their due date and beyond, carrying twins can be a handful—but the more closely you communicate with your care team, the more confident you’ll feel in navigating the complexities of the journey.

Did you know that you can get a DNA test while pregnant? Become even more informed about who’s on the other side of your pregnancy with SneakPeek’s Early Gender DNA Test. With this at-home gender blood test, you’ll discover your baby’s gender as soon as 6 weeks into your pregnancy with over 99% clinically proven accuracy and DNA-based results.

SneakPeek moms can take their Sneak Peek test at home, mail their sample to the SneakPeek labs, and receive triple-reviewed results on the same day the labs receive them. We’ll even send you a complimentary downloadable report you can share with your provider to review. Visit us today to join the 1 million+ moms who’ve gotten to know their babies earlier with SneakPeek.

This post has been reviewed for accuracy by:

Priscilla Jeng

Priscilla Jeng is an accomplished digital marketing expert, currently leading as the Associate Director of Digital Marketing at Gateway Genomics, the parent company of SneakPeek. With over four years at Gateway Genomics, Priscilla has played a pivotal role in amplifying the company's mission to develop innovative genetic tests. Her proficiency in digital marketing and her comprehensive understanding of the genomics industry position her as a key contributor to SneakPeek's marketing endeavors.

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