Twin pregnancy, all you need to know. Multiple pregnancies, twin pregnancy ultrasound.

Hey there, welcome back to another post. Today I will be talking about Twin pregnancy ultrasound, I love doing this post because to me personally I love scanning twin pregnancies, so let’s go…

As in any pregnancy, single or multiple the ultrasound protocol is the same, the first ultrasound is performed to get measurements for dating purposes , also the heartbeat should be obtained, checking the yolk sacs, amnion and Chorionicity on twins is essential to know how to proceed with the pregnancy , in case you haven’t seen I will link down below the previous post where I explained the normal protocol for the first scan.

Normal first-trimester ultrasound, scan at 6 weeks of gestation.

Well as you probably know by now being pregnant with one baby is difficult, imagine with 2 or more babies, the risks of complications on multiple pregnancies is a lot higher than single pregnancies.

If you are pregnant with twins you need to know that:

  • Morning sickness is worse due to high levels of hormones in your body.

  • Vaginal spotting and/or cramping is more common during twin pregnancies which means you will be having Ultrasounds more often.

  • Higher chances of having medical conditions like Gestational diabetes, preeclampsia etc.

  • Labor and delivery will be sooner and most likely be by C-section.

Now there are different types of twins


So below I explain the most important types of twin pregnancies seen on ultrasound, I will start with the rarest and most dangerous one which is the MONOAMNIOTIC-MONOCHORIONIC, follow by DIAMNIOTIC-DICHORIONIC, and finally, I will briefly talk about the DIAMNIOTIC-MONOCHORIONIC.

img_3014picture # 1

Ultrasound image of an Early gestation, about 7 weeks, you see the 2 fetuses inside the sac with NO membrane separation which means this is a Monoamniotic-Monochorionic twin pregnancy or Identical twins, this type of twins form after a SPLIT occurs on a fertilized egg, this type of twin shares ONE amniotic sac and ONE placenta.

img_3015Picture # 2img_30171Picture # 3

Ultrasound images on picture #2 and picture #3 are also Monoamniotic-Monochorionic but at a different gestational age,  10 weeks and 11 weeks respectively.

So because Monoamniotic-Monochorionic twin pregnancy shares ONE amniotic sac and ONE placenta, the risks associated with this pregnancy is higher than other twins, some of the risks are listed below:

  • Cord Entanglement: since there is no membrane separation between the babies their umbilical cord could get entangled, cutting off the blood supply to one of the babies.

  • Cord compression: As they share the same sac they might press against the others umbilical cord while making internal movements. Prolonged pressure may cut off blood supply and nutrients to one of the babies resulting in fetal death or weight discrepancies.

  • Twin to Twin Transfusion Syndrome: This syndrome happens when one of the twins receives the majority of the nourishment in the womb, causing the other twin to be undernourished. That is detected on regular scanning based on the physical development of both babies.

  • Preterm labor: always occurs on mono-mono twins due to the high risks on cord entanglement and compression, is usually done by C-section between 34 to 36 weeks, however, some mono-mono can be delivered at 26 weeks if there are other complications.

Other facts about Mono-Mono twin pregnancies:

  • Mono-Mono babies are always the same gender since they originate from the same fertilized egg.

  • Mono-Mono twins are rare, ONLY 1% of twins are mono-mono.

Now let’s talk about DIAMNIOTIC-DICHORIONIC.

img_30131Diamniotic-Dichorionic at 7 weeks.

img_3011Diamniotic-Dichorionic at 9 weeks.

img_3012Diamniotic-Dichorionic at 11 weeks.

The last 3 ultrasound images are Diamniotic-Dichorionic twin pregnancies, This type of  twins can be Monozygotic or Dizygotic which means that can occurs after 2 different eggs are fertilized by 2 different sperms or ONE fertilized egg DIVIDES into 2 blastocysts and Reaches the uterus and is implanted, this type is the most common type of twins about 72 to 80% of all cases.

Complications of Diamniotic-Dichorionic twins:
While the complication rate is still much higher with twins than with a singleton pregnancy, a Diamniotic-Dichorionic pregnancy carries the lowest rate of complications amongst twin pregnancies however some of the complications can include:

*Increased risk of intrauterine growth restriction (IUGR): Means that one baby is not growing appropriately compared to the other twin.
*Placental related problems such as increased risk of velamentous cord insertion, marginal cord insertion or placenta previa.


This type of twins is about 20% of all twins, forms after ONE single fertilized egg SPLITS, this type of twin shares ONE placenta but have 2 different Amniotic sacs.

img_3029Ultrasound image that shows SINGLE SHARED placenta seen on the bottom of the picture, clear membrane separation between the babies is seen in the middle.

img_3030Ultrasound image of a mono-di twin pregnancy again showing a SINGLE SHARED placenta that is located on the left side of the picture, you can see also the membrane in the middle of the babies.

So remember that this type of twin shares ONE placenta, so there are complications associated with it:

Potential complications that can occur with this type of pregnancy include:
problems related to abnormal placental vascular anastomoses
*twin to twin transfusion syndrome.
*twin embolization syndrome
*twin reversed arterial perfusion sequence.
*demise of one twin: often associated with some adverse outcome to the other twin.
*Other placental insertion related problems such as increased incidence of velamentous cord insertion and/or increased incidence of marginal cord insertion.

Other types of multiple pregnancies can also occur (Triplets, quadruplets etc.)  the most important purpose of the Ultrasound is identify Chorionicity, one placenta vs two placentas can make the world of the difference.

The ultrasound protocols are always the same for any type of pregnancy.

And remember that being able to grow inside your body one life is precious but being able to grow more than one life at a time is even more precious, as I called it ” the miracle of life”, you are blessed and every baby is a blessing.

OK so this is the most relevant info about TWINS, I will start the weekly scanning on my next post, from week 7 to week 40 of pregnancy with ultrasounds, as usual, see you on my next post.

XO zadi.

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Hi, welcome to my site, I am Zadi, ultrasound tech and mom of 2 boys. Being a mother is one of the most beautiful things that have happened to me, but motherhood can be frustrating and difficult sometimes. I am sure any mom can relate to this. With this blog, I want to help you navigate the stages of pregnancy and parenting gracefully, by sharing my medical knowledge and my experience as a mom with you.

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