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Prenatal Care for a Multiple Pregnancy

Learning you are expecting twins, triplets or higher-order multiples can be exciting but also overwhelming. A multiple pregnancy is different than a singleton pregnancy in a variety of ways.

Families at the Brigham's Comprehensive Care Center for Multiples often have questions about keeping mom and babies healthy, possible complications during pregnancy and delivery, what additional testing is needed and much more. Our experts are here with answers to keep you well-informed throughout your pregnancy.

Both Doctor and Nurses are always so informative and a pleasure to speak to. I know I’m not the only patient, but they sure make me feel special to be carrying twins. They ease my nerves. They always make me feel comfortable and joyful when I leave my appointment. I cannot wait for them to deliver my two healthy baby boys.” - Tania, patient

Prenatal Screening and Diagnosis

Any woman carrying more than one baby should receive routine aneuploidy screening. This assessment reveals whether a fetus is at higher risk of having an abnormal number of chromosomes — as in the case of Down syndrome.

Because you are carrying more than one baby, genetic screening options and interpretation of the results are slightly different and require medical expertise. Every patient at the Center for Multiples meets with a genetic counselor who specializes in multiple gestations. After meeting with one of our genetic counselors, you will have all the information needed to proceed with the best genetic screening options or diagnostic tests for your multiple pregnancy.

We employ common diagnostic tests such as:

  • Chorionic villus sampling (CVS) identifies certain genetic conditions using sample cells from the placenta(s). It's usually performed at 10 to 13 weeks.
  • Amniocentesis identifies certain genetic conditions using a sample of the amniotic fluid. It's usually done after 15 weeks.
  • Ultrasound is a type of technology that produces images of a fetus within the womb and is used to monitor the fetus' anatomy and development. Learn more below.

Types of Twins and Triplets

When you have a twin pregnancy, your prenatal care (prenatal visits and ultrasound) will be based in part on the type of twins you are carrying. In general, this refers to whether the twins each have their own placenta, share one placenta or share one placenta and one amniotic sac.

Fraternal (dizygotic) twins are conceived when two separate eggs are fertilized and implanted in the uterus at the same time. The twins have different genetic makeups and may or may not be the same gender. All fraternal twins are dichorionic-diamniotic (Di-Di) twins.

Identical (monozygotic) twins are conceived when one egg becomes fertilized and then splits into two separate embryos. They are the same gender and have the same or nearly the same genetic makeup. They may not be exactly identical because some genes are expressed differently.

Classification of Twins

Monozygotic twins are classified as follows:

  • Monochorionic diamniotic (Mo-Di) twins separate into two embryos four to eight days after fertilization. The twins share a placenta, but each has its own amniotic sac.
  • Monochorionic monoamniotic (Mo-Mo) twins separate eight to 13 days after fertilization. They share the same placenta and amniotic sac.
  • Conjoined twins separate 13 to 15 days after fertilization. They share the same placenta and amniotic sac as well as some organs.

Classification of Triplets

Triplets are classified as follows:

  • Trichorionic-triamniotic (Tri-Tri) triplets: Each triplet has its own placenta and amniotic sac.
  • Dichorionic-triamniotic (Di-Tri) triplets: Two of the triplets share a placenta, with separate amniotic sac, and the third triplet has its own placenta and amniotic sac.
  • Mochorionic-triamniotic (Mo-Tri) triplets: All triplets share one placenta, and each has its own amniotic sac.

In rare cases, two of the triplets can also share the placenta and amniotic sac.

Triplet pregnancies are at a higher risk of complications related to preterm birth. On average, triplets are delivered around 32 weeks. A consultation with a maternal-fetal medicine (MFM) specialist is recommended to review potential risks and pregnancy outcomes.

Ultrasounds

During a multiple pregnancy, more frequent ultrasounds are necessary to monitor the babies' growth rates and any possible complications.

Below are our general guidelines for ultrasounds during a multiple pregnancy. Please keep in mind that the schedule may differ depending on your particular circumstances.

Purpose of Ultrasound

Timing

Additional Notes

Determining date of pregnancy and type of twins or triplets

Optimal at 7–10 weeks

Measure twins or triplets (often referred to as the "crown-rump length").

Conducting aneuploidy screening

10–13 weeks

Assess each baby's nuchal translucency measurement and early anatomic structures. (Nuchal translucency screening uses an ultrasound test to check the area at the back of the fetal neck for extra fluid.)

Scanning anatomy for all multiples

Optimal at 18–20 weeks

Assess for structural abnormalities.

Follow-up for uncomplicated Di-Di twins

Starting at week 24

Assess fetal growth every 4 weeks.

Follow-up for uncomplicated Mo-Di and Mo-Mo twins*

Starting at week 16

Assess:

  • Bladder and amniotic fluid volumes every 2 weeks
  • Growth every 2–4 weeks

Follow-up for uncomplicated Tri-Tri triplets

Starting at week 24

Assess for fetal growth every 2–4 weeks

* Uncomplicated Mo-Mo twins follow a similar ultrasound schedule as uncomplicated Mo-Di twins until admission to the hospital for inpatient daily fetal testing around 24–28 weeks.

Seeing a Maternal-Fetal Medicine Specialist

The Center for Multiples is part of the Division of Maternal-Fetal Medicine, which offers the most advanced maternity care available today. Care is provided by MFM specialists, who bring expertise in managing the challenges and complications of high-risk pregnancies. Please note that not all twin pregnancies are considered high-risk pregnancies.

If you develop medical complications related to your health or the health of your babies, a consultation with a MFM specialist may be recommended. If you receive your prenatal care at a practice outside of the Brigham, you can have a consultation with one of our MFM specialists and retain your local obstetrician.”

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