Multifetal gestation: Clinical sciences

Multifetal gestation is any pregnancy in which more than one fetus is present. This includes twin, triplet, and other higher order pregnancies. Multifetal gestations carry increased maternal risks, including diabetes and preeclampsia, as well as increased fetal risks, such as preterm birth and intrauterine fetal demise, also known as IUFD. The amnionicity, meaning the number of amniotic sacs, and the chorionicity, meaning the number of placentas, influence the degree of risk for the pregnancy.

When a patient presents with a suspected multifetal gestation, your first step is to obtain a focused history and physical examination. Patients may report significant nausea and vomiting, or hyperemesis; which is due to the increased beta human chorionic gonadotropin levels that occur with multifetal gestations. They may also have certain risk factors for a multifetal gestation such as assisted reproductive technology, like in vitro fertilization or ovulation induction; or increased maternal age or parity. On a physical exam, you may notice the uterine size is greater than expected based on your patient’s last menstrual period.

Next, order an obstetric ultrasound, which will be most accurate when performed at the end of the first trimester or early second trimester. The ultrasound allows you to assess the number of fetuses, the chorionicity, and the amnionicity, which will guide the management of the pregnancy. This is also a good time to consult the maternal-fetal medicine team for their involvement in your patient’s care!

If the obstetric ultrasound demonstrates two fetuses, then you know this is a twin pregnancy. Next, look for the twin peak sign, also known as the lambda sign, which looks like a triangular wedge of placental tissue extending at the base of the intertwin membrane. If this is present, then you know there are two placentas and each fetus is separated by a thick membrane; so your diagnosis is a dichorionic diamniotic twin pregnancy!

Now, standard care for all patients with a multifetal gestation include counseling on appropriate weight gain and nutritional needs. This includes increased amounts of folic acid and other micronutrients to ensure there’s enough available for multiple fetuses to develop. Because of the increased risk of preeclampsia, order low-dose aspirin to start between 12 and 28 weeks of gestation. Next, offer fetal aneuploidy screening, and be sure to cover some specific points with your patient. For example, explain that while aneuploidy screenings, like cell-free DNA testing or the quad screen, can be used for multiples, caution your patient that this testing can be less accurate with a multiple gestation, and it cannot determine which fetus might be affected.

Also let them know that nuchal translucency, which is an ultrasound that looks at the thickness of the back of the fetal neck, is the only non-invasive option that separately evaluates each fetus. Additionally, explain that diagnostic testing, such as chorionic villus sampling or amniocentesis, usually provide information on each fetus; but keep in mind these are invasive tests, and counsel your patient on risks and benefits. Next, since multifetal gestations are at increased risk of developing structural anomalies, perform an extended fetal anatomic survey. And finally, start antenatal fetal surveillance at 36 weeks of gestation because of an increased risk of IUFD.

Okay, let’s go over some specific care needed for dichorionic diamniotic twin pregnancies. Starting at 20 weeks, complete serial ultrasounds every 3 to 4 weeks to evaluate for fetal growth restriction, which will provide information for counseling on the mode of delivery. A trial of labor is often possible if certain criteria are met, such as when both twins have a cephalic presentation. You could also attempt a trial of labor if the presenting twin has a cephalic presentation and the second twin is not cephalic.

In this case, you can consider attempting a breech extraction, as long as the second twin isn’t estimated to be more than 20 percent larger than the first. It’s also reasonable to perform a C-section for a twin gestation if you’re not experienced with breech extractions or for patient preference. With uncomplicated dichorionic diamniotic twin pregnancies, delivery should occur between 38 weeks 0 days of gestation and 38 weeks 6 days of gestation, though it’s common to deliver earlier if medically indicated.