Who’s having twins these days?
The incidence of multifetal gestations has increased significantly over the past few decades. In fact, the rate of twin pregnancies was 76 percent higher in 2009 than in 1980.
This is related to two main factors: More women are conceiving later in their reproductive lives — when spontaneous multiple pregnancies are more common — and there has been a dramatic rise in the number of couples using assisted reproductive technologies (ART) such as in vitro fertilization to achieve pregnancy.
Other factors that can raise the likelihood of conceiving twins are family history, increased maternal weight/height, race or geographical area (Nigeria has a particularly high rate of twins, and they are less common in Japan) and the number of prior pregnancies (the possibility of having twins is higher each time a mother conceives).
How does twinning happen?
Twin pregnancies can occur from two eggs being fertilized by two sperm or one embryo dividing very soon after fertilization.
In the first case, which results in fraternal, or dizygotic, twins and accounts for 70 percent of all twins, each baby has her own amniotic sac and placenta. Fraternal twins share some of the same genes, just like siblings with different birthdays.
When one embryo divides, the outcome is identical, or monozygotic, twins — the other 30 percent. Depending on when the embryo splits, monozygotic twins can have their own placentas, or they may share a placenta and, sometimes, an amniotic sac as well. Identical twins share all of the same genes. They are always the same sex and usually look very similar.
How are twins diagnosed?
Most twin pregnancies are diagnosed in the first trimester. Determination of the chorionicity (whether there are one or two placentas) and amnionicity (whether the fetuses share an amniotic sac or have their own) is a very important distinction usually made with an early ultrasound, or sonogram. Twins who share a placenta are at higher risk of pregnancy complications.
Does carrying twins pose any risks?
Regardless of the number of placentas and amniotic sacs, the risks associated with carrying twins are increased, as compared to singletons. Expectant twin mothers have a higher risk of significant nausea and vomiting in early pregnancy, diabetes and hypertension of pregnancy, as well as complications related to changes in blood volume (like anemia).
The likelihood of cesarean delivery and excessive bleeding at the time of delivery is also increased. Babies sharing the womb are more likely to have growth restriction, birth defects, stillbirth and/or to be born prematurely. In fact, women with multifetal pregnancies are six times more likely to deliver preterm.
How are twin pregnancies monitored?
Because of the increased risks associated with twin pregnancies, monitoring during pregnancy is usually more intensive. Many expectant mothers will be sent to a perinatologist — or high-risk pregnancy specialist — for consultation. Ultrasounds to monitor fetal growth and well-being are important and may be frequent depending on the chorionicity of the pregnancy.
How are twins delivered?
Most healthcare providers recommend delivery by 38 weeks of gestation, as studies show the risk of stillbirth and other fetal/maternal complications increases after that time.
The consideration for a trial of labor (attempt at vaginal delivery) or cesarean delivery is dependent on the type of twins, gestational age, positions of the babies, preference of the mother and the experience of the delivery provider. Women pregnant with twins should talk to their providers about the factors that may influence their own mode of delivery.
What will life with two newborns be like?
Many twin babies will spend some time in the special-care nursery or neonatal intensive care unit (NICU). Especially if infants are born preterm, breast milk can provide significant benefits for growing babies. Most mothers of twins are able to make enough milk to feed their babies, but a lactation specialist can be invaluable in providing help on how to schedule, position and maximize milk supply when breastfeeding twins.
While having twins can be very exciting, it can also be overwhelming to care for two infants. Ensuring that help is available when the babies come home from the hospital is important. Mothers of twins are more likely to suffer from postpartum depression, so attention to adequate sleep, regular healthy meals and good support is paramount.
Although the pregnancy and postpartum period can be difficult for moms and twins, having two babies who will inevitably have a unique and special relationship can ultimately be double the fun!
Lynsey Caldwell Owen, MD, FACOG, is an ob/gyn at Arlington Women’s Center and Virginia Hospital Center in Arlington, VA.
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