Tragically, just like some singleton babies are lost in the second or even third trimesters, the same goes for twins. But the risks to the mother and surviving baby are much greater in the case of a multiple pregnancy. When a single baby stops growing, the body either expels the fetus, resulting in a miscarriage or a stillborn baby, or a doctor removes the tissue for the safety of the mother. But when a twin is lost late in a pregnancy a few different things can happen.
"If you lose a twin after 20 weeks, you are at a much higher risk to lose the other one. There's so much tissue present that the body wants to expel it and take the live one with it," Dr Givens explains, "The major risk to losing a twin when the other isn't ready to be delivered, is the prematurity of the surviving twin."
On the other hand, if non-living tissue remains in the uterus, the mother is at risk for coagulation problems caused by proteins from the tissue releasing into the mother's bloodstream. This can cause a condition called Disseminated Intravascular Coagulation that rarely can lead to complications that can result in the death of the remaining baby. If you are in this unusual situation, a specialist will monitor you for changes.
In extremely rare cases, a late-term twin actually vanishes too. Sometimes the water from the non-viable fetus is reabsorbed into the mother's body, but the weight of the surviving twin compresses the remaining fetal tissue and forms a "fetus papyraceus"—a flattened, paper-like thickening in the wall of the amniotic sac, which can only be seen after delivery.
The Emotional Toll
In my experience–and everyone's is different–Vanishing Twin Syndrome is like simultaneously hosting a birthday party and a funeral in the same room. You're thrilled and relieved that you've got a healthy baby growing bigger and stronger, while you're mortified that you're carrying a dead baby in your belly and heartbroken by the loss of a child you longed for so desperately. As a fertility specialist, Dr. Givens sees a large number of initial multiple pregnancies that ultimately result in a single live birth. She says, "Prospective parents generally have mixed feelings when they lose a twin. In the fertility world, a lot of times people don't have kids, this is their first pregnancy, and the loss is almost universally a sad thing for them. But it depends on whether they really wanted twins to begin with. Sometimes couples are a little relieved if they already have children and don't want twins. Either way we tell them that the twin wasn't healthy, so the loss was actually a positive thing, although it might not feel that way at the time."
Could You Be a Twin?
Could you be the surviving half of a twin pregnancy? Could you have been pregnant with twins and not known it? As reported by Lawrence Wright in The New Yorker, Professor Charles E. Boklage, a developmental biologist at the East Carolina University School of Medicine and a well-known twinning expert says that Vanishing Twin Syndrome "is much too common to be considered phenomenal, and it occurs for too many reasons to be considered any kind of syndrome." He contends that since most pregnancies fail in the early weeks—often unbeknownst to the mother—the early loss or disappearance of a twin is to be expected. Dr. Boklage estimates that for every set of live twins there are at least six singletons who are survivors of twin conceptions. He says, "Somewhere in the vicinity of ten to fifteen percent of us—and that's a minimum estimate—are walking around thinking we're singletons when in fact we're only the big half!"