Symptoms of miscarrying one twin, which is known as vanishing twin syndrome, include mild cramping, pain in the pelvic region, vaginal bleeding and a decrease in the level of human chorionic gonadotropin, or hCG, which can be detected via a blood test, according to What to Expect. Some women who miscarry one twin will experience no symptoms at all.
What to Expect points out that although these symptoms can be indicative that one twin has been miscarried, it is by no means a sure sign. Only an evaluation by a medical professional can determine whether or not a fetus has been lost.
Vanishing twin syndrome generally occurs during the first trimester of the pregnancy. Many times, it will occur before a mother even knows that she is carrying two fetuses. When it occurs early in pregnancy, the tissue from the miscarried baby is usually just reabsorbed by the mother.
When a twin is miscarried later in the pregnancy, it can cause hemorrhaging, infection or preterm labor. It also puts the baby at risk of intrauterine growth restriction. What to Expect notes that about 20 to 30 percent of multiple pregnancies are affected by vanishing twin syndrome and that the prevalence of the syndrome has grown over the past few decades due to advancements in early ultrasound procedures.