Understanding Pregnancy Loss in Turner Syndrome

Most pregnancies affected by Turner syndrome end in miscarriage during the first or second trimester. The most common form of Turner syndrome, monosomy X, is one of the leading chromosomal causes of pregnancy loss worldwide, and only 1% will result in live birth. It is estimated that approximately 10% of all miscarriages involve Turner syndrome. 

Although only about 1% of pregnancies affected by Turner syndrome result in a live birth, many of the girls who survive go on to live long, fulfilling lives. While some experience medical or developmental challenges that require ongoing care, many attend school, build careers, form meaningful relationships, and pursue their goals just like their peers. But, why is this condition so fatal before birth? What causes 99% of fetuses to not survive? 

Through screenings during the first trimester of pregnancy, health professionals can find out whether the baby has Turner syndrome, though the diagnosis is often missed until later in life. Low levels of pregnancy-associated plasma protein A (PAPP-A) and/or excess fluid buildup is first seen in ultrasound scans and may raise doubts, which are confirmed thoroughly through amniocentesis or chromosome analysis. Learn more about Genetic Testing.

During early development, fetuses with TS usually have difficulty developing their lymphatic system, which responsible for managing the body’s fluids. For a fetus without TS, the lymphatic and cardiovascular systems work together to bring back and circulate fluid around the body. However, for a fetus with TS, there is fluid buildup inside the body, especially near the neck area, a condition called cystic hygroma. The fluid can become harmful since it creates pressure on the developing heart of the fetus, and is the main reason why the pregnancy is unable to go on in most cases. 

Although many fetuses with Turner syndrome do not survive to birth, a small percentage do. Some surviving individuals have mosaic Turner syndrome, meaning they have a mixture of cells such as 45,X and 46,XX (or less commonly 46,XY). Mosaicism may contribute to survival when enough cells provide the genetic instructions needed for normal development of the lymphatic system.

However, not all individuals who survive to birth have mosaic Turner syndrome, and researchers believe multiple factors—including the severity of associated heart or lymphatic abnormalities—also influence whether a pregnancy continues to term. While these individuals may still face health challenges related to Turner syndrome later in life, being born is often their first remarkable milestone.