Managing risk—to mother and fetuses—in a twin gestation

Some parents elect fetal reduction

Given the high level of risk in a multiple pregnancy, reducing the number of fetuses is an option that some patients choose. A recent trend toward reduction to singleton pregnancy seems to be related to:

• increasing maternal age
• single parenthood
• financial considerations
• the increased medical risk to mother and fetuses associated with twins.³⁵

Evans and colleagues found that, although the overall rate of reduction from twins to a singleton was 3%, the percentage (76%) of women older than 35 years who opted for such a reduction was disproportionately high.³⁶

In a series of 1,000 cases of multifetal pregnancy reduction, Stone et al found that the pregnancy loss rate was lowest (2.5%) when there was reduction to a singleton gestation.³⁷ A comparative analysis of 2,000 cases of multifetal pregnancy reduction presented at the 2006 meeting of the Society for Maternal–Fetal Medicine found that the percentage of twin gestations undergoing reduction to a singleton has increased from 4% to 15.6% between 1999 and 2006, with an increase in the overall incidence of reduction to a singleton from 11.8% to 31.8%.³⁸

You should discuss pregnancy reduction with patients at high risk of pregnancy-associated complications such as cervical incompetence, preterm delivery, severe maternal cardiac disease, hypertension, diabetes, and uterine anomalies, as well as with patients who are carrying higher-order multiple gestations, in which the fetuses are at risk of problems.

Wrap-up: The tasks facing you in a multiple gestation

Start your management of a multiple gestation by taking the essential first step of determining the chorionicity of the fetuses.

Once you have done that, explain the risks of twin pregnancy and the particular risks of a single-sac pregnancy. Parents will want to know their risk of having a child with an anomaly; pay particular attention to the likelihood of a Down syndrome child. Noninvasive screening for Down syndrome and other chromosomal anomalies may be sufficient, but an older mother may prefer more definitive answers from CVS or amniocentesis.

You must prepare parents of a twin gestation for the risk of premature delivery. Cervical length assessment in the second trimester to early-third trimester may provide some indications of what is to happen, but the predictive value of this procedure is limited, and a shortened cervical length should be interpreted with caution.

In a monochorionic pregnancy, fetal growth should be assessed at regular intervals to evaluate for possible growth restriction or TTTS. If you detect evidence of abnormal fetal growth or amniotic fluid, US surveillance is indicated. Routine antepartum US surveillance of twins is not, however, recommended.²

The authors report no financial relationships relevant to this article.