Selective reduction is done for both medical and non-medical reasons. Medical issues generally related to multiple births include premature births, low birth weights, and associated medical problems. Non-medical reasons include that the couple or the mother do not feel that they are emotionally or financially ready to handle more than one child. Selective reduction can also be used to reduce a twin pregnancy to a singleton one. This is a less common but growing practice as the risks in twin pregnancies, while existent, are much lower than in higher-order multiple pregnancies.
The reduction procedure is generally carried out during the first trimester of pregnancy. The most common method is to inject potassium chloride into the fetus's heart; the heart stops and the fetus dies as a result. Generally, the fetal material is reabsorbed into the woman's body. While the procedure generally reduces the over-all risk level for the remaining fetus or fetuses, reduction does have its own risks, including the possibility that one or more of the remaining fetuses will also die.
Dr. Mark Evans, a New York City-based obstetrician-geneticist, and a group of doctors, developed the procedure for selective reduction in the 1980s.
Pregnancy Outcome Statistics
Triple to twins reduction has statistically shown better pregnancy outcome with premature birth before 32 weeks reduced to 10.1% from 20.3% and miscarriage before 24 weeks reduced to 5.6% from 11.5%.
Reduction of triplets to a singleton has a higher loss rate (7 versus 4.5%) but lower morbidity, yet both resultant twins or singletons are much less risky than attempting to carry the triplets (15%).
Reduction from twins to singleton remains controversial. The 2010 retrospective case-control study found that twins to singleton reduction produced no statistically significant improvement in pregnancy outcome in terms of total pregnancy complications, preterm deliveries or birth weight. The pioneer of the procedure Mark Evans initially discouraged twins to singleton reduction, however he endorsed it in 2004 paper citing lower risk of total pregnancy loss after procedure (1.9%) compared to spontaneous loss (8-10%).
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- Komaroff, Anthony. Harvard Medical School Family Health Guide, page 913 (Simon and Schuster 1999): “Selective reduction is usually performed during the first trimester....”
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- EVANS, MARK. "Fetal Reduction From Twins to a Singleton: A Reasonable Consideration?". Health. Obstetrics & Gynecology.
- "The Two-Minus-One Pregnancy". Health. New York Times.
- HASSON, JOSEPH. "Reduction of twin pregnancy to singleton: does it improve pregnancy outcome?". Health. The Journal of Maternal-Fetal and Neonatal Medicine.