1. Difference between multi-fetal reduction and selective feticide
- Multi-fetal reduction refers to reducing the number of fetuses in high-order pregnancies, mainly for minimising the associated pregnancy complications. This is commonly considered for triplet (3 fetuses) pregnancies and usually advised for even higher order pregnancies such as quadruplets (4 fetuses) and quintuplets (5 fetuses). Occasionally, some women with twin pregnancies might also want multi-fetal reduction to singleton pregnancy.
- Selective feticide refers to terminating selectively the fetus diagnosed to be abnormal. It is therefore very important to ensure that the fetus identified is the affected one.
2. The pros and cons of multi-fetal reduction
- The main benefit is to lower the risks of preterm birth related to high-order pregnancies. The average gestational length for twins, triplets, quadruplets and quintuplets are 36, 33, 31 and 29 weeks respectively. In triplet pregnancies, it has been shown that the average gestational length can be prolonged to 36 weeks following multi-fetal reduction to twins.
- The main risk of multi-fetal reduction (and also selective feticide) is a 5-10% loss of all fetuses. Other risks include infection and preterm rupture of membranes.
3. Importance of chorionicity
- The chorionicity is important in multi-fetal reduction or selective feticide. In majority of cases, the fetuses do not share the placenta with others and the procedure involves injection of medication to the fetal heart under ultrasound guidance. However, for fetuses sharing the placenta, medication injected to one fetus may flow to the other via the placenta. Also, the death of one fetus might lead to an ischaemic vascular event on the other through the vessels in the connected placentae. Therefore, for fetuses sharing the same chorion (placenta), the procedure involved will be more sophisticated. They include radiofrequency ablation or fetoscopic cord coagulation.
4. Planning for multi-fetal reduction
- It is recommended to have a consultation with a maternal fetal medicine specialist who will perform this procedure at 9-10 weeks. This allows discussion on the benefits and risks, the procedure involved, and to allow some time to think about it. Ultrasound at this stage can determine accurately the chorionicity of the high-order pregnancies.
- Some higher order pregnancies will have spontaneous reduction in the first trimester, i.e. from triplets to twins by itself. Therefore, the procedure might not need to be performed.
- The procedure should ideally be performed after 11-13 weeks of gestation. An ultrasound scan for nuchal translucency and Downs screening can be arranged prior to the multi-fetal reduction procedure. Ultrasound should also look for gross malformation in any fetuses at this stage.
- For selective feticide, the procedure is arranged only when fetal abnormality is diagnosed. It may be performed at a later gestation. In Hong Kong, it can be arranged before 24 weeks of gestation.