What Is Embryo Reduction in a Multiple Pregnancy?

Embryo reduction is used when the mother is pregnant with more than two embryos and there's a risk for both the mother and the babies. Keep reading to learn more.
What Is Embryo Reduction in a Multiple Pregnancy?

Last update: 09 September, 2021

Embryo reduction is an operation that’s taking place more and more frequently. It’s a technique that consists of reducing the number of fetuses in multiple pregnancies. That is, it occurs in women pregnant with twins, triplets, or quadruplets. etc.

The reason why it’s performed is that multiple pregnancies pose a much greater risk than single pregnancies. They can negatively influence the mother and also cause complications in the babies.

Therefore, this intervention increases the chances of successful delivery. In this article, we’ll explain what embryo reduction is, what it entails, and how to deal with this decision.

What does embryo reduction consist of?

Before explaining embryo reduction itself, we need to explain why the technique is sometimes necessary. A multiple pregnancy is one in which two or more embryos develop simultaneously in the maternal uterus.

These embryos can come from the fertilization of one egg (monozygotic pregnancy) or two (dizygotic pregnancy). In other words, a multiple pregnancy is one in which twins, triplets, quadruplets, or more babies are developing.

According to an article in Aísa Reproducción y Biotecnología, multiple pregnancies have a greater morbidity and mortality rate, both for the mother and the embryos. In fact, according to estimates, maternal complications are between 3 and 7 times more frequent than in single pregnancies.

For this reason, on some occasions, the risks are unacceptable and embryo reduction is the best medical option. Multiple pregnancies frequently appear after assisted reproduction techniques. This only increases the problem, as the decision is more complex.

Embryo reduction is also known as multifetal pregnancy reduction. It consists of the interruption of the development of one or more fetuses, in the context of a multiple pregnancy.

It’s a technique that experts recommend when the risk is very high, both for the mother and for the babies. The idea is to improve the gestational conditions so that at least one or two healthy fetuses can be born.

An dropper dropping the image of a tiny fetus into a test tube.
Assisted reproduction techniques often result in multiple pregnancies.

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Embryo reduction is recommended in the context of high-risk multiple pregnancies. As a publication in Reproducción Asistida points out, it usually takes place when there are more than three embryos (triplets or quadruplets).

The reason is that pregnancies with twins or even triplets don’t pose as much risk if the mother is in good health. The risk increases in specific situations, such as when one of the fetuses experiences intrauterine growth retardation. The reduction is also performed to prevent premature delivery.

Another reason why this technique is recommended is to prevent cardiovascular complications in the mother. Likewise, doctors attempt to prevent hemorrhage and rupture of the uterine wall.

Although it’s somewhat more complex, families themselves may request embryo reduction. Especially in cases where there are economic difficulties.

How is embryo reduction performed in multiple pregnancies?

Embryo reduction is an intervention that usually takes place at the beginning of pregnancy. Ideally, doctors perform it between week 10 and week 13, after the first ultrasound scan.

The main reason why this doesn’t take place earlier is that there’s the possibility of the embryos shrinking during the first weeks. In addition, it’s impossible to evaluate certain ultrasound features until week 12.

For example, the nuchal fold or heart rate. These parameters are those that guide doctors to suspect that there’s a high risk in gestation. Likewise, it’s during these weeks they determine whether the fetuses come from the same egg and whether they share a placenta.

Embryo reduction is an operation that’s similar to amniocentesis. It usually involves local anesthesia.

Two routes are available: Vaginal and abdominal. A doctor introduces a needle through either one until reaching the fetus to be reduced. To reach the fetus, they perform an ultrasound simultaneously to help guide the needle.

Once the doctor reaches the fetus, they inject a potassium chloride solution into the fetus’ chest, causing the fetal heart to stop. The tissues of the uterus then reabsorb the fetus, so there’s no need to remove it.

How do doctors choose which fetus to remove?

There are two different types of embryo reduction, depending on whether or not the fetuses to be removed are chosen.

The first type is selective reduction. It’s best when one of the fetuses already expresses characteristics that indicate anomalies. For example, congenital defects or a developmental deficit. The idea is to reduce this fetus because it’ll be the one least likely to survive.

The second type is non-selective reduction. In this case, it takes place without pre-selecting any fetus. The specialist removes the fetus that’s in the most accessible position for insertion of the needle into the thorax.

The possible risks of the technique

According to a study published in the Cuban Journal of Obstetrics and Gynecology, embryo reduction is a safe technique. The rate of total pregnancy loss is between 5% and 6%.

However, if the technique doesn’t take place, the rate of miscarriage is higher. In addition, the risk to the mother and the surviving fetus varies depending on when the reduction occurs and whether the fetuses share a placenta.

Either way, embryo reduction increases the likelihood of survival of the remaining fetuses. The reason is that it allows them more room to develop and improves their nutritional capacity.

However, there are also risks. Intra-amniotic hemorrhage and infection can occur. Similarly, delivery occurs before 37 weeks in almost 75% of cases. What’s more, the fact that embryo reduction may have psychological consequences for the mother is another important factor to consider.

A woman with two fetuses in her belly.
Twin pregnancies have fewer risks than triplet or quadruplet pregnancies, but they still have more problems than single pregnancies.

Embryo reduction is a difficult decision to make

Embryo reduction is a difficult decision for all parents. It’s normal to want all the babies in a multiple pregnancy to be born. That’s why there are always doubts as to whether it’s the best decision or not.

In other cases, parents make the choice for other reasons, such as financial problems. All this makes it a stressful intervention that’s complex to carry out and has a great emotional impact. That’s why it is always best to consult several specialists. It may even be beneficial to manage the situation with a psychologist.

It’s important for the family to have the support of their loved ones. The opinion of other parents who have gone through the same situation can also be helpful.

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