One or two embryos?

Recently, there has been a change in the number of embyos routinely transferred in IVF. We follow the recommendations made by the Board of Health and Welfare (Socialstyrelsen). Most couples receive only one embryo to reduce the risk for twins. Before 2003, most often two embryos were transferred resulting in 25% - 30% of treatments lead to twin births.

Aren't twins actually what you want when you have tried for so long to have children? Many couples feel this way. Today, most twin pregnancies go well but twins have a much higher risk for complications compared to single pregnancies. A twin pregnancy has a risk for retarded intrauterine growth of the children, premature birth, low birth weight, poorly developed organs  (primarily the lungs and immune system), intra-uterine nutritional deficiencies,  increased risk of infection or intracranial bleeding and thereby cerebral palsy (CP). The risk for CP is four times higher for twins than singletons. Half of all twins are born prematurely and it is eight times more common that they are born before 34 weeks of gestation. They also have a doubled risk that one or both are stillborn or die at birth.

This is the background for the Board of Health and Welfare’s regulations (SOSFS 2009:32) that came out in 2003. This clearly recommends that “after fertilization outside a woman’s body, generally only one fertilized egg should be transferred. This regulation is binding. Thus, a couple is not allowed to choose the number of embryos to be transferred regardless if the treatment is privately or publically financed. If the risk for twins is deemed minimal, two may be transferred.

Currently, we transfer one embryo in about 75% of all treatments. To determine if one or two should be transferred, we always use the Carl von Linné Clinic’s unique prognostic model (please see Science). Using this computer model and our embryo ranking system, we can determine when the chance of pregnancy is significantly improved by transferring two embryos without increasing the risk for twins. Additionally, we can determine the cases in which transferring one embryo gives almost the same chance of pregnancy as transferring two.

In which cases two embryos are transferred? This is often done in cases when the embryo development is not optimal, if the woman is older or if there have been several unsuccessful treatments previously. To qualify for two, the chance of pregnancy should improve significantly and the risk for twins minimal according to our assessment. The choice to transfer two embryos is never meant to obtain twins; it is only to increase the chance of pregnancy at all.

This unique method has improved the number of embryos leading to pregnancy and children. Additionally, the number of embryos that can be frozen (cryopreserved) has gone up. The pregnancy frequency per oocyte retrieval has remained high. Our model has been proven to maximize the chance of giving birth to a normal weight, healthy child. Simultanously, we have decreased the risk of complications for IVF pregnancies to the same level as spontaneous pregnancies due to the decrease in the number of twins.

We will offer you either one or two embryos to be transferred. We would like if you have thought in advance about how you feel about transferring two should you be offered this option. Even though the risk for twins is low, it still exists. If you cannot accept the risk of twins, you should only accept transfer of one embryo at a time.

For further information, please see ”One or two embryos?” in the Result section.