Introduction
As you navigate the myriad decisions involved in preserving your fertility, one question likely looms large: what are the risks associated with using a frozen embryo versus a fresh embryo in my pregnancy and in my baby? How different would my pregnancy and the health of my baby be between the two options? It is only natural to want clarity and reassurance as you weigh your options. Here we will explore what the differences are between fresh and frozen embryo transfers and potential risks in pregnancy and the baby.
Fresh versus frozen embryo
Fresh embryos are made when eggs and sperm are mixed in the laboratory in a procedure called in vitro fertilization, or IVF. An embryo is then placed in the uterus 2-5 days later while the remaining embryos are frozen for a later date, hence frozen embryos. Some women may also choose to freeze all of the embryos for a later date, instead of transferring one, if the plan isn’t to get pregnant right away. When the woman is ready for pregnancy, the fertility clinic would then thaw the frozen embryo for a thawed frozen embryo transfer.
How is pregnancy affected?
Overall, multiple studies have found that there are no differences in the number of pregnancy complications or miscarriage rate between the two strategies. The pregnancy rate also doesn't differ much between using frozen and fresh embryos, and embryo quality was not affected by the freezing process.
For frozen embryo pregnancies, there may be more likelihood of having a post-term delivery (pregnancy that extends beyond 42 weeks) and a reduced likelihood of a preterm delivery (childbirth before 37 weeks), which could lead to a larger newborn size.
How is the baby affected?
Between using fresh or frozen embryos, the rate of giving birth to a live newborn does not vary significantly. Studies also found that the health outcomes of newborn babies, including malformations and neurodevelopmental abnormalities, were not different between the two.
However, several studies have found that frozen embryos may lead to macrosomic newborns (likely due to the higher chance of post-term births, as mentioned above), or babies heavier than 4-4.5 kilograms (9-10 pounds), which may make delivery more difficult. But it also means there's less chance of babies with low birth weight, babies that are small for their gestational age, and premature births for those who choose frozen embryos.
Longer term outcomes in children also were not different between frozen embryo or fresh embryo births. Studies that examined children from 3 to 37 months after birth checked for prevalence of neurodevelopmental issues, growth and chronic diseases, and any abnormalities that occurred during pregnancy, and all tended to be equal between the two groups.
Other considerations
One major compounding factor to be taken into account is the age of the pregnant mother. With everything equal, the pregnancy rate with frozen and fresh embryo transfers don't differ. However, as you probably know, pregnancy rates, as well as maternal and neonatal health outcomes, are better at an earlier age. Over 40 years old, independent of whether frozen or fresh embryos were used, women may be at a higher risk for preeclampsia, gestational diabetes, fetal growth restriction, stillbirth, preterm birth, and operative delivery.
Another consideration is the risk of ovarian hyperstimulation syndrome, a rare but serious complication caused by fertility treatments that stimulate the ovaries to produce a large number of eggs. Those who elect frozen embryo transfer have a lower chance and milder presentation of ovarian hyperstimulation syndrome than those who use fresh embryo transfer.
Conclusion
As current evidence shows, the risks and outcomes related to frozen versus fresh embryos are comparable. Whether it's pregnancy rate, newborn and maternal health, or later developmental issues in children, there doesn't seem to be a major difference between the two. Apart from the consideration of maternal age and ovarian hyperstimulation syndrome, it's important to weigh the financial cost of both. In certain countries, it's more expensive to perform frozen embryo transfer than fresh. Given no major health advantage of one over the other, it'll be up to you to figure out which suits you better.
