High Blood Pressure Risk for Mothers and Babies of Frozen Embryo Transfer

Recently, a group of researchers from Italy reviewed lots of other research studies to determine the answer to a question: Does a pregnancy resulting from a programmed frozen embryo transfer lead to a higher chance of pre-eclampsia and other high blood pressure illnesses compared to natural frozen embryo transfer? Let’s break that apart a bit more.

Programmed Frozen Embryo Transfer?

First, what is a frozen embryo transfer or FET? Approximately two million births a year come from in vitro fertilization. In general, this means that sperm from a donor (usually a father) and eggs from a donor (usually someone who wants to be a mother) are combined in a lab to generate a fertilized embryo. These embryos can be injected into a mother soon after being fertilized or they can be preserved by freezing. Whenever the owner of the embryos (usually a potential mother or existing mother who wants another child) decides to use the embryos, they will be “thawed” and inserted into the potential mother. For years, researchers and clinicians have been working to understand if the experience of these embryos and their mothers is any different from normal child birth or insertion of embryos that have not been frozen. In addition, there are different ways of stimulating the production of an egg in a women before fertilizing it. This can be done based on her natural cycle or with medication that “programs” the production of an egg off her normal cycle. This is the focus of the research here. Researchers sought to find out if the programmed approach is different from the natural approach.


The second question here is preeclampsia. Preeclampsia is a potential condition that can arise during pregnancy. The condition usually includes high blood pressure and high levels of protein in urine (called proteinuria). Other possible symptoms are: lower levels of platelets (a component of blood), increase liver enzymes (chemicals in the liver that help it function), severe headaches, changes in vision – such as temporary loss of vision or blurred vision, shortness of breath – sometimes caused by fluid in lungs, pain in the upper belly, and nausea/vomiting. It often starts after 20 weeks of pregnancy. If the condition is not treated appropriately, it can lead to greater harm. Treatment usually includes more intense monitoring by clinicians and medication to lower blood pressure. Sometimes the condition can occur after birth. This is called postpartum preeclampsia.

Researcher’s Theory and Findings

So, now back to the research study. The researchers analyzed a number of other studies to determine if these studies agreed or disagreed on the connection between programmed frozen embryo transfers and pre-eclampsia and other high blood pressure conditions. This kind of research is called a “meta-analysis.” In their meta-analysis, the researchers found that the transfers increased risk of preeclampsia, but there was no clearly supported recommendation to address this risk. Based on 19 studies, programmed frozen embryo transfer increase the risk of a number of conditions including: high blood pressure disorders of pregnancy, preeclampsia, postpartum bleeding, and cesarean section when compared with natural frozen embryo transfer. The risk was based on twelve “very low quality” studies for high blood pressure disorders of pregnancy and eight studies of “low quality” for risk of preeclampsia. However, even with the low numbers the risk of preeclampsia is approximately double in women exposed to programmed frozen embryo transfer. Some other conditions that mothers were at risk for include: placenta previa, cesarean section, preterm birth, and large for gestational age.

What’s happening?

The question is what is going on? As with many research findings, the exact pathway between increased risk and outcome is not clear without much more detailed research. However, one factor is different between these frozen embryo transfer approaches. The programmed frozen embryo transfer process lacks a corpus luteum. However, no exact mechanism by which this leads to preeclampsia has been figured out. Some researchers think the corpus luteum produces certain factors that counteract or prevent preeclampsia such as relaxin.

Acting on the Research
This research is useful for those who are considering in vitro fertilization. Preeclampsia and some of the other conditions that may arise from programmed frozen embryo transfer can be life threatening. Potential mothers have to balance the risks associated with this procedure along with the benefits of it to understand whether to engage in programmed frozen embryo transfer or not.

Perry Payne
Dr. Perry Payne is a public health practitioner and scholar with expertise in quality of care, health equity, prescription drug policy, and health care ethics. He has over ten years of experience as a freelance health care/medical writer and editor. His full-time work experience includes working as a professor and researcher in universities, serving as a federal government official, and a brief stint working for healthcare technology companies.

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