Certain CF carriers have lower IVF pregnancy success, study finds
Disease-causing mutation linked to higher gestational diabetes risk
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Women who carry a mutation that can cause cystic fibrosis (CF) may be more likely to develop gestational diabetes, and carriers of certain CF-causing mutations may also have a harder time getting pregnant, according to a new study.
“These results support the concept that [being a CF carrier] may reduce female fertility,” researchers wrote. “Consequently, women should be informed that CFTR carrier status could diminish their probability of success with assisted reproductive technology.”
The study, “Impact of female CFTR variant carrier status on reproductive outcomes,” was published in the Journal of Cystic Fibrosis.
Studies suggest carriers may be at risk of CF-related health issues
CF is a genetic disease caused by mutations in the CFTR gene. This results in the production of abnormally thick mucus that builds up in organs to drive disease symptoms. For example, mucus in the pancreas can lead to CF-related diabetes. Issues with fertility are also common among people with CF.
Everyone inherits two copies of the CFTR gene, one from each biological parent. CF is an autosomal recessive disease, meaning that overt CF only develops if both copies of the gene carry a mutation. People who carry one mutated copy, along with a second healthy copy, are known as carriers.
Traditionally, it’s been thought that CF carriers do not develop any overt disease symptoms, but they can pass the disease-causing mutation on to their biological children. However, recent studies have challenged this idea, with data suggesting that carriers may be at higher-than-average risk of certain CF-related health issues, such as pancreatitis (pancreas inflammation).
In this study, two scientists in China explored whether being a CF carrier affects outcomes for women who are undergoing in vitro fertilization (IVF) with intracytoplasmic sperm injection (ICSI). IVF with ICSI is a type of assisted reproductive technology where egg and sperm cells are collected, and the sperm is then carefully injected into the egg cell using a specialized needle. Cells that successfully fertilize can then be implanted into the uterus with the aim of starting a pregnancy.
Overall rates of live birth similar among carriers and non-carriers
This analysis included more than 4,000 IVF/ICSI cycles in women who were not CF carriers, as well as 390 cycles from women who were CF carriers. Compared with non-carriers, the CF carriers had significantly lower rates of mature egg cells (78.4% vs. 84.1%). They also had lower average levels of follicle-stimulating hormone, a hormone that’s important in egg development.
Overall, rates of clinically confirmed pregnancy and live birth were similar among CF carriers and non-carriers. But differences were noted when the researchers performed more granular analyses looking at particular types of mutations.
Specifically, data showed that carriers of a specific CFTR mutation called 5T had similar outcomes as non-carriers: in both groups, each cycle had a chance of successfully initiating a pregnancy that resulted in live birth of slightly lower than 50%. But for carriers of certain other mutations, namely Q1352H, p.I125T, and R1070Q, pregnancy success rates were markedly lower, and only about 1 in 4 cycles resulted in a live birth.
CFTR carrier status was significantly associated with an increased risk of gestational diabetes mellitus …, suggesting a potential influence on glucose [blood sugar] metabolism during pregnancy.
The researchers noted that embryo quality did not differ based on CF carrier status, suggesting that problems with the embryo itself are unlikely to account for these differences. Instead, the researchers speculated that carrying one defective copy of the CFTR gene might lead to subtle changes in the endometrium (the lining of the uterus) that make it harder for an egg to implant.
Based on their findings, the researchers said that women who are known to be CF carriers should be counseled that they may have less success than average with assisted reproductive technologies like IVF/ICSI.
Among participants who did get pregnant, rates of gestational diabetes were significantly higher for CF carriers than non-carriers (28.2% vs. 10.9%) — a finding that has previously been reported in a different study, the researchers noted. Meanwhile, rates of preterm delivery were comparable, and outcomes for babies were also similar.
“CFTR carrier status was significantly associated with an increased risk of gestational diabetes mellitus …, suggesting a potential influence on glucose [blood sugar] metabolism during pregnancy,” the researchers wrote.
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