Cystic fibrosis (CF) does cause infertility in most men and reduces fertility in many women, though the mechanisms are different for each. About 97 to 98 percent of men with CF are infertile due to a missing reproductive structure, while women with CF are typically subfertile rather than fully infertile, meaning conception is harder but often still possible.
Why Most Men With CF Are Infertile
The vast majority of men with CF are missing the vas deferens, the tube that carries sperm from the testicles through the penis during ejaculation. This condition, called congenital bilateral absence of the vas deferens (CBAVD), happens before birth. The same thick secretions that clog airways and digestive passages in CF also block and destroy the developing vas deferens while the baby is still in the womb.
The important thing to understand is that this isn’t a problem with sperm production itself. About 90 percent of men with CF and CBAVD produce sperm normally in their testicles. They also produce semen. The sperm simply have no way to reach the semen, so ejaculate contains zero sperm. Sexual function, libido, and hormone levels are otherwise normal.
Because the vas deferens is already gone by the time a baby is born, current CF medications cannot reverse the problem in adults. The structural damage is permanent. However, animal research has shown a glimmer of possibility: CF ferrets treated with a CFTR modulator drug during pregnancy developed normal vas deferens. Whether this could eventually apply to humans remains unknown.
How CF Affects Female Fertility
Women with CF face a different and more complex fertility picture. Rather than a single structural problem, several overlapping factors make conception harder.
The most significant barrier is thickened cervical mucus. The same protein malfunction that causes thick mucus throughout the body also affects the cervix, creating a physical barrier that sperm struggle to cross. Mouse studies have found that the number of sperm reaching the reproductive tract in CF models was roughly 10 percent of normal levels. This alone dramatically reduces the odds of natural conception. Supporting this theory, many women with CF have conceived through intrauterine insemination, a procedure that deposits sperm directly past the cervix into the uterus, bypassing the mucus problem entirely.
Beyond mucus, nutritional status plays a major role. Chronic lung infections and the high calorie demands of CF can lead to low body weight and reduced body fat. Women with higher BMI and better lung function are more likely to have regular menstrual cycles. When body weight drops too low, the hormonal signals between the brain and ovaries can weaken, disrupting or stopping ovulation. Some women with CF also show reduced ovarian reserve, though researchers are still working out whether this is a direct effect of the faulty gene or a downstream consequence of chronic illness and poor nutrition.
How Modern CF Medications Are Changing the Picture
The arrival of highly effective CFTR modulator therapies, particularly the triple combination of elexacaftor, tezacaftor, and ivacaftor (sold as Trikafta), has noticeably shifted fertility outcomes for women with CF. These drugs partially restore the function of the defective protein, thinning mucus and improving hydration across many organs, including the reproductive tract. They appear to decrease the thickness and increase the pH of cervical mucus, creating a more sperm-friendly environment.
The clinical effect has been striking. Two CF care centers reported that 14 women conceived after starting this triple therapy, seven of those pregnancies unplanned, and four occurring in women who had previously been evaluated and told they were infertile. Reports of unexpected pregnancies on this medication have become common enough that fertility counseling is now a standard part of starting treatment. If you have CF and are not planning a pregnancy, this is something to discuss with your care team before beginning or switching medications.
For men, the picture is less encouraging. Since the vas deferens is destroyed before birth, these medications cannot rebuild it. There is some possibility that CFTR modulators could increase ejaculate volume by improving fluid regulation elsewhere in the male reproductive tract, but they will not restore natural sperm transport.
Assisted Reproduction Options for Men
Men with CF who want biological children typically need a sperm retrieval procedure combined with a specialized form of in vitro fertilization. The most common approach involves surgically extracting sperm directly from the testicle or the epididymis (the structure where sperm mature, located next to the testicle). That sperm is then injected directly into an egg in a lab, a technique called intracytoplasmic sperm injection, or ICSI.
Success rates are encouraging. In one series, the pregnancy rate per cycle for men with CF undergoing ICSI was 50 percent, with a live birth rate of 62.5 percent per cycle. Earlier published series have reported similar figures, with pregnancy rates around 40 to 63 percent of couples and live birth rates near 47 to 50 percent. One notable challenge is that sperm retrieval can be more difficult in men with CF compared to those who have CBAVD without CF. About 70 percent of men with CF needed a backup retrieval technique during their procedure, compared to roughly 28 percent of men with CBAVD alone. Fertilization rates were also lower in the CF group (about 33 percent vs. 69 percent), though pregnancy and live birth rates were comparable once fertilization occurred.
Pregnancy Considerations for Women With CF
Getting pregnant is only part of the equation. Carrying a pregnancy safely requires adequate lung function and nutritional reserves. Current guidelines generally recommend against pregnancy when lung function (measured by FEV1) falls below 50 to 60 percent of predicted values, particularly if combined with low BMI. Severe pulmonary hypertension or heart complications from lung disease are considered absolute contraindications.
Even in women with good baseline health, pregnancy places real demands on the body. One 10-year study from a UK center found that lung function dropped moderately after delivery, and while some measures recovered by 12 months postpartum, a reduction in FEV1 of nearly 6 percent persisted a full year later. This doesn’t mean pregnancy is unsafe for women with well-managed CF, but it does mean careful planning and monitoring matter.
CF-related diabetes adds another layer of risk. Women with CF who have diabetes before or during pregnancy face higher rates of preterm delivery, lower birth weight, and lower gestational age compared to those without diabetes. Maintaining blood sugar within a normal range throughout pregnancy significantly reduces these complications, and early testing is recommended to catch glucose problems before they affect fetal development in the first trimester.
Genetic Planning and Carrier Screening
Any person with CF who is considering having children carries two copies of a faulty CFTR gene, meaning every child will inherit at least one. Whether that child actually develops CF depends entirely on the other parent. If the other parent is not a carrier, none of their children will have CF (though all will be carriers). If the other parent is a carrier, there is a 1 in 2, or 50 percent, chance each child will have CF.
Carrier screening is available and detects about 85 to 90 percent of carriers in people of European descent. Detection rates vary by ethnicity. A negative screening result significantly lowers the risk but does not eliminate it entirely, since rarer mutations may not be included in standard panels. For couples where both partners carry a CFTR mutation, each pregnancy carries a 25 percent chance of producing a child with CF, and preimplantation genetic testing during IVF can identify unaffected embryos before transfer.