Can Having Cancer While Pregnant Affect the Baby?

A cancer diagnosis during pregnancy can affect the baby, though not usually in the way most people fear. The cancer itself almost never spreads directly to the fetus. Instead, the primary risks come from the treatments used to fight the cancer, the timing of those treatments, the physical toll the disease takes on the mother’s body, and clinical decisions like early delivery that become more likely when cancer complicates a pregnancy. The good news is that when treatment is carefully timed and managed by a specialized team, many children exposed to cancer or its therapies in the womb go on to develop normally.

Can the Cancer Itself Spread to the Baby?

The placenta acts as a remarkably effective barrier against cancer cells. Unlike infections, which can cross from mother to fetus through well-known pathways, cancer cells are typically blocked by both the physical structure of the placental membrane and the immune surveillance systems active within it.¹ Direct transmission of cancer from mother to fetus is one of the rarest events in oncology.

That said, it has happened. A systematic review identified 72 documented cases across the medical literature in which cancer had metastasized to the placenta, the fetus, or both. In those cases, about a third involved confirmed fetal metastases, with melanoma and lung cancer being the most common culprits. The babies most often developed metastatic deposits in their lungs, scalp, or liver, and symptoms typically appeared around five months after birth. The mothers in these cases were overwhelmingly diagnosed during the third trimester, and almost none had received cancer treatment before delivery.² These cases represent the extreme end of a spectrum. For the vast majority of pregnant people with cancer, the tumor stays on the maternal side of the placenta.

The Biggest Risk Factor Is Treatment Timing

Chemotherapy poses the most clearly documented threat to fetal development, and the risk hinges almost entirely on when during pregnancy it is given. The first trimester is the danger zone. This is when the baby’s organs are forming, and exposure to chemotherapy drugs during that window carries a high rate of major birth defects. One large analysis found that chemotherapy given before 12 weeks of gestation was linked to major congenital malformations in roughly one in five exposed pregnancies.³ Case reports have illustrated how specific drug combinations given during weeks five and six of pregnancy can cause distinct abnormalities of the hands, feet, and jaw, consistent with disrupted cell growth at that particular embryonic stage.⁴

After the first trimester, the picture changes substantially. Once organ formation is largely complete, the rate of major birth defects from chemotherapy drops to about 3%, which is in line with what you would expect in any pregnancy regardless of treatment.³ This is why oncologists generally try to delay chemotherapy until the second trimester when the diagnosis allows it. If a pregnant person is diagnosed with an aggressive cancer in the first trimester, the clinical team faces an agonizing decision about whether to begin treatment immediately, delay it, or discuss pregnancy termination.

Not All Drugs Cross the Placenta Equally

Even when chemotherapy is given after the first trimester and the risk of structural birth defects drops, the baby is still exposed to some level of the drug. How much depends heavily on which drug is used. Research in animal models has found dramatic variation: some chemotherapy agents barely reach the fetus, while others cross the placenta freely. For example, paclitaxel, a drug commonly used for breast and ovarian cancers, was undetectable in fetal blood in mouse studies. By contrast, platinum-based drugs crossed the placenta so efficiently that fetal concentrations actually matched maternal levels. Other agents like doxorubicin and epirubicin reached the fetus at only about 5% of the maternal dose.⁵

These differences matter for treatment planning. Oncologists consider not just whether a drug is effective against the cancer but how much of it will reach the baby. No chemotherapy drug is considered completely without risk during pregnancy, and the interplay between how easily a drug crosses the placenta and when it is administered shapes the overall risk profile.⁶

Radiation, Surgery, and Newer Therapies

Chemotherapy is not the only treatment that raises questions during pregnancy. Radiation therapy poses its own set of risks to the developing baby, including malformations, reduced head size, intellectual disability, and an increased risk of childhood cancer. The severity depends on the gestational age at exposure and the dose the fetus receives. When radiation is needed, careful shielding and dose calculations are used to minimize fetal exposure, but some cancers located in the pelvis or abdomen make this extremely difficult.⁷

Surgery for cancer during pregnancy is considered relatively safe when timed well. The early second trimester is the preferred window because the critical period of organ development has passed, the uterus is not yet large enough to complicate the surgical field, and the risk of triggering preterm labor is lower than it would be later. Regional anesthesia is favored over general anesthesia when possible, and maintaining blood flow to the uterus and placenta is a priority. Urgent or life-threatening cancers may require surgery at any point in the pregnancy regardless of trimester.⁸

Immune checkpoint inhibitors, a class of drugs that has transformed cancer treatment in recent years, are a newer concern. Because these drugs work by unleashing the immune system, there are theoretical worries about immune-mediated damage to the pregnancy or the developing baby. A large analysis of global safety reports found that, overall, checkpoint inhibitors were not associated with higher rates of specific pregnancy or newborn complications compared to other cancer drugs. However, the combination of two checkpoint inhibitor types was linked to a much higher rate of preterm birth. A small number of cases involved suspected immune-related complications, including one case of fetal lung inflammation and another of temporary thyroid problems in a newborn.⁹ The data on these newer agents is still thin, and their use during pregnancy remains a careful risk-benefit conversation.

How Diagnostic Imaging Fits In

Before treatment can begin, the cancer needs to be staged, which usually means imaging. Ultrasound and MRI are preferred during pregnancy because they don’t involve ionizing radiation.¹⁰ When a CT scan or PET scan is medically necessary, though, the radiation dose to the fetus is generally low. Studies measuring actual fetal exposure from PET/CT scans in pregnant cancer patients have found doses that fall well within ranges considered acceptable when the scan is genuinely needed for clinical decision-making. Protocols can be modified to reduce fetal exposure further.¹¹ The fear of any radiation during pregnancy sometimes leads to delayed or inadequate staging, which can be more dangerous than the small dose the imaging delivers.

Birth Outcomes and Preterm Delivery

Even when treatment goes smoothly and the baby avoids direct harm from drugs or radiation, pregnancies complicated by cancer tend to have different outcomes than typical pregnancies. One of the most consistent findings is a higher rate of preterm delivery. A nationwide study found that planned preterm birth was roughly ten times more likely in pregnancies where cancer was present, and delivery before 32 weeks was even more disproportionately elevated.¹² Much of this prematurity is deliberate: doctors may schedule an early delivery to allow the mother to start or intensify treatment that would be too risky for the fetus, or because the cancer itself is progressing rapidly.

Babies born to mothers undergoing chemotherapy during pregnancy also tend to weigh less. One study found that infants exposed to chemotherapy in the womb had significantly lower birth weights than matched controls, a difference driven by both earlier delivery and restricted growth inside the uterus.¹³ Fetal growth restriction after the first trimester has been documented across several cancer types, suggesting it may result from both the treatment itself and the metabolic demands the cancer places on the mother’s body.¹⁴ The higher rate of medical interventions in these pregnancies, from induced labor to cesarean delivery, reflects the complexity of balancing two patients’ needs simultaneously.¹⁵

How the Cancer Itself Can Starve the Pregnancy

Treatment is not the only way cancer affects a developing baby. The disease itself can create a hostile metabolic environment. Cancer cells consume enormous amounts of energy and nutrients. In a pregnant person, this creates direct competition between the tumor and the growing fetus for the same resources. Cancer frequently triggers anorexia and weight loss, and the inflammatory molecules and breakdown products released by tumor cells can push the mother toward a wasting state called cachexia. When a pregnant person’s body is being depleted this way, the placenta and fetus can suffer even without any exposure to treatment at all.¹⁶ Hormonal disruptions, chronic inflammation, and the psychological stress of a cancer diagnosis can add further layers of indirect impact on fetal development.

Long-Term Outcomes for Children Exposed In Utero

Perhaps the most reassuring area of the research concerns what happens to these children as they grow up. Studies tracking children who were exposed to chemotherapy before birth have generally found normal development. One follow-up of children exposed to breast cancer chemotherapy in the womb found no significant cognitive abnormalities. Of the 37 children enrolled in school at the time of the study, only four reported any academic difficulties.¹⁷

Heart function is a particular area of interest because some chemotherapy drugs, especially anthracyclines like doxorubicin, are known to damage the heart in patients who receive them directly. Children exposed to anthracyclines in the womb have been followed for decades in some studies. One long-term follow-up tracked children from about age 9 to nearly 30 and found no clinical signs of heart dysfunction at any point. Echocardiograms remained normal throughout.¹⁸ Separate research has confirmed that cardiac dimensions and function fall within normal ranges in these children.¹⁹ These findings are encouraging, though researchers acknowledge that truly long-term anthracycline effects remain an open question, and ongoing monitoring is prudent.²⁰

One area where the data is more sobering involves the reproductive future of children who were exposed to chemotherapy before birth. A study comparing these individuals to the general population found they had substantially fewer children of their own as adults. Both men and women exposed in utero were affected, though the reduction was more pronounced in men. When compared to their unexposed cousins rather than the general population, the pattern persisted, suggesting the effect was not simply a reflection of family circumstances or shared genetics unrelated to the exposure.

Breastfeeding After Cancer Treatment

For mothers who want to breastfeed after delivery, the question shifts from fetal exposure to whether the drugs show up in breast milk. Research measuring chemotherapy concentrations in breast milk has found wide variation depending on the drug. For some agents, like cyclophosphamide, paclitaxel, and carboplatin, the amount passing into milk drops to very low levels within one to three days after a dose, potentially allowing breastfeeding between treatment cycles. Doxorubicin is more complicated because its active breakdown products also need to be accounted for, and cisplatin may expose the infant to meaningful levels, warranting extra caution.²¹ The decision about breastfeeding during cancer treatment is highly individualized and depends on the specific drugs being used, the dosing schedule, and how long the mother is willing to pump and discard milk between cycles.

What Prematurity Itself Does

It is worth separating the effects of cancer and its treatment from the effects of being born early, because prematurity itself is one of the biggest sources of complications for these babies. A child delivered at 32 weeks to allow a mother to begin aggressive chemotherapy faces the standard risks of prematurity: underdeveloped lungs, feeding difficulties, temperature regulation problems, and the need for intensive care. Some of the developmental concerns attributed to cancer treatment during pregnancy may actually stem from early delivery rather than drug exposure. This distinction matters because iatrogenic prematurity, meaning prematurity caused by medical decisions rather than spontaneous labor, is one of the most modifiable risk factors in these pregnancies. Current guidelines increasingly emphasize carrying the pregnancy as close to term as safely possible, avoiding early delivery purely for convenience or anxiety when the clinical situation allows continued treatment during pregnancy.

The push toward avoiding unnecessary early delivery reflects a broader shift in how cancer during pregnancy is managed. A generation ago, the standard advice often leaned toward termination or immediate delivery followed by aggressive treatment. Today, the evidence supports a more nuanced approach. Many cancers can be treated during pregnancy with acceptable risk to the baby, particularly when chemotherapy is timed after the first trimester, surgery is scheduled during the second trimester, and delivery is planned as close to 37 weeks as the clinical situation permits. A multidisciplinary team that includes oncologists, maternal-fetal medicine specialists, neonatologists, and anesthesiologists working together gives both patients the best chance at a good outcome.⁸

The Psychological Dimension

The stress of a cancer diagnosis during pregnancy is not just an emotional burden; it may have biological consequences for the baby. Elevated maternal stress hormones, chronic inflammation, and disrupted sleep and nutrition can all influence fetal brain development. Research has flagged psycho-biological stress as one of several indirect pathways through which maternal cancer can affect the child’s neurodevelopment, alongside treatment effects and prematurity.¹⁶ Disentangling the contribution of maternal stress from the contribution of chemotherapy or preterm birth is extremely difficult in human studies, so the size of this effect remains uncertain. But it is a real consideration, and it is one reason that psychological support for pregnant cancer patients is increasingly viewed as a clinical priority rather than a nice-to-have add-on.