Perhaps surprisingly, an undescended testicle (or two) at birth is a fairly common problem. Known technically as cryptochidism, it affects roughly 3 in 100 full-term boy babies, and 30 in 100 preterm boy babies. To parents, it may appear that a baby is missing a testicle, but really, it’s just that the ball hasn’t ‘dropped’ into the scrotum.

International medical guidelines advise a surgery known as an orchidopexy, or orchiopexy, before 18 months to assist the testicles’ descent into the scrotum. However, globally, more than three-quarters of baby boys with this testicle problem only receive surgical correction after 18 months of age. The problem is, the 18-month mark is really important for baby boys. Undescended testes have been linked to reduced fertility and increased risk of testicular cancer later in life — and the likelihood of both complications increases the longer surgery is delayed, as a new study shows.

Researchers at the University of Sydney have found that for every six months’ delay in orchidopexy beyond 18 months of age, the risk of testicular cancer in later life increased by 6%; the likelihood of having to use assisted reproductive technology (like IVF) later in life increased by 5%; and the likelihood of becoming a biological father at all dropped by 1%.

“Early surgery can reduce the risk of malignancy and male infertility, and ultimately has the potential to reduce future adult male reproductive disorders,” says Natasha Nassar, a perinatal and pediatric epidemiologist at the University of Sydney. Nassar is the senior author of the study, published in the journal The Lancet Child & Adolescent Health, which arrived at these conclusions by following 350,835 boys born in Western Australia between 1970 and 1999, until 2016. Nassar’s team tracked the boys’ hospital admissions, birth defect diagnoses, surgery dates, cancer diagnoses (if any) and use of assisted reproductive technologies as adults.

They found overall, baby boys in the study, as adults, were twice as likely to develop testicular cancer later in life; twice as likely to seek fertility assistance, and 21% less likely to have biological children. They also found hypospadias, another common birth defect in baby boys in which the opening to the urethra doesn’t form in the typical location on the head of the penis, was also associated with a reduced likelihood of biological fatherhood.

“Before this study, there was no evidence-based information on the impact of early surgery on the future risk of testicular cancer and infertility in adult males,” says study leader, Francisco Schneuer, PhD, a professor of public health at the University of Sydney. “Early diagnosis, ongoing examination and monitoring by parents and health practitioners and timely referral to surgery of boys with undescended testes is important to ensure adherence with guidelines.”