Understanding Late-Onset Ovarian Hyperstimulation Syndrome in Older IVF Patients

When it comes to fertility treatments like IVF, many people have heard of a possible complication after egg retrieval called Ovarian Hyperstimulation Syndrome (OHSS). But most studies focus on younger patients who experience symptoms soon after egg retrieval.

A new study published in the Journal of Ovarian Research looked specifically at women aged 35 and older to better understand what causes late-onset OHSS—a form that develops days or even weeks after the egg retrieval—and how it affects pregnancy outcomes.

What Is Late-Onset OHSS?

OHSS happens when the ovaries respond too strongly to fertility medications, producing many follicles and high hormone levels. This can cause symptoms like bloating, nausea, rapid weight gain, or abdominal discomfort.

Late-onset OHSS usually appears more than 10 days after the trigger shot, often after embryo implantation. It’s less common, but can be more severe because of rising pregnancy hormones.

What the Study Found

Researchers reviewed more than 13,000 IVF cycles in women aged 35 and older who had a positive pregnancy test after a fresh embryo transfer.

They found that late-onset severe OHSS occurred in about 0.34% of patients—so it’s quite rare. However, they identified several factors that increased risk:

• Higher estradiol (E2) levels on the trigger day
• More good-quality embryos retrieved
• Use of long or ultra-long stimulation protocols (rather than antagonist protocols)
• Lower total gonadotropin dose, suggesting a stronger natural ovarian response

How OHSS Affects Pregnancy Outcomes

While late-onset OHSS is a serious condition, this study brought reassuring news:

• Women who developed late-onset OHSS did not have worse pregnancy or birth outcomes.
• In fact, the live birth rate was slightly higher among those with OHSS (84% vs 73%).
• There were no significant differences in preterm birth, birth weight, or neonatal complications.

This means that, while OHSS requires careful management, it doesn’t necessarily reduce your chance of having a healthy pregnancy. However, pregnancy should be avoided for any case where OHSS is noted before an embryo transfer.

What This Means for Patients

If you’re 35 or older and undergoing IVF, knowing the signs and risk factors of OHSS is helpful—but it’s important to remember:

• Your care team closely monitors hormone levels and ovarian response throughout treatment.
• Modern stimulation protocols and trigger medications are designed to reduce the risk of OHSS.
• If late-onset OHSS does occur, it can usually be managed safely with careful medical supervision.

Questions to Ask Your Fertility Specialist

• What ovarian stimulation protocol will we use, and how does it affect OHSS risk?
• What are my hormone levels, and how do they influence monitoring?
• What symptoms of OHSS should I look out for after embryo transfer?
• What steps can we take to minimize risk if I respond strongly to medications?

The Bottom Line

Late-onset OHSS in women over 35 is uncommon and often manageable.
Understanding the risks helps you make informed choices and feel more confident in your IVF journey. At Genesis Fertility, we follow evidence-based guidelines and tailor every treatment plan to help patients achieve the best possible outcomes—safely and with compassion.

This information has been medically reviewed by Alexander M. Kotlyar, MD, FACOG. Director of Resident Education at Genesis Fertility.