Ovarian Hyperstimulation Syndrome (OHSS) in Pregnancy: Risks, Timeline & Success Rates

IVF Complications & Safety

Your guide to Ovarian Hyperstimulation Syndrome in pregnancy

Dr. Sony Sherpa (MBBS) 

Registered Obstetrics & Gynecology consultant - Medical Content Reviewer

Dr. Sony Sherpa is a board-certified Clinical Physician and practicing Medical Officer in the emergency department of a leading hospital. She earned her MBBS from Guangzhou Medical University with multiple academic scholarships, highlighting her dedication to medical excellence.
In addition to her clinical experience, Dr. Sherpa is a published medical researcher and holistic health advocate. Her dual expertise in emergency care and alternative therapies brings a unique lens to medically reviewed content—ensuring it is both accurate and accessible.

Last Updated: 01 April 2026  Medically Reviewed  10 min read  Evidence-based 

You have likely spent years imagining the moment those two parallel lines would finally appear on a pregnancy test. Now that you’re here, you are living a new reality, hosting a tiny embryo that is already changing everything inside you. However, for some, this long-awaited joy is coupled with a physical challenge that feels anything but miraculous: Ovarian Hyperstimulation Syndrome (OHSS).

It is completely natural to feel a blend of excitement and physical overwhelm as you move through your first trimester after IVF. You might feel like a bundle of nerves, and for good reason, as your body is performing the intense double-duty of recovering from hyperstimulation while beginning the profound work of growing a new life.

If your pregnancy feels different or more difficult than you expected, there is a medical reason for it. OHSS is a side effect of the fertility treatments that helped you conceive, and while the symptoms can feel scary, they are often associated with a strong ovarian response. Understanding exactly what is happening in your body can help you move from a place of anxiety to a position of control.

Quick answer

Ovarian Hyperstimulation Syndrome in early pregnancy happens when high hCG levels make your blood vessels leaky. Fluid moves into your abdomen and chest, and you feel bloated, short of breath, and unwell. Symptoms usually settle by weeks 10 to 12, and about 87% of women with severe late onset OHSS still go on to have a live birth.

Next step: If you notice rapid weight gain, much less urine, or trouble breathing, contact your clinic or emergency services the same day you noticed even one of the above-listed symptoms.

What the Latest Research Shows

Large studies from the United States, Europe, and Asia now give a clearer picture of how OHSS affects pregnancy. Some show higher rates of preterm birth, small babies, and early breathing problems. Others find that when OHSS is treated promptly, and you carry one baby, outcomes look very similar to other IVF pregnancies.

All research citations in this guide include PubMed links so you and your doctor can read the original studies if you wish.

In This Guide

• Why OHSS Happens
• How Doctors Grade Mild to Critical OHSS
• Pregnancy Outcomes and Risks
• How Doctors Treat OHSS
• How Clinics Try to Prevent OHSS
• Emotional Health and Coping
• What to Expect Week-by-Week
• Choosing Your Clinic and Care Team
• Frequently Asked Questions

How Often It Happens

Moderate to severe OHSS occurs in 1 to 5 out of 100 IVF cycles

Pregnancy Link

Risk is 2 to 5 times higher when the cycle leads to pregnancy

Live Birth Chance

About 87% live birth rate in severe late-onset OHSS

The Biology Behind OHSS: Why It Happens

The core problem in OHSS is a sudden jump in how leaky your small blood vessels become. Human chorionic gonadotropin, or hCG, drives this change. That hCG comes either from your trigger shot in an early-onset case or from your own rising pregnancy hormone in a late-onset case.

hCG acts on your ovaries and pushes them to release powerful signaling proteins. One of the most important is Vascular Endothelial Growth Factor, VEGF. When VEGF levels climb, protein-rich fluid starts to move out of your blood vessels and into the spaces around your organs. This is how you end up with fluid in your abdomen, called ascites, around your lungs, called pleural effusion, or around your heart, called pericardial effusion.

As this fluid shifts out of your blood vessels, your blood becomes thicker because it has lost some of its liquid part. Doctors call this hemoconcentration. This change is one reason you feel so drained and unwell during a severe flare of OHSS.

Your embryo is tiny, but it is already running the show hormonally. The early placenta grows into the upper part of your uterus and produces hCG. That same hCG that supports your pregnancy also keeps the "fire" of OHSS going in those early weeks.

OHSS in Pregnancy: Timeline from symptom peak to recovery, and how outcomes compare.

How Doctors Grade Mild to Critical OHSS

Doctors use standard grading systems, such as the Golan classification, to describe how severe your OHSS is. When you know where you sit on that scale, the situation often feels a little less frightening.

Are you struggling to find a comfortable position to sleep because your abdomen feels tight and heavy? If you reach a point where you cannot keep down food or drinks, or you notice that you are drinking a lot and passing very little urine, you need urgent medical care. In that situation, hospital treatment protects both you and your baby.

Pregnancy Outcomes and Risks

OHSS is serious, and you deserve straight answers. You also deserve to hear the good news that anxiety often drowns out.

• Preterm Birth and Birth Weight: Studies show that pregnancies complicated by OHSS are roughly twice as likely to end in preterm birth before 37 weeks. Babies are also almost five times more likely to be small for their gestational age compared with babies from IVF cycles without OHSS. A large United States registry analysis found a higher rate of low birth weight in the OHSS group, 12.2% compared with 9.4%, and more preterm delivery, 15.4% compared with 11.9%.
• The Multiples Factor: Twins or higher-order multiples add a lot of strain. In twin pregnancies, OHSS is linked to delivery almost a week earlier on average, 34.6 weeks compared with 35.6 weeks.
• Newborn Monitoring: A study including about 29,000 IVF births found that babies born after OHSS were almost twice as likely to have early breathing problems, such as respiratory distress or very fast breathing, soon after birth. Even when birth weight looked good, these babies needed closer observation in the newborn period.
• Long-Term Outlook: A 28-year review of more than 351,000 births found that OHSS did not raise the overall rates of high blood pressure in pregnancy, gestational diabetes, or cesarean birth when you comparing women with OHSS to other fertility patients. The main extra risk was in the IVF subgroup, where OHSS was linked to more very early births before 34 weeks.

Put simply, OHSS raises the odds of some complications, especially early birth and size concerns for your baby. At the same time, most women with well-managed OHSS still deliver healthy babies, especially when they carry one baby and receive careful follow-up.

How Doctors Treat OHSS in Pregnancy

If your OHSS is severe, your doctors focus on three main jobs: managing your fluids, preventing blood clots, and removing extra fluid from your abdomen and chest when needed.

Fluids and Electrolytes

Your team usually starts intravenous fluids to keep your blood volume stable and protect your organs. They use normal saline rather than Lactated Ringer's because OHSS tends to lower your blood sodium level. If standard fluids are not enough, they sometimes add concentrated solutions such as 25% human albumin. This kind of fluid helps pull water back from your third spaces into your bloodstream.

Paracentesis, the “Tap”

If your abdomen is very tight or you feel short of breath from pressure on your lungs, your doctor can perform a paracentesis. This is a drainage procedure guided by ultrasound, often using a transvaginal route similar to your egg retrieval. They drain off some of the fluid in your abdomen.

This is not just about comfort. Once the pressure drops, your kidneys usually start working better, and you begin passing more urine. Many patients describe a clear turning point after a tap, even when only a moderate amount of fluid is removed.

Preventing Blood Clots

Thickened blood and prolonged rest increase your risk of clots. That is why your doctors often prescribe low-dose heparin or low molecular weight heparin and ask you to wear compression stockings. There are case reports of clots in major veins such as the internal jugular or subclavian veins, and even in arteries in the brain. Preventing these clots is one of the most important parts of your care plan.

How Clinics Try to Prevent OHSS

If you are still at the planning stage, your team may be able to stop OHSS before it starts. Experienced clinics now keep rates of moderate and severe OHSS well under 5% of stimulated cycles by adjusting medication doses, trigger types, and transfer strategies.

One of the biggest tools is the freeze-all approach. If your clinic sees clear warning signs, such as more than 30 growing follicles or very high estradiol levels on the day of the trigger, they may advise freezing all embryos and delaying transfer. By doing that, they remove the second big wave of hCG that comes from an early pregnancy, and that usually drives the worst form of OHSS.

Emotional Health and Coping With OHSS

If you are going through OHSS in early pregnancy, it is no surprise that your nerves feel frayed. Your body is swollen, you may be short of breath, and you are terrified of losing the pregnancy you worked so hard for.

Does every thought, from the moment you wake up until you fall asleep, circle back to “Is my baby okay?” You are not dramatic, you are human. Your hormones are changing quickly, and your nervous system is very alert. Sudden crying spells, feeling out of control, or forgetting small things are all part of this phase.

Here are a few simple tools that many patients find helpful:

• The Diary Method: Choose a notebook that feels special and write down every fear as it comes. When you see your worries on paper, it becomes easier to sort out what belongs in a medical conversation and what comes from past hurt or exhaustion.
• Simple, Honest Conversations: Talk to your partner out loud, not just by text. Tell them what you are scared of and what you need. Feeling heard often calms your body as much as any medication.
• Mindful Breathing: Even a few minutes of noticing your breath can ease the tight feeling in your chest. Once your doctor says it is safe, gentle prenatal yoga or stretching can help you feel a bit more like yourself and rebuild trust in your body.

What to Expect Week-by-Week With OHSS

If you are dealing with OHSS in early pregnancy, the next steps usually follow a rough pattern. Knowing what is ahead can make the road feel less frightening.

• Weeks 4 to 8: This phase is when the endogenous hit from your own hCG shows up. Your embryo implants and hCG levels climb, so OHSS symptoms often peak or flare again. Your clinic may bring you in more often for ultrasounds to check the ovarian size and fluid collections.
• Weeks 9 to 12: For most women, this is when OHSS starts to calm down as the first trimester ends. Severe cases sometimes last longer, in rare situations, until week 21, and may require repeat paracenteses.
• Transitional Care: Once OHSS settles, your pregnancy will be like any other IVF pregnancy. You move into routine visits, including your 12-week scan and later anatomy scans.
• Postpartum Recovery: Your ovaries slowly shrink back to their usual size, which can take weeks or a few months after birth. Your uterus also needs time to contract. Do not feel discouraged if you still look pregnant right after delivery. Your body just did something huge and needs space and time to recover.

Typical OHSS timeline across early pregnancy, symptom peak, and recovery.