IVF and ICSI
How an IVF cycle works, from ovarian stimulation and egg retrieval to fertilization, ICSI, embryo culture and transfer, and how we keep treatment safe.
On this page
In vitro fertilization (IVF) is an emotional and financial commitment, so we consider simpler treatment paths first whenever they’re reasonable. For some patients with severe male or female factor infertility, though, IVF is the only option.
How an IVF cycle works
During an IVF cycle, hormonal medications stimulate the ovaries to produce more than one egg (oocyte), ideally about 5 to 10. The eggs are collected in a simple outpatient procedure through the vagina and fertilized with sperm in our laboratory.
Fertilization happens in one of two ways:
- The mature egg is surrounded with about 50,000 sperm.
- A single sperm is injected directly into the egg (ICSI).
The resulting embryos grow in culture for an average of five to six days. At that point you can freeze the embryos or go ahead with a fresh embryo transfer. One or more embryos are placed in the uterus, and the second half of the cycle (the luteal phase) is supported with progesterone, given vaginally or by injection. A pregnancy test follows about two weeks later, and any extra embryos are frozen for later use.
Ovarian stimulation
The main stimulation medication is a synthetic version of FSH, a hormone very similar to the one made by the pituitary gland in the brain. It encourages the ovaries to develop more than one egg. It’s usually combined with a second medication (an agonist or an antagonist) that stops the pituitary gland from triggering ovulation too early, before the eggs are mature and ready for fertilization.
When the follicles look mature, based on their size and estrogen levels, ovulation is triggered with an injection of hCG (human chorionic gonadotropin) or an agonist.
Choosing the right starting and maintenance doses, and timing the trigger shot carefully, are key to collecting a good number of mature eggs while keeping the risk of ovarian hyperstimulation syndrome (OHSS) low. Based on your age, ovarian reserve blood tests and the number of antral follicles on ultrasound, we anticipate whether you’re likely to be a high responder or a low responder, and plan stimulation to match.
If you’re a high responder
The goal is a moderate number of mature eggs, around 8 to 10, while avoiding OHSS. We use a lower dose of FSH and monitor your response often so the dose can be adjusted. Using a GnRH antagonist has an added advantage: the final trigger can be an agonist instead of hCG. Unlike hCG, the agonist doesn’t overstimulate the ovaries and isn’t associated with OHSS.
Lower-dose stimulation also reduces the possible harmful effects of high FSH doses on eggs and of very high estrogen levels on the lining of the uterus. It lowers the cost of stimulation, too.
If you’re a low responder
Here the goal is to improve how your ovaries respond by working with several aspects of ovarian physiology, including synchronizing the follicles before stimulation begins. Approaches include:
- Modified natural cycle. We avoid stimulating medications at first and follow your natural follicle growth. Once the follicles reach an advanced stage, their growth is supported with a very low dose of FSH.
- Estrogen and antagonist pretreatment. Taking estrogen and an antagonist before stimulation helps synchronize the follicles and can increase the number of eggs collected.
- Boosting your own FSH. Clomid or a “flare” Lupron protocol encourages the pituitary gland to make more of your own FSH.
You can read more in mild and minimal stimulation IVF.
ICSI and IMSI
With intracytoplasmic sperm injection (ICSI), a single sperm is injected into each egg in the lab. It’s used when the number or quality of sperm is low enough that the sperm may not fertilize the egg on its own, and it’s recommended for severe male factor infertility or when eggs fertilized poorly in a previous cycle.
Intracytoplasmic morphologically selected sperm injection (IMSI) is a specialized form of ICSI. A high-magnification digital imaging lens is used to choose sperm based on their detailed shape before injection. It may be considered when sperm shape (morphology) is abnormal or when fertilization failed after ICSI before.
Extended culture and blastocyst transfer
Embryos can be transferred to the uterus on day 3 after egg retrieval, or culture can be extended to day 5 or 6, the blastocyst stage. Growing embryos to the blastocyst stage allows better selection of the embryos that may have a higher chance of implanting. This approach is favored when there are 4 or more embryos and the plan is to transfer one or two.
Embryo transfer
Embryo transfer takes thoughtful planning. The aim is to place the embryos in the middle of the uterine cavity without damaging them or the uterine lining, and without triggering contractions of the uterus.
- We inspect the cervix to understand its shape and direction, and ultrasound shows the path of the cervical canal.
- A trial transfer is done beforehand to spot any difficulty, since a difficult transfer can lower the chance of pregnancy.
- The transfer itself is guided by abdominal ultrasound, so we can see the cervical canal and confirm exactly where the catheter tip is placed.
- Occasionally the cervix needs to be gently dilated before transfer, or the embryos are placed through the wall of the uterus instead of the cervical canal (trans-myometrial embryo transfer).
Keeping treatment safe
A healthy pregnancy is the goal, and reaching it as safely as possible matters just as much. The two most important risks of fertility treatment are OHSS and multiple pregnancy.
Ovarian hyperstimulation syndrome (OHSS)
Severe OHSS happens after heavy exposure to FSH followed by hCG. It’s more common in younger women and in women with PCOS. Symptoms include significant bloating, vomiting, diarrhea, fluid build-up in the abdomen (ascites), concentrated blood and a higher risk of blood clots.
We work to prevent OHSS by:
- Choosing your starting and maintenance FSH doses carefully
- Pausing FSH for a few days when needed (coasting)
- Using an agonist such as Lupron, instead of hCG, to trigger final egg maturation
- Sometimes canceling the fresh transfer and freezing all embryos for a later frozen embryo transfer
Multiple pregnancy
Twins and higher-order multiples carry a higher risk of preterm delivery, admission of the babies to intensive care, and sometimes long-term health problems. Parents carrying multiples face higher risks of anemia, high blood pressure in pregnancy, heavy bleeding after delivery and cesarean birth. Carefully deciding how many embryos to transfer keeps this risk low, which is why we often recommend single embryo transfer.
To see how IVF outcomes are reported, visit our SART-reported success rates.
This article is general information, not medical advice. Every situation is different, so talk with your doctor about yours.
