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Olivia: In 1977, for the very first time, a team of British researchers successfully fertilized a human egg in a dish and transplanted the embryo into the mother's body. The mother gave birth to a baby named Louise Brown, who is now almost 40 years old. The doctor who pioneered the procedure won a Nobel Prize for it, in 2010.

That procedure is now known as "in vitro fertilization" or "IVF." But a lot has changed since Louise was born. By studying IVF for the past few decades, scientists have made it a lot more effective, with fewer complications and better success rates. There are all kinds of reasons why two people might have trouble conceiving naturally. Like low sperm count or poor quality eggs.

By controlling the fertilization process in the lab, and then selecting the best embryos, doctors can use IVF to help people with fertility issues have a biological child. The basic procedure involves a few main steps. First, doctors make extra ovarian follicles form. They contain immature eggs, or oocytes. The process is called ovarian hyperstimulation, where they give the patient hormone injections, specifically hormones called gonadotropins.

As you might have guessed from the name, Gonadotropins affect the gonads, controlling sex hormone levels and egg and sperm production. Ovarian hyperstimulation stops the natural menstrual cycle and causes the ovaries to form multiple follicles. With all those follicles Lots of eggs can be collected at once, usually between 15 and 30, way more than the single egg that's released in a natural cycle.

Once the follicles have formed, doctors give an injection of a hormone called "Human Chorionic Gonadotropin" which makes the eggs mature. Then, they collect the eggs and incubate them with sperm in a special solution. Once the eggs are fertilized, they're grown in a dish for a few days as they start dividing.

Doctors choose the embryos that look the best for implantation and implant them directly into the uterus through the cervix. A lot of the time, they'll implant several embryos at once to increase the chances that one of them will attach to the uterine lining and grow. Since the 1970's, researchers have been working on advancing the science and technology behind IVF to lead to more healthy pregnancies. Ovarian hyperstimulation, for example, can have side effects like ovarian hyperstimulation syndrome, which can cause blood clots and kidney failure.

A different process called Natural IVF avoids some of the side affects of the extra hormones. Doctors just harvest naturally released eggs, but there's a down side. Only one egg can be collected at a time. And since IVF doesn't have a 100% success rate, patients often have to go through the procedure many times. Instead, Doctors can balance ovarian hyperstimulation and natural IVF in a process called Mild IVF. They give people shorter courses of lower doses of hormones to avoid some of the negative side effects while still encouraging the ovaries to produce multiple follicles.

Researchers have also been working on the problem of multiple births. One big criticism of IVF treatments is that it often results in twins, or triplets, or even more, and that's a lot of babies. More than most people are prepared for. Multiple births are so common because doctors tend to transplant a bunch of embryos since many of them don't make it. At least until recently.

We use d to only be able to grow viable embryos in a dish for about 3 days - to the cleavage stage, when the single-celled sperm and egg combo, or zygote, starts to divide into more, identical cells. In a natural pregnancy embryos in this cleavage stage would still be in the Fallopian Tube, between the ovary and the uterus. But, with IVF we stick them straight into the uterus.

It is tough for the 3-day old embryos to survive in there, so only about a quarter of those embryos lead to pregnancies. Doctors transplant more of them, to give a patient a decent chance of at least one surviving. Except that sometimes, they get lucky and end up with more than one.

But now we know what conditions to use to grow embryos for longer: up to 6 days, into the blastocyst stage. That's when the embryo hallows out as its dividing cells start to specialize, so they can eventually become things like heart cells and lung cells. By the time the get to the blastocyst stage, many of the embryos that wouldn't have been able to survive in the uterus, have already broken down.

So, almost half of the embryos implanted at this stage, lead to pregnancy. By growing embryos for longer, doctors can implant fewer of them into the uterus (usually 2-3 instead of 3-4) and have about the same rate of successful pregnancies. So there's less risk of quadruplets or octuplets.

Researchers have also figured out how to keep people from passing on mitochondrial diseases when the mother has a mutation in the special kind of DNA that lives in the mitochondria. They take the egg's cytoplasm, so all that watery stuff outside of the nucleus, and replace it with a third donor's. Which means that technically babies conceived this way end up with 3 parents. So, with IVF lots of people who may not have been able to conceive a child on their own, are now parents.

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