Assisted Reproduction 101

I started what I think should be the last phase of the baby project. I don’t know yet if his sample can be refrozen. So for all that it’s worth – this may be my last shot at it. Hoping to get a lot of good embryos. But while I go through this, a lot of people have been asking me questions on what’s it all about. How it works etc. etc. and in some cases the questions really surprise me. We did this as a part of mandatory curriculum in 10th std – reproductive system. Was no one paying attention?

Anyway, so I though I’ll take some time out educating. Let’s talk about how we make babies.


  1. 1 Egg
  2. 1 Sperm

Note: These ingredients are usually enough in the specified quantities, but in some cases quantity may vary – i.e. multiple births or IVF – but that’s advanced course and we’ll get to that later.

It amazing how many people find the concept of a human egg funny. Where do you think you came from? So let’s just explain the ingredients a bit more and how they are important for making a baby.

The Egg

The woman produces the egg (duh!). A mature egg is a single cell with only one set of chromosomes. Human cells have 46 chromosomes so the mature egg (Oocyte) has only 23.

A woman is born with all the eggs she’ll have for her lifetime. But they are not in a mature state. When the woman reaches puberty, her eggs start to mature – 1 or 2 at a time in her ovaries (see image 1 below for reference). Eggs mature inside structures called follicles and once mature the follicle breaks to release the egg in the fallopian tube – this is what connects ovary to uterus.

Got it? Ovary is where eggs grow. Uterus is where baby grows. OK till now?

Image 1: Image Source

The Sperm

This one isn’t that interesting a story. Sperms are generated regularly by the man and on ejaculation are supposed to swim up to the fallopian tubes to fertilize a mature egg present there. Like eggs, human sperms also have half the chromosomes – 23.

Note: Embryos are made in Fallopian Tube near the ovary.

Making the baby

When the sperm gets to the fallopian tube (keep referring to Image 1) and a mature egg is present there, the sperm tries to break the egg covering and enter the egg. If it’s successful, you have what we call a Zygote or an Embryo. Basically the baby is in progress. This now has a set of 46 chromosomes – one set from each parent. And it now starts dividing into multiple cells. So after 36 hours you have 2 cells when there were 1 initially. After 48 hours you have 4 cells and so on.

But before the baby can start well on it’s way, it has to travel to the uterus and attach itself to the mother. This is where it’ll get it’s food. The attachment later grows in to the umbilical cord. A lot can happen in this journey.

The thing is – not all Zygotes/ Embryos make good babies. Did you as why? Well something could be wrong with the ingredients that can mess up the whole recipe. There could be chromosomal abnormalities that lead to birth defects etc. The egg may not be strong enough, or may not have enough energy to continue helping the baby grow. And so, when biology determines that the baby recipe isn’t going the way it was planned, it stops cooking. The embryo/ zygote fails to implant, and dies off. And no one ever gets to know.

However, if everything is going fine, the Embryo travels up the fallopian tube to the uterus. In 5-6 days it has reached a stage called blastocyst. Till now the membrane of the egg is intact. Now it’s about to break. And when it breaks, it’s time for the embryo to attach itself to the uterus.

When the embryo attaches to the uterine wall, the body gets hormonal signals that the woman is pregnant. These hormones are detectable with pregnancy tests 1 month after the embryo implant or in 2 weeks with a blood test for BHCG.

When in one cycle ~28 days in humans, there is no embryo implant, the uterus sheds it’s inner lining and that’s when women get their period. In a new cycle, the next set of eggs start maturing.

How assisted reproduction works

So till now we figured out the normal process of baby making. Now comes the science. There can be many reasons a woman can’t get pregnant and quite a few of them have to do with sperms. If the sperm can’t swim as far as the egg, there is no possibility of fertilization. Similarly, sperm may not be able to get inside the egg. Or the egg quality may be poor to sustain an embryo. Or the uterine wall may be too thin for the embryo to implant itself. Anyway, whatever the case, in case the couple has an infertility issue they resort to IUI, IVF or ICSI treatments. They all address a specific problem.

IUI – Intra Uterine Insemination.

If the sperm can’t travel far or fast enough, people undergo an IUI treatment. Basically, the doctors would take the sperm, filter it to condense the most agile and strong cells. Heat it a bit to improve speed, and inject this inside the woman through the vagina while she is ovulating – i.e. making eggs.The idea is to stimulate the sperms and give them a better chance to reach the fallopian tubes. The woman is also stimulated to release more eggs than normal to give sperms a better chance at penetrating an egg. In this case, the embryo is formed inside the body and the normal growth an implantation process happens.

IVF – In Vitro Fertilization

The name says it all, but anyways, I shall explain. If there are issues with the woman too, then IVF is a better option. Here the woman is given hormonal stimulants to increase the number of eggs produced in one ovarian cycle. When the eggs mature, a hormone (called luteinizing hormone) is given to loosen the eggs inside the follicles. Then a surgical trans-vaginal procedure is done to pick out the eggs. Basically they stick a needle inside you down there and suck the eggs out. This is guided by ultrasound. Now the eggs are outside your body.

Next the man gives the sperm. So sperm is outside the body too. Then they take a petri-dish and mix up the two. So fertilization is happening outside the body. Not in the fallopian tube, but in a petri-dish. Therefore, these were also called test tube babies. Some sperms fertilize some eggs and a number of embryos are formed. It could be 4,6,15 – depending on the number of eggs retrieved and successfully fertilized.

These embryos are allowed to grow in the petri-dish/incubator. They are still outside the body and stay that way for 3-5 days. Most doctors prefer the 5 day blastocyst stage for transfer. So let’s talk about that. After 5 days, when the embryo is a blastocyst it’s taken from the incubator and placed inside the woman’s uterus. Now the blastocyst (or how I see it as a 5 day baby) is inside the uterus and must attach itself to the uterus wall to continue growing in to a baby. If the blastocyst fails to attach itself, it dies, and the woman gets her period in a few days. If the attachment happens, the hormone HCG is released and can be detected in 2 weeks as a successful pregnancy.

ICSI – Intra Cytoplasmic Sperm Injection

If the sperm quality is poor or if the sperm is unable to penetrate the egg even with IVF, ICSI is recommended. In this the process is same as IVF, just that instead of mixing everything in a petri-dish, one sperm is taken and specifically injected in to one egg to make the embryo. Rest is the same.

Phew! Hope we all are up to date on human reproduction now!

Note: This is by no means an exhaustive account. There are lots of factors at play. Many challenges. This is just an overview. Not to be taken as any sort of counseling.


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