It’s 1.24pm on a Friday afternoon and Trish Moodley is trying to make a baby, while I watch. The scene is not completely unromantic: the lights in the room are dim, out of a radio on a high shelf Madonna sings Get into the Groove, and I shuffle close to Moodley, an embryologist, as she sits at a microscope. With a squeeze of a trigger, Moodley shoots a sperm into an egg. This is what few ever get to see: human life in its first seconds. Even the parents are miles away, anxiously waiting by the phone. I am awestruck.

“If you stop to think about it,” says Moodley, “it’s quite scary, but you get used to it.” She has six more potential people to create before lunch.

Welcome to the strange world of embryology: the hidden science behind the IVF industry, whose booming popularity is twinned with controversy. On Thursday a fundamental change in the law on storing and experimenting on embryos comes into effect, needed because of the pace of change in people having babies the new-fashioned way. About 35,000 women a year undergo IVF in Britain, rising by 6 per cent year on year. To mark this, I was given rare access to the embryology laboratory at the Barts and The London Fertility Centre.

It is one of the strangest workplaces I have seen, combining the high science of a space mission with the emotions of a Daily Mail front page. As the mystery of nature is stripped away, so come different mysteries. Why do some women get less NHS treatment, essentially less chance of parenthood, depending on where they live? Why do IVF clinics perform so differently, if they are all doing the same procedures? How do you stop a mix-up of someone’s embryos? And do you ever wonder how an unwanted embryo is destroyed?

One woman having her embryo put back today says the embryologists “have the best job in the world”. She envies their amazing feats in the lab, their optimism, while, all around her, fellow patients are so desperate. “It’s bizarre, none of the patients talk to each other, some of them look really sad.”

Not that she gets to see the embryologists’ work. Patients are barred, but few doctors enter their domain either. While doctors treat the patients, often becoming medical superstars, embryologists create and care for the embryos. Here, in the NHS, the embryologists’ pay is a fraction of the doctor’s, £29,000 to £45,000. In private practice the best embryologists are hot property, poached for many times that.

On the left of the lab is an open doorway to an operating theatre, where a pair of bare legs can be seen, belonging to a patient having her eggs collected. On the right side of the room is an open doorway where another woman’s legs can be seen. She is having her embryos, created a few days ago, transferred back into her body. In between is the lab, lights are lowered so as not to activate the embryos, but this only emphasises the air of the sacrosanct.

“We get such a thrill from the pregnancies,” says Moodley, and then her smile falls. “But very rarely do people come back to show us their babies. I think they don’t want to remember the horrible times they went through before they had a child.”

Here Moodley, and her colleague Konstantina Anagnostara, man the microscopes. Anagnostara is on egg collection rota, which means she must rush, with a test tube, from the doctor in the operating theatre, back into the lab, examine the egg under a microscope, and transfer it to an incubator in just a few minutes.

I catch her mid-way through as she, at her microscope, spots a hazy pale blob under the microscope: “One egg, that’s seven so far!” she shouts to the medical team around the woman, before transferring the egg into a plastic dish and speed-walking back for more, a good haul of 12 in total.

It has the rush of a Gordon Ramsay kitchen — yet one false move and something utterly precious could be spilt on the floor. Or, perhaps worse, wrongly assigned. Only last week, a woman in America was informed that she was pregnant with the embryo of another couple, similar cases make headlines every year.

This is why, every time a sample, be it sperm, eggs or embryos, is transferred to a different place, such as a new test tube, two embryologists must “witness” it. This happens all day, staff reading out names to each other, double, triple checking. Still, they know they are vulnerable to human error. If even a small mistake is made, “it’s heartbreaking”.

“Everyone makes mistakes,” says Anagnostara. “And if you haven’t, you haven’t worked in embryology long enough. You tell senior staff straight away, and it gets reported. But this is not a job where you can go out drinking the night before, or go into automatic mode. I love it because it is about making a difference in people’s lives, but equally you can mess things up, it is a big responsibility. Everyone has questioned whether it is worth that pressure.”

The next step of the process is fertilisation. Here the embryologists in the team, mostly in their late twenties, nearly all female, bend over microscopes to tend to the eggs of women, mostly in their late thirties. They are young because embryology is such a new science — but no one can explain why embryology is so female dominated.

Moodley examines the egg of an older woman; it is grainy, shrinking away from its edges. “Not the best egg I’ve seen.”

They are non-judgmental about the increasing age of their clients. Does Anagnostara think some couples go to extremes to achieve their dream of becoming parents? “No,” she says. “I would find it extreme if they didn’t want to do IVF.”

About half of the IVF treatments now involve intra-cytoplasmic sperm injection (ICSI). It is both the favourite and most nerve-wracking part of the embryologist’s job. In traditional IVF, the sperm and the egg are left alone in the privacy of a small pot. In ICSI the embryologist chooses the best sperm for injection, after banging its tail.

Banging its tail? I watch Moodley sit down at the “ICSI rig”, a massively high- powered microscope, where she, within seconds, selects the strongest sperm and, before injecting it into the egg, slaps its tail with the needle. It is stunned.

“Otherwise it would get too excited, and swim around inside the egg, destroying it,” she explains.

Then the egg goes back into one of the incubators that line the walls, looking like kitchen fridges, except they are stacked with pots of embryos nicely cooking at body temperature. The next morning Moodley will call the patient, who is waiting by the phone, “usually terrified”, to hear how many of her eggs have fertilised.

This clinic’s success rate is above the national average, but rates vary wildly between centres. Part of the issue is how long an embryo is grown before being transferred back — five days is ideal but until recently many clinics were waiting for just two days. The clinic at Barts has been growing five-day-old embryos for a year, although leading private practices made the switch several years ago. For maximum effectiveness, the clinics also need to be able to transfer embryos seven days a week — something this clinic is just about to do, and others are still to follow suit.

Anagnostara is now working the left side of the room, choosing which of two embryos to return to a woman. She sucks one into a syringe and carries it to the doctor. In that split second a fate is decided. Do embryologists feel they are “playing God”? She tells me off for sentimentality.

“You have to think like a scientist, you cannot imagine whether one is going to be a musician or whatever. It is up to the embryo what it wants to become. All I want to do is help the couple get pregnant.”

The chances aren’t great though, I say (babies will result from, at best, a quarter of IVF cycles).

“It’s better than nature.”

Suddenly, there is a snag. This patient wants to freeze her unused good embryo, but her primary care trust does not pay for frozen embryo transfers. The doctor has to go through the rules with her. The next patient comes from a different part of the country and so is under different rules. The embryologists find the postcode lottery so complicated that they have to keep referring to a large file to advise each NHS patient on their different rights.

The unused embryo of the patient with the wrong postcode will not end up in one of the centre’s large freezers, where they used to be destroyed after five years. The new law will extend this to up to 55 years, to cover patients who, because of disease such as cancer, may need to freeze eggs or sperm in childhood.

What happens to a discarded embryo? The embryologists point me towards a prosaic bin in the corner of the lab, where discarded embryos are put after many rounds of procedural checks. Sure enough, when I look in it, along with some latex gloves, is a discarded glass dish, contents spilt. The embryos, a few days old, won’t survive very long out of the incubator. As is standard in IVF clinics, the bag will later be incinerated along with other clinical waste.

Two weeks from now, the women from this morning’s transfers will take pregnancy tests. Life goes on.

IVF in numbers

55 years is the new time limit on the storage of embryos

3.5 million people in the UK are believed to be affected by infertility

34,855 women had IVF treatment in 2006

10,242 women gave birth to

12,596 babies in 2006 as a result of IVF

£5,000 is the typical cost of a cycle of IVF