‘So, what finally made the difference for you – that you’re really pregnant?’ my friend Sharon asked me. She wasn’t the first. As a columnist who publicly detailed my fertility journey in The New York Times Motherlode blog – covering three years, four miscarriages, and nine rounds of in vitro fertilisation (IVF) – I had just announced I was in my second trimester. It looked like this pregnancy was going to stick. I was 44 and my husband Solomon 48, and we were finally going to have a baby!

But how, asked readers, many of whom were themselves trying to conceive or had a friend or relative doing IVF – the process of stimulating a woman’s hormones to produce extra eggs, then extracting them, fertilising them with a man’s sperm, and transferring the resulting embryos back into her uterus. (IVF and other assisted reproductive technologies account for 1.5 per cent of all American births.)

‘You’re my beacon of hope,’ said Sharon. ‘What made it work?’ I did not want take myself off her pedestal, or steal her faith, but I also had to be honest. ‘I used donor eggs, you know,’ I said.

‘Oh,’ she replied, not bothering to disguise the disappointment in her voice. ‘Donor eggs. OK,’ she said sadly and quickly got off the phone. No congratulations, no happiness, no nothing.

I was carrying our child, made from my husband’s sperm and an egg from a stranger. The child would grow inside me from the time it was an embryo just five days old. With science increasingly showing that unborn babies can feel, perceive and learn in utero, getting pregnant with a donor egg caused me to rethink my ideas about mother-child bonding, the meaning of attachment, and motherhood as a whole. The more this baby grew inside me, the more I felt love for her.

Yet to Sharon and many others I had failed. I’d failed to achieve the holy grail of fertility treatment: having a child with my own and my husband’s DNA.

Among those trying to conceive, there’s a hierarchy of preference for how. Obviously, the easiest and least costly is just plain sex. Then there’s IVF – today, such a ‘normal’ medical procedure that people often don’t mention it. And why should they? These ‘test-tube babies’ use the mother’s oocytes and father’s sperm, so they’re genetically related to both parents, not to mention carried by the mother: equal in almost every way to natural conception.

Lower on the totem pole is what’s called ‘third-party reproduction’, the use of an individual outside the primary relationship to make a baby possible. Everyone knows about sperm donation, with thousands of banks where you can choose a guy like from an online dating profile; single mothers are not ashamed to admit creating a child using their own genes combined with those of a (tall, hot, smart) stranger. It’s so acceptable there’s even been a Vince Vaughn comedy – Delivery Man (2013) – about it.

Surrogacy, in which a woman outside the relationship carries the couple’s embryo until birth, has also made it to the mainstream. There’s the 2008 Tina Fey/Amy Poehler movie Baby Mama, not to mention countless celebrities such as Jimmy Fallon and Sarah Jessica Parker telling the world that surrogates carried their babies, created from the couples’ own sperm and eggs.

Even adoption has changed. Instead of being shrouded in secrecy, with the children themselves often not knowing, the fact is now proudly broadcast to the world, which looks upon it as nearly saintly, parents ‘saving’ unwanted children.

The only thing that still seems to be a secret in these uber-confessional days is women who use donor eggs.

Their numbers are not small. In 2013, out of some 175,000 fertility cycles in America, slightly more than 10 per cent used donor eggs according to the Society of Assisted Reproductive Technology’s (SART) National Clinic Summary Report. And of 63,286 babies born through IVF, 9,512, or 15 per cent, were from donor eggs.

Which makes sense: a woman’s fertility – or lack of it – is often dependent on the age of her eggs, not of her body. The highest cause of infertility is Diminished Ovarian Reserve, which means fewer eggs of worse quality, unlikely to result in a live, healthy baby. Hence the push for women under 35 to freeze their eggs – to stop time just as their fertility begins to decline.

According to the 2013 stats, a woman under 35 – the lowest age range that is counted in the statistics – has a 40.1 per cent chance of having a baby by IVF; however a woman over 42 has only a 4.5 per cent chance. Yet a woman of any childbearing age who uses fresh donor eggs has a 49.6 per cent chance of having a baby.

Of course, the word ‘donor’ is just a euphemism in most places. The eggs are often purchased, except for those from the few family members who actually do donate their eggs. To avoid having the eggs classified as organs, which are illegal to sell, people technically buy the donor’s cycle, regardless of how many eggs result from it.

Around the world, laws regarding egg donation vary: in the United States, egg donation is legal and donors may be anonymous; they can be paid up to $10,000, with travel costs and medical care on top of that. Add another $12,400 on average for IVF, which must still be done, only it is the the donor who is stimulated with hormones and has her eggs extracted. In Canada, the donor egg is legal only if it’s free and the donor known; in France, donation must be free and the egg donor anonymous. French donors are compensated €500-€1,000 in personal profit, with the process itself costing €4,500 more. This contrasts with Austria, Germany, Italy, and Norway, where egg donation is outlawed.

Costs hardly explain why women who use donor eggs keep it such a secret. After all, gestational surrogacy in the US ranges from $100,000 to $150,000, while domestic adoption ranges from $30,000 to $44,000 or more.

‘If IVF didn’t work out, we’d probably just adopt,’ my friend Sharon later told me, echoing what many others have said – inexplicably, since a fertilised donor egg still contains half the parents’ genes and is carried by the mother, while adoption has no biological connection at all.

‘There’s a stigma. Egg donation is looked down upon,’ says Marna Gatlin, founder and CEO of Parents Via Egg Donation (PVED.org), a non-profit organisation founded in 2008 to support, empower and educate egg donor parents. She says people call it ‘weird’ or ‘unnatural’.

‘They don’t tell. They do not tell,’ she said of parents going public about the process. (Telling their own kids is a different story: she herself is a parent to a teenage son who knows his donor egg origin story.) ‘A lot of donor-egg-intended parents are as deeply in the closet as same-sex people were in the 1970s. We’re trying to remove that stigma.’

When we adopt a child, a birth mother selects us, but with an egg donor it’s the other way around

It’s going to be tough. ‘Pregnancy is only nine months but genetics are forever!!’ wrote one person upon learning I had opted for a donor egg.

After learning my donor was anonymous, a person from the adoption community wrote to tell me I’d be ruining my child’s life. It appeared to the writer that not knowing much about the donor was akin to doing a closed adoption and denying the child knowledge of its birth parents.

‘Some people refer to donor eggs as half adoption,’ explains Gatlin, ‘but it’s not accurate.’ For one thing, she says, the mother carries a donor egg child. And for another, when we adopt a child, a birth mother selects us, but with an egg donor it’s the other way around. ‘We select the egg donor,’ she emphasises.

Lori Gottlieb, a Los Angeles-based psychotherapist who specialises in reproductive counselling, thinks the stigma around donor eggs has to do with aging. ‘People associate donor eggs with aging more than a surrogate,’ she says, noting that women of all ages may have to outsource pregnancy due to problems with their bodies. But it’s often older women who need to use donor eggs. ‘It’s incredibly shaming and judgmental: “you waited too long and shame on you and you’re too old,” people think.’ She observes that people seldom say ‘Why don’t you just adopt?’ to a couple who use a surrogate. ‘We value a genetic connection more than an emotional connection.’

Our fertility plan always included donor eggs as the next step if IVF using my own eggs failed. After we had genetically tested our embryos and found them all to be chromosomally abnormal, probably because of my age – 43½ – we had to ‘escalate’, as Solomon liked to say. But as I began floating the donor egg idea around to people, I got some strange reactions.

‘This would be the first time we wouldn’t know who the mother is,’ my father joked in his usual poor taste. ‘I would be the mother,’ I wanted to reply, but bit my tongue.

‘Would the donor be Jewish?’ my brother wondered. True, both the men in my family were Orthodox Jews, obsessed with genealogy and matrilineal descent of the tribe.

But it wasn’t just religious people. I started to notice how obsessed with genetics everyone was – myself included. ‘Oh, is that mommy’s nose?’ I cooed to my younger sister’s new son, assigning his eyes, lips and chin to her or to her husband.

This explains why the general public values a couple using a surrogate (with their genetic embryo) over a woman who uses a donor egg and carries the baby herself. It also explains, for women, the popularity of sperm donation over egg donation. Many women believe that if they’re not using their own eggs, they ‘might as well’ adopt. All seem to discount the effects of carrying the unborn child for 40 weeks.

But they should not. A whole body of evidence now shows that deep bonding between mother and unborn child occurs during the nine months of gestation. And the science of epigenetics – in which environment shapes gene expression – means that nurturing the unborn can influence lifelong temperament and health. Scientists liken epigenetics to a switch that turns gene expression on or off. The overall DNA doesn’t change, but gene influence does.

Some of the impact is blatant. Through such direct actions as poor nutrition and second-hand smoke, maternal environment during gestation can directly influence everything from foetal birth weight to risk of future adult coronary disease. An unborn child bathed in the roiling hormones of maternal stress will have different gene expression – indeed, a different brain – from a child gestated in calm.

But much of the influence is nuanced. ‘There’s a lot of misinformation when it comes to this whole area of prenatal development, even among people who work with babies every day,’ says the psychiatrist Thomas R Verny, author of The Secret Life of the Unborn Child (1981) and widely credited with launching the field of pre- and perinatal psychology. Verny says that ‘bonding and communication happens in third trimester for sure, maybe even earlier’ and cites a wide body of research to make his point.

One classic study was published in Science as long ago as 1980 by the University of North Carolina Greensboro psychologist Anthony Decasper, who showed that newborns were clearly attuned (and attached) to their mothers’ speech from before birth. To conduct his study, Decasper had 16 pregnant women tape-record readings of children’s stories, and read the same story to the child a few times a day. Then, after birth, babies were able to toggle between various stories by sucking on a nipple hooked up to a sound system. Thirteen of the 16 newborns chose the story their own mother had repeatedly read. In a 1994 follow-up study, Decasper found that when newborns were exposed to a rhyme recited by their mothers from the 33rd to the 37th week of gestation, their heart rates slowed – a sign of calm.

By 2007, the neuropsychologist Ruth Feldman of Bar-Ilan University in Israel had shown that the degree of attachment between newborn and mother was influenced by levels of the intimacy hormone, oxytocin, measured in the mother’s blood before and immediately after birth.

And evidence for the connection between an unborn child and a mother only mounts. In a study published in 2015 in PLOS ONE, the psychologist Viola Marx of the University of Dundee in Scotland found that when mothers touched their stomachs, unborn babies reacted with more head, arm and mouth movement; when mothers spoke, those babies reacted with less head and arm movement. And all this responsiveness was recorded not just in the third trimester but also the second, much earlier than previously assumed – though responsiveness increased as gestation advanced.

People are too anxious about the idea of connecting to their unborn child. ‘It’s almost like helicopter parenting in utero.’

‘The mother was once regarded as a vehicle, a conduit for nutrition and waste removal for the foetus that lived isolated from the outside world,’ the study authors wrote. But now we know that newborns ‘preferentially respond to maternal voice hours after birth, suggesting that the foetus is able to detect stimuli in utero and form memories of them’. Parents have long spoken and sung to their unborn child throughout pregnancy, reporting changes in the behaviour of the foetus as a result. Now, with the Dundee findings, it appears that real communication is taking place.

All this adds palpable new context to the existing fertility hierarchy and serves to elevate donor eggs up the ladder of desirability – at least as far as I can see. From this perspective, one could equate surrogacy and adoption as equivalent in terms of prenatal bonding on the one hand while natural conception and donor eggs or sperm are equivalent on the other. ‘So what if the baby’s hair is blond and his eyes are blue,’ says Verny. Even if the child is genetically yours, ‘the personality might be very much influenced by the first nine months.’ The period of gestation could have more influence over the baby’s future than mere genes. Carrying a baby is a bonding tool.

Of course, attachment is a complex business, and can be forged after birth, too. ‘What is important is how you attach to your child when you have a child,’ says Gottlieb, who herself used a sperm donor to conceive. People are far too anxious about the idea of connecting to their unborn child, she feels. ‘It’s almost like helicopter parenting in utero.’ For her, ‘the more relaxed and confident the parent, the better the attachment is going to be’, no matter how the child is conceived or carried.

Let it be said that I am not sure what to believe: whether it’s genes or early childhood or the prenatal environment or a mixture of all three. I myself am the second of four children, and I am absolutely nothing like either of my parents – biological, I must point out – nor like most of my siblings. My younger sister, tall and pretty, with light skin and light hair, doesn’t even look like me, short, dark and exotic. And despite our closeness, our personalities are night and day: me a risk-taking non-planner who lives by the seat of her pants, she one who prefers a more orderly life. My youngest brother, an ultra-Orthodox rabbi (he looks like me beneath his beard) is most similar to me in temperament, humour and even constitution; we hate the same foods and share the same ailments, even though our life choices conflict in every possible way.

Was my mother, prone to depression, in a better state of mind when she was pregnant with me and my brother, six years apart? Or was she just in a better state after we were born? Or were the two of us just genetically better equipped than my two sisters to deal with life’s curve balls? Or is it just a matter of free will: my brother and I persevered better in coping with our parents’ disastrous union (after 29 years of cold war, they divorced when I was 23).

I patted my stomach at a Billy Joel concert, hoping to get some pop music influences in before my husband created another jazz aficionado

All this is to say that since biological parents didn’t work out all that great for me, I’m the last to judge when it comes to fertility choices. Despite sharing my journey oh so publicly, I believe that such decisions are personal, and that any option – including a life that is child-free – can be full of joy.

See, if donor eggs hadn’t worked out for us, Solomon and I would have pursued adoption: we would have done whatever it took to start our family. And I’m sure I’d have felt like Becky Fawcett, the founder and president of Helpusadopt.org, who adopted two children after her fifth round of IVF failed. ‘Once that baby comes out you’re a mom, period. It doesn’t matter how you get there.’

Yet having that donor egg grow inside me was an experience I would not trade. If at first I fretted that I’d feel the baby wasn’t mine, by the middle of my second trimester, with the first faint hiccups of life, then the powerful kicks and flailing of the baby’s arms and legs, I fell in love. I couldn’t help but marvel at my baby’s movement when my husband lovingly caressed my stomach and talked about his day or played jazz on his guitar. I wondered if the baby could hear my thoughts, because I was sure I could. ‘Yes, I know you’re thirsty, I’ll get some water,’ I’d say aloud. Or: ‘This music is too loud for you, I know.’ I patted my stomach at a Billy Joel concert, hoping to get some pop music influences in before my husband created another jazz aficionado, which would leave me the odd one out.

We were bonding, all three of us, for at least half of our nine months together. By then I didn’t wonder how, by the time the baby came, she could feel like anything but ours. And then she arrived, little Lily, at 6 lbs, 10 oz, the squirming gorgeous life form that had been growing inside of me for the last 40 weeks. As they placed her on my bare chest, and her father put his warm hand on her bony back, she settled down, with her – our – family.