In 1951, two babies were accidentally switched at birth. One of their mothers knew the entire time.

Listen to this story being read by Adrienne Tam, here. 

In 1994, two 43-year-old women – Martha Miller and Sue McDonald – received identical letters.

The letter was from Mary Miller, Martha's mum... who was also Sue's mum. Because Martha and Sue were switched at birth.

Mary and Norbert Miller were Martha's parents ...and Sue's biological parents.

Kay and Bob McDonald were Sue's parents ...and Martha's biological parents.

The letter began:

"Dear Martha and Sue, have you ever suspected or been told that we took home the baby that belonged to Kay and Bob McDonald and they later took home the baby that belonged to us?"

Remarkably, both the Millers and the McDonalds were familiar with each other. Their families went to the same church, they had mutual acquaintances, and they lived only a short drive away from one another in Wisconsin, US. 

Even more remarkably, Mary had known about the switch since the time Martha and Sue were babies, and was only now, 43 years later, telling them about it.

How did Martha and Sue get switched at birth?

The story of Martha and Sue was recounted in the podcast This American Life in 2008.

The women were born on the same day in the same hospital in 1951.

However a mistake happened - Martha was given to Mary and Reverend Norbert Miller, and Sue was given to Kay and Bob McDonald.

Mary suspected something was amiss the moment she took Martha home.

"I had complete anesthesia, so was asleep when our baby was born. The nurse weighed the baby and must have left her in the delivery room until after Kay's baby was born very soon after mine," Mary wrote in the letter.

"When we took our baby home, she sneezed five times in a row. I thought that was strange. Never had that happened with any of our others. We had a baby scale at home. When I weighed the baby, she weighed two and 1/2 pounds less than her birth weight."

Listen: Parenting podcast This Glorious Mess. Story continues below.

Mary was sure then that there had been a mix-up. But when she spoke with Norbert about it, he did not take her seriously.

And there was the added complication of their relationship with their doctor, Dr. Deslack. The doctor's wife had been ill, and Norbert, in his capacity as a reverend, had visited her many times. Because of their help with his family, Dr. Deslack refused to charge the Millers for any medical issues – and since they did not have much money, they could not afford (literally) to get on Dr. Deslack's bad side.

Still, Mary would have pursued the issue further but a week after Martha's birth, she was rushed to the hospital after suffering from convulsions. It was so bad she thought she was going to die. The illness lasted for several months and by then, everything was even more complex. How could she take a six-month-old baby away from the only mum she'd ever known?

Did Martha and Sue have any inkling about the switch?

Over the years, there were signs that Martha and Sue were different to the families they grew up with.

"As Martha grew, she did not look nor act like any other children. She was a delight to all of us, so pretty, so photogenic, so full of life. Our other children were very serious. Martha excelled in music, was a great cheerleader at school, very popular, and a blonde. Our other children had dark hair and all needed glasses for nearsightedness. Martha did not need glasses," Mary wrote in the letter.

Mary and Reverend Norbert were parents to seven kids in total. On the other hand, Kay and Bob McDonald had just two kids – Sue and Bob.

Sue noticed that she did not look like her parents or her brother, and she was always more bookish and serious than them.

"In junior high, I remember my friend said to me, you must be adopted, because you do not look at all like your parents. And I said, 'I don't know'," Sue told podcast This American Life. "I asked my mother. I said, 'am I adopted?' And she said, 'oh, no, no'. She says, I was pregnant and you are my child. I wanted a baby, you know, and you're my baby. You were not adopted."

At the same time, Martha – nicknamed Marti – was also noticing how different she was to the Millers. As her mother noted in the letter, she was blonde where everyone else was a brunette, and she was much more perky and extroverted.

"I don't think that they ever came to watch me cheer in a game. That wasn't something that they would have done, because athletics was really not of value to them at all," she told This American Life. "I was just not ever meeting their expectation of intellectualism. And my mother has told me since then, you know, I really didn't expect that much from you, because I knew that you weren't our child. That was a hard thing to hear."

When she was 21, Martha was actually told that she might not be a Miller by her brother-in-law. She asked her mother then about it and Mary gave her a noncommittal answer. The thought that she could have been switched at birth stayed on her mind, and so when she was in her mid-30s, she told a counsellor. The counsellor asked if the McDonalds knew anything about it.

"And I said, 'I don't think they know anything about it'. So she said, well, if you were to find out that these parents that you have are not your parents and the other family doesn't want to have anything to do with you, how are you going to feel? And I said, well, I don't know. I don't have any idea," Martha said.

"And she said, you really need to consider how that's going to change your family for you and how it's going to change relationships for you. So she said, unless there's a real reason that you need to know, she said, I don't recommend that you dig into it."

So Martha left it at that.

Mary tried to "prove" that Sue was her biological daughter in a number of admittedly strange ways over the years. This was due to her personality – Mary saw things as black and white, and could be quite matter-of-fact, as evidenced by the letter she wrote to Martha and Sue.

She invited the McDonalds over to dinner so they could see how much Martha looked like them, and how much Sue looked like the Millers, she would write letters to Kay – Sue's mum – and address Martha and Sue as sisters. She even said, point-blank to Kay's face, "Did you ever think that our girls were switched at birth?"

Kay found it ridiculous at the time. "I said, 'heavens, no'... And of course, I was very busy, because I was chairperson and I had so many other things to do. So I passed it off. But that's all she said. There was nothing any further. It didn't bother me, because I couldn't see any merit to it. I didn't have a doubt in my mind. And I'm not one to borrow trouble."

Mary tried to convince Norbert of the truth to no avail. "I couldn't do anything about it. Norbert and I had a good time while we were together. But Norbert should have gone back and said, this isn't our baby. And this was a bad decision. But he didn't realise what effect that would have on everybody to make a decision like that," she said.

Martha and Sue don't blame Mary for accepting Norbert's denial as gospel. They are not angry with her and understand why she didn't say anything sooner.

Why did Mary finally tell Martha and Sue the truth?

It was only after Norbert laid eyes on Sue at the McDonalds' 50th wedding anniversary party on July 10, 1994 – more than 40 years after the switch – that he could finally accept the fact Sue was his biological daughter.

"When he saw you, Sue, he said, 'I don't need a DNA test. Sue is ours'," Mary wrote. "She looks just like [their other daughter] Mary Lydia. Would make a good twin to her."

After all the years of holding onto the truth, Mary felt immense relief.

"I wanted him to agree with me. And he did. He finally did," she said. "But boy, it was a relief for me. Because that was terrible to have that hanging over you all of the time. It's sad that it happened. It took Kay an awful long time. And I'm sorry for her."

She decided to send the letter about a month after the wedding anniversary.

"So now we are both aware of what happened 43 years ago. We love you, Martha Jane – I'm sorry. We love you, Martha Jane, as dearly as our other six children. I think you know that you will always be our daughter," Mary wrote in the letter.

"But I thought each of you should know your biological and spiritual backgrounds. And know you have mixed feelings about this revelation. I have much anguish and many tears. But I feel I must get this out in the open, so you two know how wonderful that you both are Christians and great workers in the church. Do let me hear from you. I love you both. Thanks, and Jesus lead you in this time.

"Happy 43rd birthday to you, Sue. And to you, Martha. Lovingly, your mum, Mary Kay Miller."

What happened next?

Sue, by then a married mother of three living in Michigan, was understandably stunned. 

She sought blood tests to be absolutely sure, which proved without a shadow of a doubt that she was indeed the daughter of Mary and Norbert Miller.

She didn't tell her parents – the McDonalds – right away because she was worried about her father's health and how he would take the news. She was also worried her mother, Kay, would reject her, especially as she did not like the Millers.

"It was confusing. And then after I knew that I had been switched, and that I had different genes, and my parents kept talking about these people that were so odd, the Millers, because Reverend Miller, he is an evangelical preacher. He wants people to know Jesus Christ and that they would be saved," she told This American Life.

"And I'm really like that too. Sometimes my mom thinks I'm a little fanatical. I'm really a Miller. What does she think of me? I mean, that's my biological family. So I did think, yeah, she's going to know that's not my daughter. And she's going to get this popular Marti, who's so fun-loving and looks like her. And then she's going to say, well, I don't need that daughter anymore. She's part of that odd family."

Sue met with the Millers and got on well with her biological parents and six siblings. She then went for dinner with Kay and Bob, and told them about the letter and blood tests.

"And like my dad said, 'you are my child. I changed your diaper'," Sue said. "And my mother, nothing was going to be different between us. Mrs Miller has, for 43 years, been longing to see the child she'd given birth to. So she's excited about it. And my mother's like, 'what happened to my life?' It exploded."

Sue and her brother Bob had never been close. When Sue told her brother about the switch, he called his biological sister, Martha, immediately.

"When she got on the phone, I was just totally blown away," Bob said. "The way she pronounced her words were identical with the way my mother talked. She could have been my aunt or my mother talking on the phone. And I knew that she had to be my sister.

"And I was super anxious to meet her in person. And until that time, we just talked all the time. With every phone call that we made, we opened up more to each other. And we had the same personality. And we think so much alike."

Siblings Martha and Bob got on so well that, as the years went by, Sue would get anxious if Martha was at a family gathering. She would sometimes feel neglected by Bob and break down and cry.

Watch: Arlena and Kim were switched at birth. Story continues below.

Martha, who like Sue was also married with three kids when she received the letter, also had a tough time finding out the truth. Some would say it was harder for her than for Sue.

"There were a few years there, where every chance my mother got, she made it perfectly clear that I was a McDonald. For the longest time, whenever she would write to me, she would include McDonald in my name. Just absolutely bizarre things like that. That's just how she is. There is no grey area," Martha said to This American Life.

"Actually, my mother wanted to go to court and have my name legally changed back to Sue McDonald and have Sue's name changed. That was her idea. She tells me that you're my daughter. But at the same time, when she refers to Kay, she says, well, 'your mother is doing such-and-such' or 'your mother said this'. And when I think of my mother, I think of her."

Martha and her father, Reverend Norbert, began talking on the phone a lot and he let her know he still loved her. Their relationship strengthened.

"My dad had this horrendous guilt because he felt like it was all his fault that he should have believed my mother for all those years. And I think he honestly never thought it was a possibility. He thought she really dreamed this up in her head and just got obsessed with it," she said.

"And the other thing was that he really thought, what difference does it make? A child is a child. She's with us. She's ours now."

The McDonalds kept Martha at arm's length because they wanted to protect Sue, and were confused in their own right. The rejection stung, and Martha felt the counsellor's words from all those years ago were indeed coming true.

"I want you to know that I will accept whatever contact you choose to have with me, even if it's none at all," Martha wrote in a letter to the McDonalds. "I promise you, I'll never try to make you think of me as your daughter. I know that Sue's your daughter and no one could ever expect you to feel otherwise."

So while the Millers and the McDonalds embraced Sue with open arms, the McDonalds did not do the same for Martha.

"[Sue] had both families wanting to make sure that she was included in their family. The Millers wanted to incorporate her family into our family as quickly as they could. I did feel in the beginning like she was taking my place in my family. And that was odd, very odd," Martha told This American Life.

"And sometimes I don't know exactly what her relationship is with my sisters. I honestly don't know how much they communicate, how much they're in touch. Part of me really doesn't want to know, because I think I would feel left out of something."

At that time, Kay was understandably angry and upset with Mary for not "correcting things" back in 1951.

"Well, of course, [the Millers] were really clamouring to get to know [Sue]. And I felt excluded. I felt they were trying to take her away from us," Kay said. "And Susan always had said to me, Mum, why didn't you have any more children after I was born? She wanted to be a part of a big family. So then she found out she has all of these brothers and sisters. And the phone calls were fewer.

"And of course, Marti didn't really call a whole lot. She's a very busy gal, and I was not having that much communication with her. And I thought I was losing both of them."

It took eight years for Kay to really sort through her feelings. While she is no longer angry in the way she was, she still doesn't understand why Mary kept silent.

"If I had as strong a feeling as she did that I had the wrong baby, I would have pursued it. I don't care whether my husband objected or not. I feel like I should have made a wrong into a right," she told This American Life.

"I only had one daughter, and she had five daughters. In fact, we weren't even sure we'd have another child. So of course, we were elated when I did get pregnant. And then to think that I didn't get to raise the one that I had wanted so much. So I never will probably understand why. I've forgiven them, but that doesn't mean that I've forgotten. I can still wonder why and probably never will know why it didn't come up any sooner."

Neither Martha nor Sue really let themselves think about the 'what ifs'.

"I really only thought about that one time. I only let myself think about it one time. It was actually right after I met them. And I was going back to my mother's house and I was driving. And it was then that I started thinking, oh, my gosh, my life would have been so different," Martha said.

"And the more I thought about it, the more I realized, you know, I can't think about this, because it'll drive me crazy if I do. And so I kind of made a promise to myself that I would just never go down that road again, that I was just not going to go there. And I really haven't, because there's no point."

As the years have progressed, the relationships between both families and Martha and Sue have grown and evolved. Kay and Martha are much closer than they used to be.

At a family gathering, Martha and Sue spoke about their childhood bedrooms. Martha had shared a bed with her sister, Faith, because she had six siblings.

"You had your own room, didn't you, all to yourself?" Martha asked Sue.

"I had my own room. Yes, I did. And my own bed, too, everything," Sue said.

"That's what I'm talking about," Martha said. "Yeah, whatever. It was a different life."

Feature image: Getty.

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