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Identical Vs Fraternal Twins

05 Friday Jan 2018

Posted by frannyritchie in babies, pregnancy

≈ 1 Comment

Tags

di-di, fraternal twins, high risk pregnancy, identical twins, mono-di, multiples, pregnancy, turners syndrome, twins

The thing that struck me about having twins – particularly high-risk twins, since that comes with so many more scans and doctors appointments – is that the whole thing is very, well, mammalian. There are different types of twins, characterised by different placentas and amniotic sacs, and there is a surprising amount of confusion among the non-twin-bearing public about how they work.

So I’ve written a quick guide, and include the usual disclaimer about how I’m not a medical professional, just someone who is surprised by the degree to which people are confused about the biology of twins who’s done a lot of googling.

First, there are fraternal twins. Fraternal twins occur once in about every 80 pregnancies, although the number is going up as maternal age rises and fertility treatments increase the incidence of multiples. Vanishing twin syndrome, in which one pregnancy isn’t viable and just sort of…fizzles….only happens with fraternals.

In fraternal pregnancies, there are two separate placentas with two separate amniotic sacs. They are concurrent pregnancies, but there are no links between the babies in utero; they just happen to be two babies born on the same day. Fraternal twins can be girl-girl, boy-girl or boy-boy, and while many pairs of siblings may look alike, they are no more genetically similar than any other pairs of siblings. There is a genetic component, however: a woman’s likelihood of becoming pregnant with fraternal twins is passed down the maternal line (i.e. mother to daughter), because it relies on a woman’s likelihood of releasing two eggs in any given cycle (though, as mentioned above, there are a number of other relevant factors as well).

The natural world is full of fraternal twins. Every animal that has a litter is, in essence, having fraternal twins.

Identical twins occur once in about every 400 pregnancies, but are (I suspect) less prevalent in the general population because there are some common complications that make fewer identical-twin pregnancies viable. Within the umbrella of ‘identical twin’ there are three separate types of pregnancies:

  1. Dichorionic-dizygotic: two placentas, two amniotic sacs. On an ultrasound, this pregnancy will look exactly like a fraternal pregnancy; in fact, some people do not know until they have genetic testing whether they have identical or fraternal twins even after birth (not all identical twins look alike. Mine don’t!)
  2. Monochorionic,-dizygotic: one placenta, two amniotic sacs. The placenta is divided into two sections, serving each twin individually, but the line can only be distinguished post-partum. This is the most common type of twin pregnancy and occurs in roughly 92% of identical twin pregnancies (though I have also seen reputable websites that claim its more like 60%. Since not all di-di twins will be confirmed as identical there is probably some wiggle room here).
    There are also blood vessels connecting the twins across the sacs; despite the roughly hojillion ultrasounds we had, I was never 100% clear on how that works. In twin-to-twin transfusion syndrome (TTTS), one of the more common and serious complications, the babies’ blood vessels are connected, and one twin receives more blood than the other (donor) twin. Selective intrauterine growth restriction, which is what my girls had, is a similar condition in which one twin has a larger allotment of placenta than the other. Most identical twins are different sizes at birth; sIUGR is diagnosed when one of the fetuses is below a certain percentile (I believe its 10th percentile but I couldn’t confirm that with a quick Google so I’m just going to go with it)
    TTTS affects about 15% of identical twin pregnancies and sIUGR about 10%. If you’re really unlucky, you can have both simultaneously; one does not preclude the other, though the differences between the two disorders are only subtle. Both are not possible in pregnancies without a shared placenta, so do not affect fraternal or di-di pregnancies.
  3. Monochorionic-monozygotic: there is a single placenta and a single sac. This occurs in about 2% of twin pregnancies and is super high-risk. Best practice as of 2017 calls for women with mo-mo pregnancies to be put on bed rest at 25 weeks and deliver at 32. The reason is that there is a risk of the umbilical blood vessels getting tangled within the single sac, which can have really awful, tragic outcomes. Mo-mo pregnancies are also at an even higher risk for TTTS and sIUGR, although I’m not sure why.

The type of twin pregnancy is determined by when the egg splits: if it happens early, you get a di-di pregnancy; if it happens late, mo-mo. Everything in between is mono-di. What surprised me is the definition of ‘early’ vs ‘late’: any egg that splits more than 13 days after conception will result in conjoined twins. Eight-13 days = mono-mono and a split between five and eight days results in mono-di.

One note about identicals: in very rare cases, they can be different sexes if one of the babies has Turner Syndrome and the other does not. Turner Syndrome occurs in 1 in every 2,500 births, but its incidence in twins is extremely small – like, five documented cases ever. Still, I was floored to find out there is any instance in which identical twins can have different sexes.

You may think you don’t know enough identical twins for the 1/400 number to sound right; this is because (I think) there have been dramatic advances in maternal/fetal care for twins in the last decade or so, as well as major improvements in neonatology, which is a fast-moving field. In most cases, the treatment for complications is premature delivery, which on average has much better outcomes now than it did thirty years ago (which is not to say there aren’t lots of healthy humans who were born prematurely out in the world, though there is not great data about how they fare in old age).

When we told my parents we were having identical twins, they said ‘but how do you know?’ and the answer is, there was only one placenta, so it was definitely identical. There is no way to increase your chance of having identicals; it just happens sometimes.

 

 

 

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Christmas frickin’ Magic

29 Friday Dec 2017

Posted by frannyritchie in babies, Parenthood, pregnancy, Uncategorized

≈ 2 Comments

Tags

Christmas, christmas brunch, Christmas magic, Family, holidays, hospital, miscarriage, multiples, placenta previa, preemies, pregnancy, pregnancy complications, twins

The last two Christmases have not been fantastic.

Last year, I finished work on Friday, 23 December, and sat at the kitchen table ready for the holidays. I remember saying ‘I am so excited!’ about an hour before I went to the bathroom and saw blood in my underwear.

For most women, that’s called a menstrual cycle. But I was 23 weeks, 6 days pregnant. I had had an ultrasound earlier that day and it had been positive – it was a high-risk pregnancy but things were generally stable and I left feeling lighter than I had in the past. I was on the cusp of viability! This was HAPPENING!

I was at the hospital less than half an hour later.

The same doctor who had scanned me earlier that day came in, and confirmed that I’d had a bleed but that both girls were still moving. It looked like it might just be a one-off, and then it happened again. And again. And faster and faster.

I chugged water from paper cups in the triage area, running laps between the bathroom and our curtained-off area. A couple hours later, I was transferred to Labour & Delivery – not a positive sign – where I thankfully had a private room with ensuite bath (not all rooms do) and could schlep between the bed and the toilet. I noticed a tiny new stretch mark, running north from my bellybutton, and stared at the blue screensaver on the computer kiosk in a corner of the room, only realising the next morning that I could have turned off the monitor. But by midnight, the bleeding had just…trailed off. The same doctor – bless you, Catherine Aiken – came in to discuss delivery and steroid shots (I got one) and the NICU team came to prep me for the worst. Daphne was 400 grams at that point, and would not have been expected to survive; Fiona, at about 540, stood a fighting chance. Ian went home at about one in the morning and I spent the rest of the night the same way – staring numbly into space, trying to sleep, punctuated with trips to the toilet that confirmed I was mostly not bleeding anymore.

The next morning, a midwife’s assistant brought me tea and toast. I sat on the inclined bed with a Styrofoam cup of tea in my lap and sobbed and sobbed, while my daughters – now an even 24 weeks, and officially Viable as far as the medical establishment was concerned – wiggled and thumped inside me.

I was retrospectively diagnosed with a partial placenta previa, a complication that can be fatal to mum and baby – or can be so minor as to barely register as a complication at all. I left the hospital on Boxing Day, and we had family Christmas two days late. A week later, I had another bleed – a much more minor one – and spent New Year’s in the hospital. And that was last year’s holiday season. Yippee!

That would be enough to feel like I had to bring the Christmas Magic this year, but it turns out there is a theme. Two years ago, I had a miscarriage at 11 weeks pregnant (later diagnosed as having been caused by Graves’ Disease – basically an overactive thyroid), on the 17th of December. It had been an easy, breezy pregnancy to that point – things had gone 100% according to plan with minimal morning sickness, and once we crossed the 9 week mark I thought, ‘well this is fantastic; my chances of miscarriage now are like 2%’

Well, someone has to be in that 2%.

My memories of the miscarriage mostly involve crying: at the ultrasound, when they confirmed there was no heartbeat; in the shower, on the toilet, in my mother’s arms when I found the ‘big brother’ shirt I’d ordered to my parents’ house. Eventually I found a grief anthem: I would sing a chorus from a Ben Folds song and allow myself to feel All the Feels – sometimes I sang it twice – and then I’d pull myself together. All the same, it was a rough few weeks that stretched into months, when we learned that I had to wait until my thyroid was managed to try again.

This year – and every year from now on – I am free from reproductive stress. Our family is complete; this uterus has closed up shop. But as the 23rd of December approached, and I realised that last year would cast a longer shadow than I had anticipated, I felt a lot of self-inflicted pressure to make this holiday special. To start new traditions that would drown out the stress and disappointment of previous Decembers. To celebrate that we had come out of a difficult couple of years with three healthy children. Basically, to create Christmas memories that would drown out the crumminess of the last two years.

Here is the problem: my baby daughters don’t care; my husband doesn’t care (at least not nearly as much as I do); and my son just wants to eat treats and open presents, and will have only the haziest memories of this year if he has any at all. All five of us have colds, except for Theo, who is stuck at home because nursery is closed for the week and is going stir crazy. Holiday perfection has taken a backseat to sleeping and trying not to succumb to our desire to just plop our three year old in front of Paw Patrol and call it a damn day.

Where there has been magic, it has been incidental, which I guess is a good lesson to take from the festive season. Daphne waved at her grandparents and aunts during a Skype call on Christmas, a development that is way ahead of schedule and for which there were many witnesses. In the last four days, Fiona has become an indisputably mobile baby. She doesn’t go fast or far, but she doesn’t stay where you put her, either. Theo’s math skills have taken a step forward – when counting pound coins he received with a piggybank, he got to 8 and said ‘I think I have ten!’ And all three children started playing together for the first time when their new toy, Wobble Bear, was placed between the three of them, which felt like a freaking Christmas Miracle. Some of this stuff was facilitated by Christmas, but its mostly every day stuff that we noticed because we’re all sitting around driving each other a little nuts.

It will take more than one week of bad weather and sick children to erase the scary sadness of the last two Christmases, and an insistence on a CHRISTMAS FAMILY BRUNCH, DAMMIT are probably not going to help. But that’s a lesson in and of itself, and I will take it.

The Tiny Baby Blues

26 Tuesday Dec 2017

Posted by frannyritchie in babies, Delivery, Early Days, Parenthood, pregnancy, Uncategorized

≈ Leave a comment

Tags

complicated pregnancy, early days of parenthood, Family, iugr, multiples, NCT, NICU, NICU aftermath, Parenthood, premmies, sIUGR, twins

I met a family last week who had an extremely premature baby. I had two extremely premature babies, but this baby was so premature that I was reduced to saying, essentially, ‘oh, shit, that’s an early baby.’

I have been thinking about that family a lot since. They arrived at the NICU – our NICU – a couple months after we left and stayed for a long time, though they are home now. But I keep feeling regret for them – not that they spent four months with a baby in the hospital, though that sure sucks a lot – but that they left the hospital without the resources that they would have had if things had gone more smoothly. Its hard to make friends with other parents when your experience diverged so sharply from everyone else’s so early, and its hard to settle into a rhythm as a new parent when you feel alienated from everyone else and their robust, healthy, oxygen-free newborns.

When I was pregnant with my first child, my husband and I did a birth-prep class. We had been warned that the content was not especially useful (it wasn’t), but that there was a lot of value in meeting your classmates – classes are organised by neighbourhood, and we live in an extremely fertile area, so our classmates lived around the corner, down the road, up the street – we were extremely geographically concentrated. When one of the babies was born early, the father sent an email to all of us saying how nice it was to meet everyone and he hoped to see us again soon sometime.

We had a good laugh about that at our fourth annual birth-prep group holiday in October. We saw each other almost every day all summer, and are still in regular contact with virtually everyone in the group, which has swelled (with second and, in our case, third children) to 32 people.

My group are outliers; most people don’t end up taking regular vacations with their parenting classmates. But most people do leave the hospital with a roughly shared experience of birth and new parenthood. Plus a baby. Most people leave the hospital and take their child with them.

For NICU families, it isn’t like that. I found it relatively easy to leave my daughters behind, not because I’m a callous witch, but because they were clearly…not finished. They were in incubators and they clearly needed to be. I found it harder at the end, when we were in sight of a finish line that never seemed to get any closer, and the girls looked and acted like babies instead of fetuses.

Still, from the moment they were born, I thought they were perfect. I wanted to tell people about my gorgeous twin daughters as much as any other new parent. When I was two weeks postpartum, I took my son to a birthday party and people asked how I was. It was only as I watched their eyes widen that I realised I had to adjust my rhetoric a little. ‘I just gave birth to tiny, perfect, extremely premature babies!’ isn’t exactly cocktail fodder. No one knew what to say. I skipped the next preschool party.

Of course there are families in the NICU who are going through something similar to what you’re experiencing. When people ask if I made friends in the NICU, I say ‘well – Facebook friends.’ I did meet people whose acquaintance I value, but none of them live within a twenty mile radius. Catchment areas for Category III (most intensive) NICUs can be huge; there are only a few in the UK. There are always families coming and going, and there is a hierarchy. One woman took weeks to warm up to me, presumably because her kid was having a rough go and she didn’t want to deal with another baby having an easier time than hers.

So I’ve been thinking a lot about this family I met recently, who had four crummy months in the hospital only to find themselves starting from a different place than everyone else who has a baby the same age (actual or adjusted) after they got discharged. I’ve wondered what could be done to make it easier for them, and I’ve wondered what I could do without coming across as an overzealous weirdo. I haven’t come up with much so far.

 

 

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